Tuna

An Important Message About Tuna

We have placed tuna on our "10 Most Controversial WHFoods List." This list was created to let you know that even though some foods (like tuna) can make an outstanding contribution to your meal plan, they are definitely not for everyone. One of the most controversial aspects of tuna is its potential for contamination with mercury. In some areas of the U.S., up to 50% of tuna sold in markets may exceed the U.S. Environmental Protection Agency (EPA) 500 ppb safety level for human consumption. In addition to its potential for contamination with mercury, levels of preformed histamine in tuna make this fish more commonly associated with adverse reactions than other foods. Some species of tuna are also considered endangered. All of these issues contribute to the controversial nature of this WHFood. You can find more information about these issues by reading over our complete food profile for tuna.

Based on all of the research that we have reviewed, we do not think it makes sense for you to rely on tuna as a primary seafood source for key nutrients, including omega-3 fats, since all tuna species show some level of mercury contamination in research studies. However, we do think it makes sense for you to treat tuna as a fish that can be enjoyed multiple times per month, especially if you select tuna types with lower mercury risk. As a general rule, we would include both skipjack and tongol tuna in this lower mercury risk category, and in some cases yellowfin, although this species can have widely ranging mercury level due to its widely ranging size and lifestyle. For more details about our 10 Most Controversial WHFoods, click here.

What's New and Beneficial About Tuna

Researchers have recently discovered that tuna contains the mineral selenium in an unusual form called selenoneine. This form of selenium plays an important role in the health of the fish by serving as an antioxidant and protecting the fish's red blood cells from free radical damage. Interestingly, it is also able to bind together with mercury compounds in the fish's body (including methyl mercury, or MeHg) and lower their risk of mercury-related problems. Because there are approximately 2-3 milligrams of selenoneine in a 4-ounce serving of tuna, we are likely to get some of this same antioxidant protection when we eat tuna. Equally interesting, perhaps tuna will turn out to be a fish that - even when contaminated with mercury - might pose less of a mercury risk than might otherwise be expected due to the presence of selenoneine. Further research is needed to determine if this decreased risk actually takes place, but we greatly look forward to the results of future studies in this area.
In a much-discussed recent study about fish intake and cardiovascular disease, researchers have uncovered a very interesting trend involving tuna. Over 15,000 U.S. men and women participated in this 15+ year study, and their intake of fish - including canned tuna, darker oily fish like salmon and mackerel, lighter non-oily fish like cod, and shellfish like shrimp and lobster - was compared with their likelihood of experiencing a specific type of cardiovascular problem called atrial fibrillation (AF). In AF, electrical impulses within the heart become irregular. In the broadest dietary context, total consumption of fish did not help these participants lower their risk of AF—even if fish were eaten more than twice per week. However, researchers did find risk of AF to be reduced when a specific combination of fish—namely, canned tuna and oily fish like salmon—was eaten more than twice per week. Interestingly, this specific fish combination was more closely related to decreased risk of AF than the total amount of omega-3 fatty acids provided by the fish. While we cannot be sure about the reasons for benefits from this specific combination of fish, the contribution of tuna to decreased risk of this cardiovascular-related problem seems important and worth careful future investigation.
During the preparation of tuna for canning, whole fish are often steamed for a period of hours, and during this process, a watery liquid (called cooking juice) is created that frequently gets discarded as waste by tuna manufacturers. In recent studies, however, scientists have examined the nutrient composition of this cooking juice and determined that small protein fragments—called peptides—are present in the cooking juice and that they possess strong antioxidant properties. The antioxidant properties of these tuna peptides include the ability to protect cell membranes from oxygen-related damage (a process called lipid peroxidation). While the manufacturing of canned tuna is obviously a very different and much more lengthy process than the very short duration cooking methods that you would be using to steam, sear, or broil tuna in your own kitchen, it is still very likely that your at-home cooking methods for preparing fresh tuna will result in creation of some of these same beneficial antioxidant peptides.

Tuna, yellowfin fillet, baked
4.00 oz
(113.40 grams)

Calories: 147
GI: very low

NutrientDRI/DV

 selenium223%

 vitamin B3156.4%

 vitamin B12110.8%

 vitamin B669.4%

 protein66.1%

 phosphorus53.9%

 vitamin D23.2%

 choline20.7%

 potassium17%

 vitamin B112.5%

 vitamin B212.3%

 magnesium11.9%

This chart graphically details the %DV that a serving of Tuna provides for each of the nutrients of which it is a good, very good, or excellent source according to our Food Rating System. Additional information about the amount of these nutrients provided by Tuna can be found in the Food Rating System Chart. A link that takes you to the In-Depth Nutritional Profile for Tuna, featuring information over 80 nutrients, can be found under the Food Rating System Chart.
Health Benefits
Description
History
How to Select and Store
Tips for Preparing and Cooking
How to Enjoy
Individual Concerns
Nutritional Profile
References
Health Benefits



Anti-Inflammatory and Antioxidant Benefits

No single category of nutrient has been more clearly determined to have anti-inflammatory health benefits than omega-3 fatty acids, and tuna is equally well-established as an important food source of omega-3s. In an average 5-ounce can of tuna, you are likely to get about 7-28 milligrams of EPA (eicosapentaenoic acid) and 140-850 milligrams of DHA (docosahexaenoic acid). Both EPA and DHA are critical omega-3 fatty acids for proper regulation of the body's inflammatory system and prevention of excessive inflammation. Generally speaking, you're likely to get more omega-3s from canned albacore than from canned "light" tuna made from other species of tuna like skipjack (but also at times including yellowfin, tongol, or bigeye). But you are also likely to get more mercury from canned albacore as well because albacore are typically larger and older, having had more opportunity to accumulate mercury from contaminated ocean waters.

Researchers in the Department of Marine Science at Coastal Carolina University in Conway, South Carolina have recently taken a very interesting approach to this controversial trade-off between the beneficial, anti-inflammatory omega-3s found in fish and their undesirable contamination with mercury. These researchers reviewed nutritional studies on the anti-inflammatory benefits of omega-3s to arrive at a daily intake recommendation of 500 milligrams for EPA-plus-DHA (combined). Next, they estimated how many servings of fish would be required to meet this recommended level. In the case of canned albacore tuna, for example, they estimated that a person would need to consume 9 servings per month (with 7 ounces per serving) to provide an average daily amount of 500 milligrams of EPA-plus-DHA.

Using a similar type of logic, they then took the National Academy of Sciences (NAS) recommended safe dose level for mercury, calculated a safe daily intake level of mercury from fish of 6.8 micrograms and estimated how many daily fish servings a person could consume without going over this 6.8 microgram limit. In the case of canned albacore tuna, they determined that only 3 servings of canned albacore tuna could be eaten each month if a person wanted to stay below the 6.8 microgram daily limit for mercury. Based on this logic, they concluded that canned albacore tuna did not provide a good trade-off between omega-3s and mercury since a person would need 9 servings per month to meet the omega-3 recommendation, but would actually have to stop after 3 servings in order to stay below the mercury limit. In fact, these researchers did not find any type of tuna (not only canned albacore, but also canned light tuna and wild ahi tuna) that was able to meet the omega-3 recommendation without exceeding the mercury limit. They did find other fish, however, that provided the desired amount of omega-3s without going over the mercury limit. These other fish included salmon, trout, shrimp and tilapia.

While we admire the creativity and logic used by these researchers to evaluate the trade-off between omega-3s and mercury in fish, we take a somewhat different approach while using their same logic. Like these marine science researchers, we think it's important for individuals to minimize their food exposure to mercury, and we like the idea of staying below the NSA limit. However, we also believe there is no reason for a person to depend exclusively on fish for their omega-3s, nor do we believe that all of a person's omega-3s must be provided in the form of EPA and DHA.

Many foods can provide small amounts of omega-3s, and other forms of omega-3s (like alpha-linolenic acid, found in many plant foods) also help to provide us with anti-inflammatory benefits. For these reasons, we believe that individuals have the flexibility to enjoy tuna and other types of fish by focusing on their overall diet and making sure they get plenty of anti-inflammatory omega-3s from all of their foods combined, while still staying below the mercury limit in their overall diet. From a practical standpoint, this approach means including a variety of omega-3 foods in the overall diet, emphasizing fish that are lower in mercury contamination, and including higher mercury fish on a more limited basis. Wild-caught Alaskan salmon, for example, could be eaten during the same week as tuna to help avoid excessive mercury exposure while still reaping the anti-inflammatory benefits of omega-3s.

While small amounts of antioxidant nutrients like vitamin C, manganese, and zinc are provided by tuna, it is unusually rich in one particular antioxidant mineral, namely, selenium. This antioxidant is not only concentrated in tuna but is also present in an unusual form called selenoneine. Selenoneine is especially helpful to the tuna as a nutrient for protecting their red blood cells from free radical damage. Interestingly, it is also able to bind together with mercury compounds in the fish's body (including methylmercury, or MeHg) and lower their risk of mercury-related problems. Because there are approximately 2-3 milligrams of selenoneine in a 4-ounce serving of tuna, we are likely to get some of this same antioxidant protection whenever we eat tuna. Equally interesting, tuna may turn out to be a fish that - even when contaminated with mercury—might pose less of a mercury risk to humans than might otherwise be expected due to the presence of selenium in this special form of selenoneine.

When you steam or sear or broil fresh tuna at home, this cooking process may also result in some special antioxidant benefits. These benefits are related to the presence of small protein fragments—called peptides—that may get formed during the cooking process when proteins in the tuna get broken down. Recent studies have shown that some of the protein breakdown products in tuna have strong antioxidant properties, including the ability to protect cell membranes from oxygen-related damage (a process called lipid peroxidation).

Other Health Benefits

When researchers study the overall benefits of omega-3 containing fish in a regular diet plan, they almost always find cardiovascular benefits to emerge at the top of the health benefit list. Researchers know, for example, that consumption of omega-3 fish can increase the presence of omega-3s in the membranes of red blood cells as well as cells along the blood vessel linings. This increased level of omega-3s in the circulatory system is associated with better regulation of blood pressure and lower risk of blood vessel "clogging." Approximately 2-3 servings of omega-3 fish per week over the course of 3-4 months has been shown to provide these cardiovascular benefits, and in some studies, tuna has specifically been shown to raise bloodstream levels of omega-3s as described above.

Health benefits from tuna may also exist in the area of cancer risk. Here the research is somewhat mixed, for several reasons. First, there is very little research specific to tuna. Most of the large-scale studies have looked at fish intake overall, or fatty versus nonfatty fish, rather than tuna per se. Second, not all researchers classify tuna in the same way. Some classify it as a fatty fish, yet other classify it as a white fish (and non-fatty). Part of the reason for this inconsistency involves widespread consumption of canned albacore tuna, which typically contains less than 3 grams of total fat per ounce. In the area of colon cancer, there is clear evidence that increased intake of omega-3 fats from fish as a group can lower risk of this cancer type. While this fish group has almost always contained tuna in large-scale research studies, we're not aware of studies in which tuna has not been analyzed independently as a unique fish for helping lower colon cancer risk. In the areas of prostate cancer and renal cancer, there is also some evidence of decreased risk from consumption of fish containing omega-3s, although the findings seem to be more mixed for these cancer types, with some studies failing to show decreased risk.

It's worth adding that despite the relative absence of evidence regarding specific intake of tuna and cancer risk, there is a large amount of research connecting decreased overall cancer risk with increased intake of omega-3 fatty acids in the overall diet.



From an overall nutritional standpoint, tuna is more diverse in its nutrient content than many people would suspect. It's an excellent source of vitamin B3 (niacin), and a very good source of other B vitamins including B6 (pyridoxine) and B1 (thiamin). Tuna is also a good source of the minerals phosphorus, potassium, and magnesium. Of course, because of its muscle content, tuna is an excellent source of protein, providing two thirds of the Daily Value (DV) in one 4-ounce serving. As we've previously discussed, it's also a very valuable source of the omega-3 fatty acids EPA and DHA as well as the antioxidant mineral selenium.

Description

The tuna family is a diverse family of fish. Some tuna are classified as "pelagic" fish that live relatively close the surface or in water columns that extend downward for several hundred meters at most. Others are classified as "midwater" fish that can be found at depths up to 600 meters. Tuna swim in most of the world's oceans. For example, there are six major stocks of albacore tuna, in the North Atlantic, South Atlantic, Indian Ocean, Mediterranean Sea, north Pacific and south Pacific.

This family of fish ranges widely in size. Some tuna - like bullet tuna - average about 1 foot in length. Other tuna—like Atlantic Bluefin—average over 6 feet in length and have been known to reach a size of 15 feet. Most tuna migrate over many miles of water (for example, some regularly cross the Atlantic or Pacific Oceans, over a distance of many thousand miles). While some smaller species of tuna live no longer than 3-5 years, it is not unusual for larger species like bluefin to live upwards of 20 years. All tuna belong to the scientific family called Scombridae, which also includes mackerel and bonito.

Among the most commercially popular of all tuna species are the following:

Albacore (Thunnus alalunga)

Albacore are a moderately sized and moderately long-lived species of tuna, with a common length of 3-4 feet, common weight of 15-45 lbs., and an average lifespan of 9-12 years. Albacore tuna can be labeled as "white meat" tuna when canned and has become a popular canned variety in the U.S. From a sustainability perspective, the Monterey Bay Aquarium Seafood Watch ranks canned albacore tuna as a "Best Choice" when caught by pole-and-line or by trolling in the U.S. Pacific or Canadian Pacific Ocean. Other stocks of albacore tuna swim in the North Atlantic, South Atlantic, Indian Ocean, and Mediterranean Sea.

Bigeye (Thunnus obesus)

While smaller and shorter-lived than bluefin (on average), bigyeye are still considered a large and long-lived species of tuna, able to reach lengths of eight feet or more and often averaging five to six feet. Bigeye are sometimes sold under their Hawaiian name, "ahi." Along with yellowfin and bluefin, some bigeye are also used in sushi and and sashimi and labeled referred to as "maguro." The Monterey Bay Aquarium Seafood Watch ranks bigeye tuna as a "Best Choice" when caught by pole-and-line or by trolling in the U.S. Atlantic.

Blackfin (Thunnus atlanticus)

Blackfin tuna belong to the yellowfin subgroup of tuna but have not become a commercially important species, unlike their yellowfin counterparts. Blackfin are relatively small in size, averaging between 1-3 feet in length and often 10-20 lbs.

Bluefin (Thunnus maccoyii—Southern Bluefin; Thunnus orientalis—Pacific Bluefin; and Thunnus thynnus—Atlantic Bluefin)

Bluefin are the largest of the commercial tuna species and can reach weights exceeding 1,000 pounds and lengths of nearly 15 feet. It is also common for bluefin to have a lifespan of 20 years, and in some cases, nearly twice that long. Bluefin are a popular species of tuna in preparation of sushi and sashimi, where they are often referred to as "hon maguro." You can also find bluefin tuna being referred to as "toro" (tuna belly) when served as sushi. Due to their larger size and longevity, bluefin also average higher mercury concentrations than most other species of tuna.

Bluefin are also some of the most endangered tuna species. The International Union for Conservation of Nature (IUCN) in Cambridge, UK lists Southern bluefin as "critically endangered" and Atlantic Bluefin as "endangered." Largely due to these environmental concerns, the Monterey Bay Aquarium Seafood Watch has also recommended avoidance of all bluefin tuna.

Skipjack (Katsuwonus pelamis)

Skipjack is the species of tuna that you are most likely to find in a can of "light" tuna. They're a relatively small species of tuna, often weighing between five to six pounds and averaging one to two feet in length. Skipjack are also shorter lived, with a lifespan of two to three years. This combination of lifestyle circumstances also tends to make skipjack a tuna species that is lower in mercury accumulation.

Skipjack is most often sold as canned light tuna and is the most common species found in tuna cans. It's also sold fresh or frozen.

When prepared for sushi, skipjack tuna is sometimes referred to as "bonito" or "katsuo," and skipjack tuna is often used similarly to yellowfin tuna in preparation of sashimi. Some segments of the sashimi market prefer skipjack and use it interchangeably with yellowfin tuna in grilled or fried preparations.

The Monterey Bay Aquarium Seafood Watch ranks skipjack tuna as a "Best Choice" when caught by pole-and-line or by trolling in any region of the world.



Tongol (Thunnus tonggol)

Tongol (also called longtail) has become a popular alternative species of tuna in the canned "light" tuna market. Unlike many of its fellow tuna, tongol are less migratory, seasonal, and found primarily in the Indian and Western Pacific oceans. Virtually all commercially available tongol come from the coastlines of Malaysia, Indonesia, Thailand, and Iran (where the Indian Ocean becomes the Arabian Sea). Tongol are relatively small in size, averaging approximately 10-12 pounds and ranging from 1-3 feet in length. The overall lifestyle and size of tongol also make them lower in mercury accumulation in the limited data that we have seen. Although most canned light tuna features skipjack as its primary species, it's becoming more and more common to find "light" canned tuna that include tongol. The Monterey Bay Aquarium Seafood Watch does not rank tongol tuna as a "Best Choice." Yet, it does consider it a "Good Alternative" to other tuna types when caught by any method in Malaysia or when caught by pole-and-line or by trolling in Indonesia, Iran, or Thailand.

Yellowfin (Thunnus albacares)

Yellowfin are moderate-to-large sized tuna, ranging widely in size from one to two feet to as large as five to six feet, and in some cases, even longer. Smaller yellowfin average 10-12 pounds in weight, but larger yellowfin will average much more, in the range of 40-60 pounds (and in some cases, even more). Yellowfin are relatively fast growing and have an average lifespan of four to eight years. Their variable size also makes them variable in mercury accumulation, but most of the data we have seen on yellowfin show their mercury concentrations to fall at the moderate level. From a sustainability perspective, Monterey Bay Aquarium Seafood Watch ranks yellowfin tuna as a "Best Choice" when caught by pole and line or trolling in the U.S. Atlantic or Pacific Oceans.

Other Species of Tuna

Other species of tuna include bullet tuna (Auxis rochei), dogtooth tuna (Gymnosarda unicolor), slender tuna (Allothunnus fallai), frigate tuna (Auxis thazard), and kawakawa (Euthynnus affinis).

History

The evolution of ocean fish shows the emergence of tuna to have occurred approximately 45 millions years ago—long before humans were around to go fishing for them! Tuna swim in all of the earth's oceans (except for oceans at the North and South Poles), including all parts of the Atlantic, Pacific, and Indian Oceans, as well as the Mediterranean Sea. There is evidence of Phoenician trap fisheries for tuna as early as 2000 BC.

For most of human history, fishing for tuna has been a small-scale regional and seasonal practice. The unique migratory patterns of tuna made small coastal fisheries for tuna the rule rather than the exception. Beginning in the 1940's and 1950's, however, industrial fishing for tuna started to become more and more widespread, with greatly expanded tonnage and offshore distances.

Even more recently, seafood production has witnessed the expansion of tuna farming. The farming of finfish like tuna in an open sea environment typically relies on the use of net pens to contain the fish. For example, a recent journal study using Google Earth documented the existence of 248 net pens for tuna in the Mediterranean alone.

How to Select and Store

Tuna is sold in many different forms. It is available fresh as steaks, fillets, or pieces. Tuna is probably best known in its canned form.

Just as with any seafood, it is best to purchase fresh tuna from a store that has a good reputation for having a frequent supply of fresh fish. Get to know a fishmonger (the person who sells the fish) at the store, so you can have a trusted resource from whom you can purchase your fish with confidence.

Fresh whole tuna should be displayed buried in ice, while fillets and steaks should be placed on top of the ice. Try to avoid purchasing tuna that has dry or brown spots.

Smell is a good indicator of freshness. Since a slightly "off" smell cannot be detected through plastic, if you have the option, purchase displayed fish as opposed to pieces that are prepackaged. Once the fishmonger wraps and hands you the fish that you have selected, smell it through the paper wrapping and return it if it has a truly strong fishy odor.

Canned tuna is available either solid or in chunks, and is packaged in oil, broth or water. Although the tuna packed in oil is usually the moistest, it also has the highest fat content, and the oils in which it is packed are high in omega-6 fats. Since omega-6s and omega-3s compete for the same enzymes that activate them for use in the body, and most Americans already consume too many omega-6 fats in comparison to omega-3s, it is best to purchase tuna packed in water or broth. Oftentimes, canned tunas do not distinguish which specific species was used except to note that it is either light tuna (bluefin or yellowfin) or white tuna (usually albacore).



When storing all types of fresh seafood, including tuna, it is important to keep them cold since fish spoils quickly and is very sensitive to temperature. Therefore, after purchasing tuna or other fish refrigerate it as soon as possible. If the fish is going to accompany you during a day full of errands, keep a cooler in the car where you can place your tuna to make sure it stays cold and does not spoil.

The temperature of most refrigerators is slightly warmer than ideal for storing fish. To ensure maximum freshness and quality, it is important to use special storage methods to create the optimal temperature for holding the fish. One of the easiest ways to do this is to place fish, which has been well wrapped, in a baking dish filled with ice. The baking dish and fish should then be placed on the bottom shelf of the refrigerator, which is its coolest area. Replenish the ice one or two times per day.

The length of time that tuna can stay fresh stored this way depends upon how fresh it is, i.e. when it was caught. Fish that was caught the day before you purchased it can be stored for about four days, while fish that was caught the week before can only be stored for about one or two days.

You can extend the shelf life of tuna by freezing it. To do so, wrap it well in plastic and place it in the coldest part of the freezer where it will keep for about two to three weeks.



All of these selection and storage steps for tuna are especially important due to special risk of histamine formation in tuna. Adverse reactions to histamine in tuna are often referred to as "scombrotoxic poisoning" since tuna belong to Scombridae family of fish. Failure to keep fresh tuna well chilled at refrigerator temperatures prior to cooking can result in increased histamine content and greater risk of adverse reaction. So can improper handling of canned tuna, in which a can is opened and allowed to sit at room temperature after being opened yet not consumed for several hours. The possibility of unwanted histamine formation in tuna makes it especially important for you to use care in the selection and storage of this food.

Shrimp

An Important Message About ShrimpWe have placed shrimp on our "10 Most Controversial WHFoods List." This list was created to let you know that even though some foods (like shrimp) can make an outstanding contribution to your meal plan, they are definitely not for everyone. Shrimp can be difficult to find in high-quality form; can be more commonly associated with adverse reactions than other foods; and can present more challenges to our food supply in terms of sustainability. More details about our 10 Most Controversial WHFoods can be found here.

What's New and Beneficial About Shrimp

Shrimp are an unusually concentrated source of the antioxidant and anti-inflammatory nutrient called astaxanthin. It's not unusual for a single 4-ounce serving of shrimp to contain 4 milligrams of astaxanthin. Astaxanthin is a carotenoid that is receiving special attention in the latest health research, primarily for its anti-inflammatory and antioxidant properties. Release of inflammatory messaging molecules (like tumor necrosis factor alpha and interleukin 1B) is suppressed by astaxanthin, and so is unwanted oxidation of fats in immune cells. In animal studies, risk of colon cancer is lowered by intake of astaxanthin, and immune-related problems of diabetes are also reduced. It's the antioxidant and anti-inflammatory properties of astaxanthin that seems to explain these disease-related benefits. Since few commonly consumed fish (with the exception of salmon) can provide us such concentrated amounts of astaxanthin, shrimp may be making a unique health contribution in this way.

At 56 micrograms in every 4 ounces, shrimp is an excellent source of the antioxidant mineral selenium. Recent research studies show that the selenium contained in shrimp can be well-absorbed into the human body. In one study, we've seen an estimate of about 80-85% for total selenium absorption from this shellfish. Since selenium deficiency has been shown to be a risk factor for heart failure and other forms of cardiovascular disease, as well as for other problems including type 2 diabetes, compromised cognitive function, and depression, shrimp may have a unique role to play in your meal plan if your health history places you at special risk in any of these areas.

Shrimp is often included on the "avoid" list for persons wanting to minimize their dietary intake of cholesterol. The 220 milligrams of cholesterol contained in a 4-ounce serving of shrimp makes this approach a legitimate concern. However, despite its high cholesterol content, several recent research studies have noted some desirable aspects of the fat profile in shrimp. One of these desirable aspects is shrimp's omega-3 fat content. Four ounces of shrimp provides about 350-375 milligrams of omega-3 fatty acids, including about 50% EPA (eicosapentaenoic acid) and 50% DHA (docosahexaenoic acid). EPA and DHA are especially important omega-3s for cardiovascular and nervous system health. In addition to this great mixture of omega-3s, shrimp also provides an outstanding ratio of omega-3:omega-6 fats. There are approximately three times as many omega-3s as omega-6s in shrimp. Since higher ratios of omega-3:omega-6 are associated with decreased risk of many chronic diseases—including obesity, high blood pressure, and type 2 diabetes—this aspect of shrimp's fat content is a huge plus. Finally, it is interesting to note that according to recent studies, cholesterol is not the only sterol in shrimp. This type of fat is found in smaller amounts in the form of beta-sitosterol, campesterol, and brassicasterol. While chemically similar to cholesterol, these other sterols function as anti-inflammatory molecules and they are associated with decreased levels of LDL-cholesterol, which would be considered a health benefit by many researchers. When looked at from this broader perspective, risks related to the high cholesterol content of shrimp might be overshadowed by its omega-3 and sterol composition—but we will need future studies to help us understand more about the big picture involving shrimp and fat. As always, if you have concerns that have you need to be cautious about cholesterol intake, discuss the inclusion of shrimp in your diet with your healthcare practitioner.

If you are planning to eat wild-caught, cold-water shrimp, the Monterey Bay Aquarium Seafood Watch has determined that your best overall choices in this category of shrimp are British Columbia spot prawns, California coonstripe shrimp (caught using submerged pots), and Oregon pink shrimp. (You probably won't be able to tell from a label whether your shrimp have been pot-caught, so you will need to talk to your fishmonger or the fishery itself in order to determine this information.)

If you are concerned about environmental consequences when consuming farmed shrimp, the Monterey Bay Aquarium Seafood Watch recommends that you restrict your intake to shrimp that have been raised in a fully re-circulating system. These systems make direct use of filtered seawater or try to recreate the mineral composition of seawater in freshwater. (You will often need to contact the supplier in order to determine whether this type of farming system was used.) Pacific white shrimp (Litopenaeus vannamei) can make an excellent choice when farmed in this way.

While U.S. farmed, freshwater shrimp are not widely available in the marketplace, they are also recommended by the Monterey Bay Aquarium Seafood Watch as a Best Choice when choosing shrimp.

Shrimp, large, steamed
4.00 oz
(113.40 grams)

Calories: 135
GI: very low

NutrientDRI/DV

 selenium102%

 vitamin B1278.3%

 protein51.6%

 phosphorus49.5%

 choline36.1%

 copper32.2%

 vitamin B319%

 zinc16.8%

 vitamin E16.6%

 vitamin B615.8%

 omega-3 fats14.1%

 pantothenic acid11.8%

 vitamin A11.3%

This chart graphically details the %DV that a serving of Shrimp provides for each of the nutrients of which it is a good, very good, or excellent source according to our Food Rating System. Additional information about the amount of these nutrients provided by Shrimp can be found in the Food Rating System Chart. A link that takes you to the In-Depth Nutritional Profile for Shrimp, featuring information over 80 nutrients, can be found under the Food Rating System Chart.

Health Benefits

Description

History

How to Select and Store

Tips for Preparing and Cooking

How to Enjoy

Individual Concerns

Nutritional Profile

References

Health Benefits

Anti-Inflammatory and Antioxidant Support

We don't usually think about seafood as a source of antioxidants, but shrimp features at least two unique antioxidants in its nutrient composition: the xanthophyll carotenoid called astaxanthin, and the mineral selenium.

Astaxanthin

Astaxanthin is the primary color pigment in many shrimp, and it helps provide their tissue with its red and orange shades. While many reddish-orange foods get their color from other carotenoids (or from flavonoids), shrimp are especially concentrated in this one particular type of carotenoid. (Astaxanthin often accounts for at least two-thirds of all carotenoids in shrimp.) It's not unusual for a 4-ounce serving of shrimp to contain 4 milligrams of astaxanthin.

Astaxanthin is a carotenoid that is receiving special attention in the latest health research, primarily for its anti-inflammatory and antioxidant properties. Release of inflammatory messaging molecules (like tumor necrosis factor alpha and interleukin 1B) is suppressed by astaxanthin as is the unwanted oxidation of fats in immune cells. In animal studies, risk of colon cancer is lowered by intake of astaxanthin, and immune-related problems of diabetes are reduced. Since few fish (with the exception of salmon) can provide us with more concentrated amounts of astaxanthin, shrimp is likely to provide us with some unique health benefits in this context.

Selenium

In the world of antioxidants, few enzymes are more important in our body than glutathione peroxidase (GPO). GPO helps protect most of our body systems from unwanted damage by oxygen-containing molecules. It is critical in body systems like the lungs, where exposure to these molecules is especially high. GPO is an enzyme that cannot function without the mineral selenium.

At 45 micrograms in every 4 ounces, shrimp is an excellent source of this antioxidant mineral. Shrimp is not only rich in selenium; research studies show that the selenium found in shrimp can be well-absorbed into the human body. In one study, we've seen an estimate of about 80-85% for total selenium absorption from this shellfish. In addition to risk of problems involving lung function, selenium deficiency has been shown to increase our risk of heart failure and other forms of cardiovascular disease, as well as for other problems including type 2 diabetes, compromised cognitive function, and depression. If your health history places you at special risk in any of these areas, shrimp may be an especially valuable food in your meal plan due to its selenium content.

Protein and Peptide Support

At 6 grams per ounce, shrimp is very good source of protein. In fact, among all WHFoods, shrimp ranks as our 8th best source of high-quality protein! The protein richness of shrimp is one of the reasons this shellfish is relied on in so many different culinary traditions.

When the protein in fish is broken down during digestion, smaller protein fragments called peptides are formed. Recent research studies have shown that many of these peptides have unique properties, including the ability to stimulate release of the hormone cholecystokinin (CCK) from cells that line our intestinal tract. Release of CCK is important for many reasons, including the role of CCK in regulating appetite. Our feeling of satiety (lack of appetite) is partly related to the levels of CCK in our digestive tract. By helping trigger release of CCK, shrimp peptides may play a role in helping us feel full. In the long run, this feeling of satiety may also be an advantage in helping to decrease our risk of obesity. Research on shrimp peptides and satiety is in its early stage, and largely limited to animal studies at this point. But we expect to see increasing interest in this area of shrimp and health.

Other Health Benefits

At a mere 7 calories per shrimp, we can eat a relatively large amount of shrimp without using up too many of our daily calories. For example, a person eating 1,800 calories per day could consume 20 shrimp and only be "spending" about 8% of his or her daily calories. This very low calorie cost would not be so remarkable if it were not for the fact that shrimp provides us with significant amounts of so many nutrients. We usually have to eat foods with a far greater calorie content to get the nutrient richness provided by shrimp. For example, those same 20 shrimp that provide us with about 140 calories also provide us with 25 grams of protein, almost 2 mcg of vitamin B12, as well as contributing minerals such as copper, magnesium, phosphorus, and zinc. In addition to vitamin B12, shrimp also provides us with most other B vitamins—such as niacin, choline, vitamin B6, and pantothenic acid—in significant amounts. The overall nutrient richness of shrimp gives it the ability to help balance out our nutrient intake in a wide variety of areas.

Description

Shrimp are crustaceans (just like lobsters and crabs) and they belong to a category of living things called arthropods. Like all arthropods, shrimp have their skeleton on the outside instead of the inside (it's called an exoskeleton) and this outer skeleton is one of the features that gives shrimp their unusual look - almost like having a head shield that blocks out all of their features except their eyes, mouth opening, and antennae. In the U.S., consumers don't typically eat the outer skeleton, heads, or tails of shrimp, even though these parts are often rich in nutrients and commonly consumed in other countries. Shrimp accounts for about 25% of all seafood sold in the United States.

The terms "shrimp" and "prawns" can be confusing. Even scientists often use these words inconsistently. In the popular press and in many restaurants, larger shrimp—often from freshwater habitats—are referred to as "prawns," while smaller shrimp—often from saltwater habitats—are called "shrimp." In terms of size, "large" typically means that you get about 40 or less per cooked pound (in comparison to about 50 for "medium" and 60 for "small"). But from a science perspective, both shrimp and prawns can come from saltwater or freshwater, and there is no absolute standard for measuring small, medium, or large. In this article and throughout our website, we'll be using the word "shrimp" as a general term that includes all species—even those which might be referred to as "prawns" in some research studies or in some restaurants.

Many people ask about the way shrimp sizes (small, medium, large, jumbo) are determined. While there is no precise method typically used for shrimp sizing, count per pound is the most common method used. (Count per pound refers to the number of shrimp that you get when you purchase or consume one pound.) With small cooked shrimp, that number is usually around 60. With medium cooked shrimp, it falls to about 50 (since the shrimp are bigger, and each one weighs more). For large shrimp, the count per pound is about 40. For jumbo shrimp the count per pound is about 30.

Traditionally, shrimp have grouped together into categories based on their natural habitats. Warm-water shrimp come from tropical waters in southern parts of the world, and cold-water shrimp come from northern climates. Many warm-water shrimp belong to one specific family called Penaeidae. Tiger prawns, tiger shrimp, and Indian prawns are members of this family. Many cold-water shrimp belong to a second family called Pandalidae. Spot shrimp, striped shrimp, dock shrimp, humpback shrimp, Northern shrimp, and Northern prawns are members of this second family. You'll find white shrimp, pink shrimp, and brown shrimp that come from both water-warm and cold-water regions.

Both warm-water and cold-water shrimp belonging to these two families are saltwater shrimp. They are found in many of the world's oceans and seas, where they are typically caught by trawling.

Freshwater shrimp is a third category based on habitat. Just like the name implies, freshwater shrimp are not native to oceans and seas but to non-salt waters including lakes, rivers, and streams. Freshwater shrimp belong to a scientific category of living things (infraorder) called Caridea.

Unfortunately, the traditional ways of classifying shrimp listed above are no longer adequate for understanding shrimp in the marketplace due to the quick rise of shrimp farming and globalization of the food supply. It's become common for shrimp to be removed from their native habitat and raised in farm settings that don't always resemble their native conditions. Today, the vast majority of shrimp available in U.S. groceries are farmed shrimp, and the quick rise in shrimp farming has raised concerns among many consumers about the health safety and environmental safety of shrimp. For more information about these concerns, please see our Individual Concerns section.

As described above, it's possible to find white shrimp, pink shrimp, and brown shrimp that are native to warmer southern waters as well as older northern ones. However, the flesh of virtually all shrimp—when cooked—turns a vibrant shade of pink.

History

Shrimp and other shellfish were enjoyed in the world's Mediterranean region during the early centuries AD. Classical Greek and Roman texts include shrimp recipes and descriptions of fishing practices. During most of shrimp's culinary history, farming was not used as a method of shrimp production. Shrimp were caught in pots or traps—not only by hand, but also in relatively small amounts. During certain periods of history, the labor-intensive nature of shrimp fishing turned shrimp into a delicacy that was both rare and costly.

Beginning in the 1400-1500's, trawling became a more widespread method for catching shrimp. Trawling refers to the attachment of a large net behind a fishing boat (trawler) that gets dragged through the water as a means of trapping the fish. Shrimp trawlers became a way of catching more shrimp more quickly, and with less manpower. However, large nets ended up trapping other sea creatures, not just shrimp. This problem—which became known as "by-catch"—continues to this day. For example, in 1989, the U.S. Congress passed a law banning the import of wild-caught shrimp from Thailand because Thai shrimp trawlers had failed to install turtle excluder devices (TEDs) that could help prevent sea turtles from getting caught up in the fishing nets.

Beginning in the 1970's, a new trend began to emerge in the shrimp industry. This new trend was shrimp farming. Many factors led to the development of shrimp farming, including depletion of wild shrimp stock, technological developments in aquaculture (the raising of fish in containment facilities), globalization of the food supply, and economic opportunities associated with large-scale shrimp production. In what has been called the "Blue Revolution," world production of shrimp went from 25,000 metric tons in the 1970's to more than 750,000 metric tons in less than two decades. Today there are more than 25,000 shrimp farms in Thailand alone, and shrimp farms line the coastal areas of many Asian countries, including Vietnam, Indonesia, and China. India, Myanmar (Burma), Bangladesh, Australia, and the Philippines are also important shrimp farming countries, as are the Central American countries of Ecuador, Guatemala, and Honduras as well as the South American countries of Colombia, Venezuela, and Peru. In North America, Canada, Mexico, and the United States also produce important amounts of farmed shrimp. Many individuals have concerns about the consequences of shrimp farming for the environment as well as for human health. For more information about these concerns, please see our Individual Concerns section.

How to Select and Store

Just as with any seafood, it is best to purchase shrimp from a store that has a good reputation for having a fresh supply. Get to know a fishmonger (person who sells the seafood) at the store so that you can have a trusted resource from whom you can purchase your seafood.

When you will be preparing the shrimp should influence your decision as to whether you should buy fresh or frozen shrimp. Frozen shrimp offer the longest shelf life, as they are able to be kept for several weeks, whereas fresh shrimp will only keep for a day or two. We think about fresh shrimp as a very perishable food, ideally eaten on the same day as they are purchased.

Fresh shrimp should have firm bodies that are still attached to their shells. They should be free of black spots on their shell since this indicates that the flesh has begun to break down. In addition, the shells should not appear yellow or gritty as this may be indicative that sodium bisulfate or another chemical has been used to bleach the shells.

Smell is a good indicator of freshness; good quality shrimp have a slightly saltwater smell. Since a slightly "off" smell cannot be detected through plastic, if you have the option, purchase displayed shrimp as opposed to those that are prepackaged. Once the fishmonger wraps and hands you the shrimp that you have selected, smell them through the paper wrapping and return them if they do not smell right. When fresh shrimp have been left out for too long, some people describe them as having an "ammonia" smell.

Color can also be an indicator of poor fresh shrimp quality. Unless you are purchasing spotted or striped shrimp, you should not see dark spots or rings of any kind. These markings are usually a sign of deterioration.

When storing any type of seafood, including shrimp, it is important to keep it cold since seafood is very sensitive to temperature. Therefore, after purchasing shrimp or other seafood, make sure to return it to a refrigerator as soon as possible. If the shrimp is going to accompany you during a day full of errands, keep a cooler in the car where you can place the shrimp to make sure it stays cold and does not spoil.

The temperature of most refrigerators is slightly warmer than ideal for storing seafood. Therefore, to ensure maximum freshness and quality, it is important to use special storage methods so as to create the optimal temperature for holding the shrimp.

One of the easiest ways to do this is to place the shrimp in a zip-lock bag in a baking dish layered with ice or icepacks. Place ice or icepacks over the shrimp as well. The baking dish and shrimp should then be placed on the bottom shelf of the refrigerator, which is its coolest area. Replenish ice one or two times per day. Shrimp can be refrigerated for up to two days although it should be purchased as close to being served as possible.

You can extend the shelf life of shrimp by freezing it. To do so, wrap it well in plastic and place it in the coldest part of the freezer where it will keep for about one month.

To defrost shrimp place it in a bowl of cold water or in the refrigerator. Do not thaw the shrimp at room temperature or in a microwave since this can lead to a loss of moisture and nutrients, and can increase risk of contamination.

Scallops

The soft fleshy texture and delicately mild sweet flavor of scallops are enjoyed by even those who are not particularly fond of fish or other shellfish. The season for fresh sea scallops and bay scallops runs from October through March, while fresh calico scallops are available from December through May. Sea scallops and frozen scallops are available year-round.

Scallops are mollusks that have two beautiful convexly ridged, or scalloped, shells. They consist of two shells hinged at one end which is why they are known to marine biologists as bi-valve mollusks. The edible portion of the scallop is the white muscle that opens and closes the two shells and is called the "nut." The reproductive glands known as "coral" are also edible, although not widely consumed in North America. 

Scallops, steamed
4.00 oz
(113.40 grams)

Calories: 126
GI: low

NutrientDRI/DV

 vitamin B12101.6%

 phosphorus69%

 protein46.5%

 selenium44.7%

 choline29.5%

 zinc16%

 magnesium10.4%

 potassium10.1%

This chart graphically details the %DV that a serving of Scallops provides for each of the nutrients of which it is a good, very good, or excellent source according to our Food Rating System. Additional information about the amount of these nutrients provided by Scallops can be found in the Food Rating System Chart. A link that takes you to the In-Depth Nutritional Profile for Scallops, featuring information over 80 nutrients, can be found under the Food Rating System Chart.

Health Benefits

Description

History

How to Select and Store

Tips for Preparing and Cooking

How to Enjoy

Individual Concerns

Nutritional Profile

References

Health Benefits

Most people know that fish is good for you, but what about other seafood? As it turns out, scallops, in addition to their delectable taste, contain a variety of nutrients that can promote your cardiovascular health, plus provide protection against colon cancer.

A Nutrient Team for Better Cardiovascular Health

Scallops are actually an excellent source of a very important nutrient for cardiovascular health, vitamin B12. Vitamin B12 is needed by the body to convert homocysteine, a chemical that can directly damage blood vessel walls, into other benign chemicals. Since high levels of homocysteine are associated with an increased risk for atherosclerosis, diabetic heart disease, heart attack, and stroke, it's a good idea to be sure that your diet contains plenty of vitamin B12 to help keep homocysteine levels low (homocysteine is also associated with osteoporosis, and a recent study found that osteoporosis occurred more frequently among women whose vitamin B12 status was deficient or marginal compared with those who had normal B12 status.)

In addition to their B12, scallops are a good source of magnesium and potassium, two other nutrients that provide significant benefits for the cardiovascular system. Magnesium helps out by causing blood vessels to relax, thus helping to lower blood pressure while improving blood flow. Potassium helps to maintain normal blood pressure levels.

Increases Heart Rate Variability—A Measure of Heart Muscle Function

One of the ways in which consuming fish rich in omega-3 fats, such as scallops, promotes cardiovascular health is by increasing heart rate variability (HRV), a measure of cardiac function, in as little as three weeks, according to a study published in the April 2005 issue of Chest.

By providing greater variability between beats, the marine omega 3 fatty acids, EPA and DHA, reduce the risk of arrhythmia and/or sudden death.

Researchers from Atlanta, GA, Boston, MA, and Cuernavaca, Mexico, took the HRV of 58 elderly patients every other day for two months to establish an HRV baseline for each participant. For the next 11 weeks, half of the study participants took a daily 2 gram supplement of fish oil and the other half took a daily 2 gram supplement of soy oil.

Patients in both groups experienced a significant increase in HRV, with those who took fish oil achieving a greater increase in a shorter time period. Patients who received fish oil experienced increased HRV within the first 2.7 weeks, whereas it took 8.1 weeks for a significant increase in HRV to be seen in the group taking soy oil.

On the other hand, while none of the study participants experienced significant negative side effects, 41% of participants in the fish oil group reported belching, compared to 16% in the soy oil group.

"Our findings contradict the current belief in the medical community that increasing the intake of omega-3 fatty acids produces only long-term cardiac benefits," said the study's lead author, Fernando Holguin, MD, Emory University School of Medicine, Atlanta, GA. "In fact, our study group showed improvements in heart function in as little as two weeks."

"Studies like this demonstrate that there are additional approaches we can take to protect ourselves from heart attacks," said Paul A. Kvale, MD, FCCP, President of the American College of Chest Physicians. "It's exciting to see the potential for omega-3 fatty acids in improving heart function when it complements a healthy lifestyle of exercising, maintaining a healthy weight, and getting eight hours of sleep." We'd add eating healthful foods to this proactive list. Rather than pop a daily pill, we'd rather enjoy a daily "dose" of delicious scallops, soyfoods, or tuna. For recipes certain to not only increase your heart rate variability but also your delight in eating, click Recipes.

Protection against Fatal Heart Arrhythmia

A healthy way of eating that includes at least 10 ounces of omega-3-rich fish each week improves the electrical properties of heart cells, protecting against fatal abnormal heart rhythms, suggests a study from Greece.

"Long-term consumption of fish is associated with lower QT interval in free-eating people without any evidence of cardiovascular disease. Thus, fish intake seems to provide anti-arrhythmic protection at a population level," wrote the authors in the American Journal of Clinical Nutrition. (Chrysohoou C, et al.)

The QT interval is a measure of the heart's electrical cycle, from the beginning of ventricular depolarization, the Q wave, to the end of the T wave, at which point cardiac repolarization is complete.

A lower QT score indicates a lower resting heart rate. As a higher resting heart rate has been linked to an increased risk of sudden death, the result of approximately 50% of heart attacks, lowering the resting heart rate provides significant health benefit.

Researchers at the University of Athens enrolled 3,042 people (1,514 men, aged 18-87, and 1,528 women, aged 18-89), who used a validated food frequency questionnaire to record their food intake of 156 different foods. Along with alcohol consumption and physical activity were also recorded, and electrocardiography was used to measure several indexes of study participants' heart rate.

After the raw data scan, those who ate more than 10 ounces (300 grams) of fish per week were found to have QT scores 13.6% lower than people who did not eat fish.

After adjusting the results for potentially confounding factors such as age, sex, physical activity status, BMI, smoking habits and intake of nuts, the reduction in QT scores in those eating 10 or more ounces of fish each week rose to 29.2%, compared to those who did not eat fish.

In an earlier study, Harvard researchers reported that among those consuming the most fish, heart rate was 2.3 beats per minute lower and likelihood of prolonged QT was 46% lower. Similar results were found in study participants taking 1 gram of omega-3s daily. The mechanism behind these benefits is thought to be omega-3 fats' effects on the flow of sodium and calcium in the ion channels, which are involved with electrical signaling in cells. Practical Tip: A typical serving of fish is 4 ounces, so just 3 servings of omega-3-rich fish, such as scallops, each week would provide 2 ounces more than the 10 ounces this research indicates confers significant protection against sudden death from a heart attack. For great, quick and easy recipe ideas, take a look at our Recipe Assistant.

Protection against Stroke

Eating fish, such as scallops, as little as 1 to 3 times per month may protect against ischemic stroke (a stroke caused by lack of blood supply to the brain, for example, as a result of a blood clot), suggests a meta-analysis of 8 studies published in the July 2004 issue of Stroke.

Data on nine independent groups participating in eight different studies found that, compared to those who never consumed fish or ate fish less than once per month, risk of ischemic stroke dropped:

9% in those eating fish 1 to 3 times per month

13% in those eating fish once per week

18% in those eating fish 2 to 4 times per week

31% in those eating fish 5 or more times each week

Eating Fish Daily Provides Substantially More Protection against Heart Attack

While as little as a weekly serving of fish lowers risk of ischemic stroke, enjoying a daily serving omega-3-rich fish, such as scallops, provides significantly greater reduction in the risk of coronary heart disease than eating fish even as frequently as a couple of times a week, show the findings of a study published in the January 17, 2006 issue of Circulation, the journal of the American Heart Association.

Researchers in Japan followed 41,578 men and women aged 40 to 59, none of whom had cardiovascular disease or cancer when the study began, from 1990-1992 to 2001. Food frequency questionnaires completed at the beginning of the study and in 1995, provided information on weekly fish intake, which was analyzed for omega-3 content.

When individuals whose fish consumption was in the top one-fifth of participants at 8 times per week were compared to those whose intake was in the lowest fifth at once per week, they were found to have a 37% lower risk of developing coronary heart disease and a 56% percent lower risk of heart attack.

When the effect of omega-3 fatty acid intake on cardiovascular risk was analyzed, coronary heart disease risk was lowered by 42% among those whose intake was the highest at 2.1 grams per day or more compared to those whose intake was the lowest at 300 milligrams per day. Those whose intake of omega 3s was in the top fifth received a 65% reduction in the risk of heart attack compared to those whose omega 3 intake was lowest.

The authors theorize that daily fish consumption is highly protective largely due to the resulting daily supply of omega-3 fatty acids, which not only reduce platelet aggregation, but also decrease the production of pro-inflammatory compounds called leukotrienes. Lowering leukotrienes reduces damage to the endothelium (the lining of the blood vessels), a key factor in the development of atherosclerosis.

"Our results suggest that a high fish intake may add a further beneficial effect for the prevention of coronary heart disease among middle-aged persons," note the study's authors.

Choose Broiled or Baked, but Not Fried Scallops to Reduce Risk of Atrial Fibrillation (Heart Arrhythmia)

Eating scallops that are broiled or baked, but not fried, may reduce risk of atrial fibrillation, the most common type of heart arrhythmia, especially in the elderly, according to a Harvard study published in the July 2004 issue of Circulation. In the 12-year study of 4,815 people 65 years of age or older, eating canned tuna or other broiled or baked fish 1 to 4 times a week correlated with increased blood levels of omega-3 fatty acids and a 28% lower risk of atrial fibrillation. Eating broiled or baked fish 5 times a week lowered risk even more—a drop in atrial fibrillation risk of 31%. Eating fried fish, however, provided no similar protection. Not only is fried fish typically made from lean fish like cod and Pollack that provide fewer omega-3 fatty acids, but in addition, frying results in the production of damaged, free-radical-laden fats in the fish as well as the frying oil.

In further research to determine if the omega-3 fats found in fish oil were responsible for fish's beneficial effects on the heart's electrical circuitry, Dariush Mozaffarian and colleagues from Harvard Medical School analyzed data on fish intake and electrocardiogram results from 5096 adults, aged 65 or older, who were enrolled in the Cardiovascular Health Study from 1989-1990.

Eating tuna or other broiled or baked fish at least once a week was associated with lower heart rate (-3.2 beats/minute) and a 50% lower likelihood of prolonged ventricular repolarisation (the period of time it takes the heart to recharge after it beats, so it can beat again), compared to those consuming fish less than once a month.

Consuming 1 gram/day of omega-3 fatty acids from fish was associated with 2.3 beats/minutes lower heart rate and a 46% lower risk of prolonged ventricular repolarisation. Eating fish at least 5 times per week was associated with an even healthier heart rhythm. However, eating fried fish (typically sold in the U.S. as fish burgers or fish sticks) was not associated with increased blood levels of omega 3 fats or any beneficial electrocardiogram results. In fact, a previous study led by the same researcher (Mozaffarian, Am J Cardiol 2006 Jan) found that while eating baked or broiled fish was linked to a slower but more powerful heart beat and lower blood pressure, eating fried fish was associated with heart muscle motion abnormalities, a reduced ejection fraction, lower cardiac output, and higher blood pressure. Since irregular heart beats are a major precipitating factor in sudden death due to cardiac arrest, promoting a healthy heart rhythm by eating baked or broiled—not fried—fish several times a week makes very good sense. Happily, as our recipes, such as our serving ideas for scallops (immediately below) show, it's a quick, easy and most importantly, delicious prescription.

Fish, Fruit and Vegetables Protective against Deep Vein Thrombosis, Pulmonary Embolism

Deep vein thrombosis is a dangerous condition in which blood clots develop in the deep veins of the legs, thighs or pelvis, causing swelling and pain. An embolism is created if a part or all of the blood clot in the deep vein breaks off from the site where it was created and moves through the venous system. If the clot lodges in the lung, a very serious condition, pulmonary embolism, arises.

Fortunately, a healthy way of eating offers significant protection, as demonstrated by a prospective study over 12 years that involved almost 15,000 middle-aged adults. While those eating the most red and processed meat doubled their risk of deep vein thrombosis (DVT), those in the upper 3 quintiles of fruit and vegetable intake had a 41-53% lower risk of DVT. And those eating fish at least once each week were found to have a 30-45% lower DVT risk. (Steffen LM, Folsom AR, et al.,Circulation.)

Practical Tip: For protection against deep vein thrombosis, increase your consumption of fruit and vegetables; eat fish at least once a week; and decrease consumption of red and processed meats.

Protection Against Cancer

A high intake of vitamin B12 has also been shown to be protective against colon cancer. Vitamin B12 helps to protect the cells of the colon from mutations as a result of cancer-causing chemicals—another good reason to eat plenty of vitamin B12. So add scallops, an excellent source of vitamin B12 and a very good of protein, to your list of healthy seafood and enjoy.

A Canadian study published in Cancer Epidemiology Biomarkers(Fritschi L, Ambrosini GL, et al.) suggests that eating fish frequently may provide serious protection against three types of cancer: leukemia, multiple myeloma, and non-Hodgkin's lymphoma. Researchers compared the diets of almost 3,000 individuals with these cancers to those of 4,200 healthy controls. People who ate the most fish and who got most of their total fat calories from fish were 28% less likely to have leukemia, 36% less likely to have multiple myeloma, and 29% less likely to have non-Hodgkin's lymphoma.

Omega-3-Rich Fish Protective against Colorectal Cancer

A diet rich in the omega-3 fats, which are found in scallops, greatly reduces risk of colorectal cancer, indicates a study comparing 1,455 subjects with colorectal cancer to 1,455 matched healthy controls.

Those whose diets provided the most omega-3s had a 37% reduction in colorectal cancer risk, compared to those whose diets provided the least. Colorectal cancer risk was 41% lower in those with the highest average intake of EPA, and 37% lower in those whose diets supplied the most DHA. (Theodoratou E, McNeill G, et al. Am J Epidemiol.)

Practical Tip: Each of the World's Healthiest Foods' fish is a good to excellent source of omega-3s. Let our Recipe Assistant provide you with delicious, quick ways to add more omega-3s to your healthy way of eating.

Fish and Whole Grains Highly Protective against Childhood Asthma

According to the American Lung Association, almost 20 million Americans suffer from asthma, which is reported to be responsible for over 14 million lost school days in children, and an annual economic cost of more than $16.1 billion.

Increasing consumption of whole grains and fish could reduce the risk of childhood asthma by about 50%, suggests the International Study on Allergy and Asthma in Childhood (Tabak C, Wijga AH, Thorax).

The researchers, from the Dutch National Institute of Public Health and the Environment, Utrecht University, University Medical Center Groningen, used food frequency questionnaires completed by the parents of 598 Dutch children aged 8-13 years. They assessed the children's consumption of a range of foods including fish, fruits, vegetables, dairy and whole grain products. Data on asthma and wheezing were also assessed using medical tests as well as questionnaires.

While no association between asthma and intake of fruits, vegetables, and dairy products was found (a result at odds with other studies that have supported a link between antioxidant intake, particularly vitamins C and E, and asthma), the children's intake of both whole grains and fish was significantly linked to incidence of wheezing and current asthma.

In children with a low intake of fish and whole grains, the prevalence of wheezing was almost 20%, but was only 4.2% in children with a high intake of both foods. Low intake of fish and whole grains also correlated with a much higher incidence of current asthma (16.7%). compared to only a 2.8% incidence of current asthma among children with a high intake of both foods.

After adjusting results for possible confounding factors, such as the educational level of the mother, and total energy intake, high intakes of whole grains and fish were found to be associated with a 54 and 66% reduction in the probability of being asthmatic, respectively.

The probability of having asthma with bronchial hyperresponsiveness (BHR), defined as having an increased sensitivity to factors that cause narrowing of the airways, was reduced by 72 and 88% when children had a high-intake of whole grains and fish, respectively. Lead researcher, CoraTabak commented, "The rise in the prevalence of asthma in western societies may be related to changed dietary habits." We agree. The Standard American Diet is sorely deficient in the numerous anti-inflammatory compounds found in fish and whole grains, notably, the omega-3 fats supplied by cold water fish and the magnesium and vitamin E provided by whole grains. One caution: wheat may need to be avoided as it is a common food allergen associated with asthma.

Protection against Alzheimer's and Age-related Cognitive Decline

Can eating fish high in the omega-3 fatty acids, DHA(docosahexaenoic acid) and EPA (eicosapentaenoic acid), help lessen the cognitive decline and Alzheimer's disease growing in our aging population? A number of studies indicate the answer to this question is a resounding "Yes."

A report from the Framingham Heart Study published in the Archives of Neurology showed that persons whose blood levels of DHA placed them in the top quartile of values had a significantly (47%) lower risk of developing all-cause dementia than did those in the bottom quartile. Plus, greater protection against cognitive decline was obtained from consuming 2.9 than 1.3 fish meals per week. (Schaefer EJ, Bongard V, et al.).

Now, two additional positive studies have been published in the American Journal of Clinical Nutrition:

In the Zutphen Elderly Study, which involved 210 men aged 70-89 years (van Gelder BM, Tijhuis M, et al.), a linear relation was found between the estimated intake of DHA and EPA and prevention of cognitive decline.

A DHA+EPA intake of approximately 380 mg per day seemed to prevent cognitive decline. This amount of DHA+EPA would be found in just 20 grams (just 2/3 of one ounce) of Chinook salmon or in 100 grams (about 3 ounces) of cod.

Eating just two to three meals of fish a week would supply approximately 380 mg EPA+DHA per day.

In the Minneapolis study (Beydoun MA, Kaufman JS et al.) of 2251 men and women, risk of cognitive decline increased as levels of omega-6 (arachidonic acid) increased in subjects' cholesterol and other blood lipids, but decreased as the concentration of omega-3 fat (linoleic acid) increased in their blood fats.

Among subjects with high blood pressure and high cholesterol, cognitive decline was clearly associated with lower blood levels of omega-3 fats (DHA+EPA).

In all of these studies, fish consumption and the resulting increase in blood levels of omega-3 fatty acids significantly lessened mental decline over time.

How? A number of mechanisms have been suggested in recent studies to explain fish's protective effects against cognitive decline and Alzheimer's:

EPA's anti-clotting and anti-inflammatory actions promote a healthy blood supply to the brain and lower inflammation.

Since EPA and arachidonic acid are metabolized by the same enzymes, an increase in levels of EPA helps lessen the production of the pro-inflammatory compounds derived from arachidonic acid. (Arachidonic acid is a precursor of proinflammatory cytokines eicosanoids that are thought to be associated with greater cognitive decline.)

Increasing consumption of DHA may correct the DHA deficiency in the cerebral cortex characteristically seen in patients with Alzheimer disease.

DHA is involved in the membrane of ion channels in the brain, making it easier for them to change shape and transmit electrical signals.

DHA is the source of an anti-inflammatory compound made in the brain called NPD1 that lessens amyloid-beta production in cytokine-stressed human brain cells.

DHA slows the accumulation of tau, a protein involved in the development of neurofibrillary tangles, and also decreases beta amyloid formation by reducing levels of presenilin, the enzyme that separates beta amyloid from its parent protein. (Neurofibrillary tangles and beta amyloid plaques are the two types of brain lesions seen in Alzheimer's disease.)

Frank LaFerla, co-author of research published in the Journal of Neuroscience showing that DHA helps prevent the formation of neurofibrillary tangles and decreases beta amyloid formation, commented: "We are greatly excited by these results, which show us that simple changes in diet can positively alter the way the brain works and lead to protection from Alzheimer's disease pathology." Practical Tip: To keep your cognitive edge, cut back on sources of omega-6 fats, such as beef, and corn, palm, peanut, safflower and sunflower oils, and enjoy omega-3-rich cold water fish, such as scallops, at least 3 times each week.

Omega-3 Fat, DHA, Destroys Alzheimer's Plaques

DHA boosts production of the protein LR11, which destroys the beta-amyloid plaques associated with Alzheimer's disease, shows brain cell research.

"Because reduced LR11 is known to increase beta-amyloid production and may be a significant genetic cause of late-onset Alzheimer's disease (LOAD), our results indicate that DHA increases in LR11 levels may play an important role in preventing LOAD," wrote the researchers in the Journal of Neuroscience.

"Genetic polymorphisms that reduce LR11 expression are associated with increased AD risk," explained the researchers. "However these polymorphisms account for only a fraction of cases with LR11 deficits, suggesting involvement of environmental factors."

The new research investigated if fish oil and DHA could boost LR11 levels, since having high levels of LR11 have been reported to prevent plaque formation, while low levels in patients are believed to be a factor in causing the disease.

Even low doses of DHA increased the levels of LR11 in rat brain cells. Dietary DHA increased LR11 levels in the brains of rats or older mice genetically engineered to develop Alzheimer's disease. The positive effects of DHA on LR11 levels and the protection against Alzheimer's was again seen human brain cells were used. (Ma QL, Teter B, et al. J Neurosci.)

As a result of these findings, the National Institutes of Health has begun a large-scale clinical trial with DHA in patients with well established Alzheimer's disease. Lead researcher, Greg Cole, associate director of UCLA's Alzheimer Disease Research Center, thinks it may be too late for DHA to benefit these patients, but that DHA is highly likely to benefit patients in the earliest stages of Alzheimer's. And, we would add, help prevent the development of the disease in the rest of us!

DHA is the most abundant essential fatty acid in the brain, is crucial for healthy brain development, and low levels have been linked to cognitive impairment. According to the national Alzheimer's Association, approximately 5.1 million Americans suffer from Alzheimer's disease, a number that is projected to increase to 11 to 16 million sufferers by 2050.

Practical Tip: Enjoying several weekly servings of fish high in DHA, such as scallops, is a smart move.

Omega-3-Rich Diet Improves Mood, Reduces Depression

When researchers from Ohio State University evaluated blood samples taken from 43 older adults (average age 67), they found that study participants with high ratios of omega-6 to omega-3 not only had higher levels of various compounds involved in inflammation, but were more likely to suffer from depression.

Both depression and stress promote the production of pro-inflammatory cytokines. Researchers measured a number of these pro-inflammatory compounds including tumour necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and the IL-6 soluble receptor (sIL-6r). Symptoms of depression were assessed using the Center for Epidemiological Studies Depression Scale.

Levels of pro-inflammatory cytokines increased progressively as depressive symptoms increased. But when depressive symptoms were combined with high omega-6:omega-3 ratios, levels of proinflammatory cytokines skyrocketed by up to 40% more than normal—far beyond the 18% increase resulting from the presence depressive symptoms alone.

Chronic inflammation has already been linked to heart disease, type 2 diabetes, osteoporosis, cognitive decline and Alzheimer's. Earlier epidemiological (population) studies have also linked higher levels of pro-inflammatory cytokines with depressive symptoms. This new study suggests that a diet that is rich in omega-6 fats but includes few of the foods rich in omega-3 fats—such as the standard American diet—promotes not only inflammation, but depression.

The positive take-away is that increasing consumption of foods rich in omega-3s, while decreasing consumption of omega-6-rich foods, can provide some protection against depression, particularly as depressive symptoms increase.

Omega-3s are found in cold water fish, nuts, such as walnuts, and flaxseeds. Alpha-linolenic acid (ALA), the omega-3 in nuts and seeds, can be converted—albeit inefficiently—in the body to the omega-3s found in fish, eicosapentaenoic acid (EPA) and docosahexaenioc acid (DHA).

EPA improves blood flow and is also suggested to affect hormones and the immune system, both of which have a direct effect on brain function. DHA is active in the membrane of ion channels in the brain, making it easier for them to change shape and transmit electrical signals, and is involved in serotonin metabolism (reduced serotonin production and/or activity is a key factor in depression). Practical Tip: Be of good cheer. Cut back on sources of omega-6 fats, such as beef, and corn, palm, peanut, safflower and sunflower oils. Enjoy a handful of omega-3-rich walnuts and/or flaxseeds daily, and a serving of cold water fish, such as scallops, at least 3 times each week.

Description

Scallops are mollusks that have two beautiful convexly ridged, or scalloped, shells. Their two-part shell is why scallops are viewed by marine scientists as bi-valve mollusks. The part of the scallop that is generally consumed is the nut, the white muscle that opens and closes the two shells. It has a soft, fleshy texture and a delicate flavor that may be mild or briny depending upon the variety. The coral, the reproductive glands, are also edible, although they are not widely consumed in North America.

In the United States, the most widely available types of scallops include the Atlantic deep-sea scallop and the bay scallop. The flesh of the sea scallop is large, usually about one-and-a-half inches in diameter, while the bay scallop is tiny, averaging about one-half of an inch in diameter. In Europe, the most popular type is the great scallop, more commonly called Coquille St Jacques. Several hundred different species of scallops are found worldwide, in shallow areas of most seas. The Latin name of the common bay scallop is Agropecten irradians.

History

People have been enjoying scallops as a food ever since this beautiful mollusk appeared in the Earth's waters, basically since time immemorial.

The great scallop gained great prestige during the medieval era. Pilgrims visiting the shrine of St. James in Spain began to use empty scallop shells for both eating and begging. The scallop and its shell quickly became a symbol of this magnificent shrine with people using them to decorate their doorways as well as their coats of arms. In honor of the shrine, they were called the shell of St. James, now best known by their translated French name of Coquille St. Jacques.

Scallops are found in many waters throughout the world. The great scallop is abundant in the Mediterranean, while the sea and bay scallop are found concentrated in the Atlantic Ocean off North America.

How to Select and Store

Just as with any seafood, it is best to purchase scallops from a store that has a good reputation for having a fresh supply of fish. Get to know a fishmonger (person who sells the fish) at the store so that you can have a trusted resource from whom you can purchase your seafood.

Since scallops are extremely perishable, they are usually shelled, washed and frozen, or packed in ice, as soon as they are caught.

Fresh scallops should have flesh that is white and firm and have no evidence of browning. Frozen scallops should be solid and shiny, and the inside of their packaging should be free of frost. If you are planning on freezing the scallops, make sure to ask the fishmonger whether they are fresh or defrosted (if it is not clearly marked) since you will need to cook previously frozen scallops before refreezing.

Smell is a good indicator of freshness with fresh scallops being either odorless or having a slightly sweet scent. Since a slightly "off" smell cannot be detected through plastic, if you have the option, purchase displayed scallops as opposed to those that are prepackaged. Once the fishmonger wraps and hands you the scallops that you have selected, smell them through the paper wrapping and return them if they do not smell right.

When storing all types of seafood, including scallops, it is important to keep it cold since seafood is very sensitive to temperature. Therefore, after purchasing scallops or other seafood, make sure to return it to a refrigerator as soon as possible. If the scallops are going to accompany you during a day full of errands, keep a cooler in the car where you can place the scallops to make sure they stay cold and do not spoil.

The temperature of most refrigerators is slightly warmer than ideal for storing seafood. Therefore, to ensure maximum freshness and quality, it is important to use special storage methods so as to create the optimal temperature for holding the scallops. One of the easiest ways to do this is to place the scallops, which have been well wrapped, in a baking dish filled with ice. The baking dish and scallops should then be placed on the bottom shelf of the refrigerator, which is its coolest area. Replenish the ice one or two times per day. Scallops can be refrigerated for up to two days, although they should be purchased as close to being served as possible.

You can extend the shelf life of scallops by freezing them. To do so, wrap them well in plastic and place them in the coldest part of the freezer where they will keep for about three months. To defrost frozen scallops, place them in milk (or water) that has been boiled and removed from the heat. Alternatively, they can be placed in the refrigerator to defrost.