November 2008 Issue

Holy Mackerel! Go Fish for an Ocean of Omega-3 Benefits
By Diane Welland, MS, RD
Today’s Dietitian
Vol. 10 No. 11 P. 28

Americans should learn to like the lean (such as tilapia) and love the fat (fatty varieties such as salmon) to best boost their EPA/DHA intake.

When a recent Journal of the American Dietetic Association article reported that “all other nutritional content aside, the inflammatory potential of hamburger and pork bacon is lower than the average serving of farmed tilapia,” the media were quick to jump on it.1 Headlines across the country declared tilapia worse than bacon, and almost overnight this favored fish became “potentially dangerous,” “harmful,” and “unhealthy.” The flurry of attention over a seemingly “good food gone bad” raised a number of questions about seafood, leaving some dietitians as confused as consumers.
The reality is that fish (tilapia included), if properly prepared, is a highly nutritious food that is low in saturated fat, high in high-quality protein, and rich in nutrients touted for their health benefits.2 But while all seafood can and should be part of a healthful diet, not all fish contain the same kinds and amounts of beneficial compounds.

So, what do we really need to know about seafood, and what should we tell our clients about tilapia, catfish, shellfish, and fish in general?

Zero in on Omega-3s
Like all seafood, tilapia contains long-chain polyunsaturated omega-3 fatty acids called eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), nutrients found almost exclusively in fish.3 Some fish, however, have more than others. The fattiest fish tend to be cold-water varieties such as salmon, rainbow trout, mackerel, sardines, and anchovies, while the leanest fish tend to be catfish, tilapia, cod, pollock, shrimp, crabs, and clams.2,4

EPA and DHA have been touted for their heart-health benefits since the late 1970s, when epidemiological studies discovered low cardiovascular mortality among Eskimos who consumed a lot of fatty fish.5 Observational studies in Japan, another fish-eating culture, noted this same phenomenon, reporting heart disease deaths at rates of about one half of Western countries.6

Ironically, these findings held true in spite of other high risk factors. Several studies by Akira Sekikawa, MD, MPH, PhD, of the University of Pittsburgh found that Japanese men had significantly less cholesterol buildup in their arteries compared with white men living in the United States, despite similar blood cholesterol and blood pressure readings, similar rates of diabetes, and much higher rates of cigarette smoking.7 Furthermore, since Japanese immigrants who came to America and switched to a Western diet suffered atherosclerosis similar to U.S. natives, genetic differences were ruled out.8
Could it be the fish they eat? Researchers think so. A 2004 meta-analysis of 13 cohort studies found that eating fish as little as once per week reduced the risk of dying from coronary heart disease by 15%. And the more fish consumed, the lower the risk (add an extra 5-ounce fish dinner per week, and the risk of dying will drop another 7%).9

This year, another review of cohort and randomized clinical trials found that people who took in as little as 250 milligrams of EPA/DHA per day (an amount equivalent to eating about 4 ounces of fatty fish per week) reduced cardiovascular death risk by 36% compared with those who consumed no fish at all.10
When it comes to fish intake, Americans are no match for the Japanese, who eat an average of 3 ounces of fish every day and a whopping 21 ounces of fish per week. Even Americans who regularly eat fish twice per week take in less than one half that amount.7

The more fish eaten, the more omega-3 fatty acids consumed. The Japanese wolf down about 1 gram of omega-3 fatty acids per day—that’s five times more than the average American.7 Since our bodies cannot produce omega-3 fatty acids, blood levels directly reflect intake.

In a study published in August in the Journal of the American College of Cardiology, Sekikawa measured omega-3 fatty acid blood levels in 868 middle-aged men from Japan and the United States. Compared with the U.S. subjects, who were both Japanese-American and white men, Japanese omega-3 blood levels were twofold higher, which many scientists believe is directly linked to low incidence of heart disease.

“Omega-3 fatty acids levels in the blood have a greater impact on risk for heart disease than cholesterol, total fat, or fiber,” says William S. Harris, PhD, director of the University of South Dakota Nutrition and Metabolic Disease Research Institute. “The higher the omega-3 levels, the lower the risk of heart disease and death and vice versa.”

Harris cites a randomized clinical trial conducted in Italy and recently published in The Lancet that specifically targeted omega-3 fatty acids and chronic heart failure.11 “In this study, people who had chronic heart failure and were given omega-3 fatty acids were 9% less likely to die than those who didn’t take omega-3 fatty acids.” This study used prescription omega-3 capsules.13

Preventing cardiovascular disease, however, isn’t the only omega-3 benefit. There is ample evidence that these fats are essential for optimal brain development during pregnancy and in infancy.12 “Data show that women who eat seafood when they are pregnant and lactating have children with better cognitive function than children whose mothers did not eat seafood,” says Penny M. Kris-Etherton, PhD, RD, of Penn State University. “These children also score higher on IQ tests.”

How Much Is Enough?
Both the American Heart Association (AHA) and the American Diabetes Association recommend that Americans eat at least two servings of fatty fish per week, totaling about 8 ounces of seafood and providing about 500 milligrams per day of EPA/DHA.13 The 2005 Dietary Guidelines for Americans echo this advice. The AHA aims even higher for those with cardiovascular risk, encouraging an intake of 1 gram of EPA/DHA per day by adding either one or two servings of seafood to a weekly meal plan or by taking supplements.
Considering the U.S. population’s current consumption hardly reaches 100 milligrams per day of EPA/DHA, this is a tall order. Add to this the “all-or-nothing” principle, which means only a small percentage of the population actually eats fish on a regular basis but their intake is high, and dietitians have their work cut out for them.13 Still, it is a goal well worth striving to reach, not only because mountains of evidence show omega-3s fight heart disease and maximize brain development in newborns, but also because plenty of promising research suggests omega-3 fatty acids can help control Alzheimer’s disease and dementia, eye disease, and even depression, violence, and aggression.
Boost Brain and Eye Power
Although DHA is found throughout the body, the most concentrated source is the brain, which is composed of nearly 60% polyunsaturated fats.14 From research, we know that DHA levels in the brain decrease as we age. We also know that people with Alzheimer’s disease have low levels of DHA in their brain. Eating seafood can replace those losses, reducing risk of Alzheimer’s disease and dementia and protecting the brain from natural aging. In some cases, it can even slow the progression of these two debilitating diseases.15,16

The Framingham Heart Study tracked nearly 900 healthy men and women (average age of 76) for a mean of nine years. Researchers found that those adults who ate three servings of fish per week lowered their risk of developing dementia (from all causes) by 47% and their risk of developing Alzheimer’s disease by 39% compared with those people who ate little or no fish.17

Another 2008 study from the American Academy of Neurology showed that eating baked or broiled fish such as tuna three or more times per week protected against memory loss and stroke, slashing risk by more than one quarter in more than 2,300 people aged 65 or older. However, these results did not appear in people who regularly ate fried fish, implying that how the fish is prepared is just as important as the amount consumed.

To test the data on DHA and Alzheimer’s disease, the National Institutes of Health is undertaking an 18-month large-scale clinical trial, scheduled to conclude this month. The trial, which involves 400 participants older than the age of 50 with mild to moderate Alzheimer’s disease, will evaluate whether DHA slows functional decline.5

Like the brain, the retina also contains abundant DHA, which makes up as much as 50% of the retina cells.14,18 Here its action is twofold: first as a vital component of the photoreceptor cells, called rods and cones, and second as part of the line of defense that protects the pigment cells from damage and destruction. This explains why people who ate fish more than once per week had significantly lower rates of age-related macular degeneration in several population studies.18 The newest study from the London School of Hygiene & Tropical Medicine found that people who regularly ate oily fish once per week were one half as likely to develop age-related macular degeneration than those who didn’t eat fish.

Other research has hinted that omega-3 fatty acids from fatty fish consumption may keep people safe from certain types of cancer, especially breast, prostate, colon, and renal. Although data in this arena are scarce, it may be a promising area for future research.19   

Manage Mental Illness
Perhaps the most intriguing research on omega-3 fatty acids focuses on the role of nutrition in psychiatric disorders. Since DHA and EPA are essential components of the nervous system, some scientists believe they may alter neurochemical pathways in the brain that affect behavior and mental health, paving the way for nutrition to be part of a treatment plan for mental illness and antisocial behavior. Although research in this controversial area is primarily epidemiological, several clinical trials in England, the United States, and Denmark have shown that nutrition, and specifically omega-3 fatty acids, can make a difference.14,20

“We have very strong data that adding omega-3 fatty acids (in the form of fish or supplements) decreases aggression, impulsivity, and depression in adults,” says Joe Hibbeln, MD, senior clinical investigator at the National Institute on Alcohol Abuse and Alcoholism of the National Institutes of Health in Bethesda, Md. “This data is even stronger for kids with mood disorders and disorderly conduct issues, like some types of ADHD [attention-deficit/hyperactivity disorder].”

Hibbeln looked at omega-3 fatty acid intakes in 38 countries, comparing them to more than a dozen different outcomes—from cardiovascular disease and stroke to postpartum depression and homicide. In all cases, higher intakes of omega-3 fatty acids and seafood were directly correlated with positive outcomes, while lower levels showed the opposite.21

Hibbeln believes much of the chronic degenerative disease and mental illness afflicting people in the United States is a result of an omega-3 deficiency. Exactly how to define a deficiency remains in question, but like other scientists, Hibbeln considers the Japanese diet the gold standard and recommends Americans follow AHA guidelines at the very least.
“We can solve a lot of the world’s problems if people just [eat] more seafood,” he notes.
Too Much of a Good Thing?
Although the scientific and nutrition communities adamantly encourage Americans to eat more fish and shellfish on a regular basis, many consumers worry about getting too much of a good thing.  Reports of people getting sick from contaminants in fish are few and far between, and overconsumption of seafood and exposure to high levels of contaminants aren’t likely to be issues, particularly since according to a review of National Health and Nutrition Examination Survey data by Tufts University researchers, on any given day only one quarter of the population reported consuming any DHA and EPA from fish.22

“For the general population, the benefits of eating fatty fish far outweigh any risk,” says Dariush Mozaffarian, MD, DrPH, a Harvard professor and coauthor of a study titled “Fish Intake, Contaminants, and Human Health.” “Only a few commercial fish species have high levels of mercury, PCBs [polychlorinated biphenyls], and dioxins, and these are not typically eaten by consumers. Plus, in the general population, the health effects from the small amounts of contaminants related to eating fish are not well established. Women of childbearing age should follow the EPA/FDA advisory.”

In 2004, Health and Human Services advised pregnant women, nursing mothers, young children, and women who may become pregnant to avoid shark, swordfish, king mackerel, and tilefish due to high levels of mercury. They also recommended this population curb intake to no more than 12 ounces of fish or shellfish per week.

Mozaffarian says commercial ocean-caught fish generally have very low levels of PCBs and dioxins. Higher levels, he contends, are usually found in locally caught freshwater fish from lakes or inland rivers. That’s why it’s important for people who regularly eat sports-caught fish from family and friends to check local water and fish advisories.
For the majority of people who consume commercial fish, eating a variety of seafood, especially oily or dark meat species with higher levels of omega-3s, one or two times per week is enough. Not only will this protect you from potential contaminants, but it also will ensure you get adequate levels of this healthy fat. “Omega-3 levels naturally vary among fish species,” says Mozaffarian. “Depending on if you’re eating pollock or salmon, this could translate into a tenfold difference.”

What About Omega-6s?
The biggest controversy surrounding seafood centers around the polyunsaturated omega-6 fatty acid linoleic acid, predominantly found in soybean oil. In one camp are scientists such as Harris who contend that linoleic acid “is beneficial and actually promotes anti-inflammatory biomarkers that protect against cardiovascular disease,” as evidenced by human clinical data.23

On the other side are scientists such as Hibbeln, who believes that “omega-6 fatty acids lower the effectiveness of omega-3s by blocking cell absorption, which is why the omega-3 to omega-6 ratio is important. While linoleic does produce some anti-inflammatory substances, it produces more proinflammatory compounds. Linoleic does more harm than good.”14,21

However, both scientists agree that tilapia or any other lean fish or shellfish isn’t a food you should eliminate from your diet. “Tilapia may not be the best choice in seafood, especially for omega-3 fatty acids, but it’s certainly better than a hot dog and French fries and it still has some omega-3 fatty acids, and some is better than none,” says Hibbeln.

What to Tell Clients
• Make fish a priority. Encourage clients to eat seafood at least twice per week.

• Be adventurous. Experiment with different types of seafood.

• Bone up on fatty fish such as salmon and trout, which offer the most heart-health benefits. If you do enjoy lean fish such as tilapia and catfish, think about adding another serving of fatty fish to your weekly dinner menu to make up for it.

• Lean fish are good, too. Aside from being low in fat and calories, lean fish and shellfish are also loaded with micronutrients necessary for good health. For example, tilapia is high in selenium, clams are high in iron, and oysters are high in zinc (and omega-3s).
• Prepare it properly. Teach clients to cook fish at home using low-fat techniques such as broiling, baking, stir-frying, and sautéing. Avoid fried fish and highly processed fish foods such as fish sticks.

— Diane Welland, MS, RD, is a dietitian and a freelance food and nutrition writer based in Springfield, Va.


Farmed vs. Wild
Are farm-raised fish just as nutritious as wild-caught fish in terms of fatty acid content? “Omega-3 fatty acid composition is species specific, meaning this fat varies depending on the type of fish,” says Jennifer Wilmes, RD, from the National Fisheries Institute.
While this is true, some say there’s more to it than that. “The quality of the fat in fish directly reflects the composition of oil in the diet,” says Penny M. Kris-Etherton, PhD, RD, of Penn State University. “Salmon and trout need omega-3 fatty acids for growth and so the content of omega-3s is the same or even higher in farm-raised fish, but other fish can thrive on vegetable oil.”

In fact, many fish farmers now use vegetable oil in their feed, not only because it stimulates appetite and increases growth but also because it’s cheaper and easier to purchase than marine oil, according to a February 28 article in Science Daily.

Kris-Etherton contends that certain farmed fish such as tilapia and catfish, which are fed soybean oil, are not as healthy as they could be if they were fed marine oils such as the kind you would find in the wild. “If the goal is to increase our omega-3 fatty acid intake by eating fish,” says Kris-Etherton, “then farm-raised fish practices aren’t helping the situation. This is what we should be concerned about.”

Nutrition Chart
Fact Sheet

— DW


1. Weaver KL, Ivester P, Chilton JA, et al. The content of favorable and unfavorable polyunsaturated fatty acids found in commonly eaten fish. J Am Diet Assoc. 2008;108(7):1178-1185.

2. Institute of Medicine. Seafood Choices: Balancing Benefits and Risks (report brief). Washington, D.C.: National Academies Press; 2006. Available at:

3. Harris WS. You are what you eat applies to fish, too. J Am Diet Assoc. 2008;108(7):1131-1133.

4. Institute of Medicine. Balancing Choices: Supporting Consumer Seafood Consumption Decisions (fact sheet). Washington, D.C.: National Academies Press; 2006. Available at:

5. Studies find new omega-3 benefits: But are you getting the right healthy fats? (special report) Tufts Health & Nutrition Letter. 2007;25(5):4-5.

6. Iso H, Kobayashi M, Ishihara J, et al. Intake of fish and n3 fatty acids and risk of coronary heart disease among Japanese: The Japan Public Health Center-Based (JPHC) Study Cohort I. Circulation. 2006;113:195-202.

7. Sekikawa A, Curb DJ, Ueshima H, et al. Marine-derived n-3 fatty acids and atherosclerosis in Japanese, Japanese-American, and white men: A cross-sectional study. J Am Coll Cardiol. 2008;52:417-424.

8. Sekikawa A, Ueshima H, Kadowaki T, et al. Less subclinical atherosclerosis in Japanese men in Japan than in white men in the United States in the post-World War II birth cohort. Am J Epidemiol. 2007;165(6):617-624.

9. He K, Song Y, Daviglus ML, et al. Accumulated evidence on fish consumption and coronary heart disease mortality: A meta-analysis of cohort studies. Circulation. 2004;109(22):2705-2711.

10. Mozaffarian D. Fish and n-3 fatty acids for the prevention of fatal coronary heart disease and sudden cardiac death. Am J Clin Nutr. 2008:87(6):1991S-1996S.

11. GISSI-HF Investigators. Effect of n-3 polyunsaturated fatty acids in patients with chronic heart failure (the GISSI-HF trial): A randomised double-blind, placebo-controlled trial. Lancet. 2008;372(9645):1231-1239.

12. Hibbeln JR, Davis JM, Steer C, et al. Maternal seafood consumption in pregnancy and neurodevelopmental outcomes in childhood (ALSPAC study): An observational cohort study. Lancet. 2007;369(95610:578-585.

13. Kris-Etherton PM, Hill AM. N-3 fatty acids: Food or supplements? J Am Diet Assoc. 2008;108(7):1125-1130.

14. Report of the British Associate Parliamentary Food and Health Forum. The Links Between Diet and Behavior: The Influence of Nutrition on Mental Health. London: British Associate Parliamentary Food and Health Forum; 2008.

15. Welland D. The latest research finds vegetables, tea, fish help fend off Alzheimer’s. Environmental Nutrition. 2007;30(9):1,6.

16. Freund-Levi Y, Eriksdotter-Jönhagen M, Cederholm T, et al. Omega-3 fatty acid treatment in 174 patients with mild to moderate Alzheimer’s disease: OmegaAD study: A randomized double-blind trial. Arch Neurol. 2006;63(10):1402-1408.

17. Schaefer EJ, Bongard V, Beiser AS, et al. Plasma phosphatidylcholine docosahexaenoic acid content and risk of dementia and Alzheimer disease: The Framingham Heart Study. Arch Neurol. 2006;63(11):1545-1550.

18. Weatherby C. Omega-3s linked to eye health ... again. Vital Choices. 2008;5(230):1. Available at:,0,w

19. Berquin IM, Edwards IJ, Chen YQ. Multi-targeted therapy of cancer by omega-3 fatty acids. Cancer Lett. 2008;269(2):363-377.

20. Hibbeln JR, Ferguson TA, Blasbalg TL. Omega-3 fatty acid deficiencies in neurodevelopment, aggression and autonomic dysregulation: Opportunities for intervention. Int Rev Psychiatry. 2006;18(2):107-118.

21. Hibbeln JR, Nieminen LRG, Blasbalg TL, Riggs JA, Lands WEM. Healthy intakes of n-3 and n-6 fatty acids: Estimations considering worldwide diversity. Am J Clin Nutr. 2006;83(6):S1483-S1493.

22. Mozaffarian D, Rimm EB. Fish intake, contaminants, and human health evaluating the risks and the benefits. JAMA. 2006;296(15);1885-1899.

23. Harris WS. The omega-6/omega-3 ratio and cardiovascular disease risk: Uses and abuses. Curr Atheroscler Rep. 2006;8(6):453-459.