Fish is rich in the long-chain polyunsaturated omega-3 fatty acids, eicosapentanoic acid (EPA) and docosahexonoic acid (DHA) and has a higher proportion of total fatty acids coming from polyunsaturated and monounsaturated fatty acids than from saturated fatty acids. The American Heart Association recommends eating one serving (3.5 oz. cooked, or about ¾ cup of flaked fish) of a variety of fish at least twice a week, especially fish containing high levels of the omega-3 fatty acids that are considered to be of benefit cardiovascular health. Research has shown that omega-3 fatty acids decrease risk of abnormal heartbeats (arrhythmias), which can cause sudden death, decrease triglyceride levels, and slow the accumulation of atherosclerotic plaque. A meta-analysis of 19 different studies found that consumption of fish was associated with about a 20% decrease in unstable angina and heart attack among those who ate fish 4 times per week, the highest category of fish consumption. In a dose-response analysis, each additional 100 gm. serving of fish per week was associated with a 5% reduced risk.
Recommendations vary according to the omega-3 content of fish according to their species and whether they are farmed or not. Fatty fish like salmon, mackerel, herring, lake trout, sardines and albacore tuna are high in omega-3 fatty acids. Other fish are lower in omega-3 content, for example tilapia has about 0.2 grams of omega-3s per serving compared to wild or farmed salmon with more than 1.5 grams. Some farmed fish, when fed on a cornmeal and soymeal based diet, are lower in omega-3 fatty acids than wild caught fish that feed on omega-3 rich algae and other aquatic plants.
As can be seen from the table below, the recommended weekly amount of omega-3 fatty acids can be consumed
with a single meal of fish high in omega-3 fatty acids, or multiple meals of species with lesser amounts.
One 6-oz serving per week of Two 6-oz servings per week of Three 6-oz servings per week of:
wild-caught, or canned)
whitefish/walleye Atlantic mackerel
trout (wild-caught) Flatfish
Source: Nutrition Journal, March 15, 2013, 12:33.
Fish is not risk free. Some types of fish may contain high levels of mercury, mostly in the form of methylmercury, PCBs (polychlorinated biphenyls), dioxins and other environmental contaminants. Levels of these substances are generally highest in animals at the top of the food chain that are older, larger, and in predatory fish and marine mammals. Mercury is of concern, especially among children and pregnant women because of the potential for adverse effects on fetal and child neurodevelopment and adult cardiovascular disease.
According to the American Heart Association, the benefits and risks of eating fish vary depending on a person's stage of life.
• Children and pregnant women are advised by the U.S. Food and Drug Administration (FDA) to avoid eating those fish with the potential for the highest level of mercury contamination (e.g., shark, swordfish, king mackerel or tilefish); to eat up to 12 ounces (two average meals) per week of a variety of fish and shellfish that are lower in mercury (e.g., canned light tuna, salmon, pollock, catfish); and check local advisories about the safety of fish caught by family and friends in local lakes, rivers and coastal areas.
• For middle-aged and older men and postmenopausal women, the benefits of fish consumption far outweigh the potential risks when the amount of fish are eaten is within the recommendations established by the FDA and Environmental Protection Agency.
• Eating a variety of fish will help minimize any potentially adverse effects due to environmental pollutants.
The FDA and Environmental Protection Agency periodically update advice on fish consumption for young children, women who might become pregnant, pregnant women and breastfeeding women. Their guidelines should be referred to for the most up to date advice on consumption of seafood. In general they call for eating fish with high levels of DHA and EPA but also that are low in mercury and other contaminants.
Because of the popularity of tuna there has been considerable discussion of the advisability of pregnant women eating it. Some authorities consider up to 6 ounces or even 12 ounces a week of canned light tuna to be beneficial (canned albacore tuna has about double the mercury as canned light tuna), others recommend substituting shrimp, scallops, sardines, salmon, oysters and tilapia because they are the lowest-mercury seafoods. It should be noted that about 90% of U.S. bought shrimp is imported and it may carry risk of other contaminants including antibiotic residues. Avoid eating shark, swordfish, king Mackerel, or tilefish because they contain high levels of mercury. Consumer Reports also recommends limiting consumption of grouper, Chilean sea bass, bluefish, halibut, black cod, Spanish mackerel and fresh tuna.
As an increasingly large share of fish is farm-raised fish it should be noted that aquaculture feeds fish with an unnatural diet that may include high levels of pesticides, antibiotics and other toxins. An increasing share of fish sold in the U.S. is farmed and much of the farmed fish is imported. Fish farmed in Canada and European Countries have a better safety record than those from Asian and Latin American countries that have less rigorous standards for avoidance of contamination with drugs, pesticides, heavy metals such as mercury and other contaminants and minimizing the environmental impact of their farming methods. 
Because mercury is a known neurotoxin, there has been concern that, although consumption of high-fat fish and fish oils have been shown to provide benefits for cognitive development and preservation, high levels of seafood consumption might lead to accumulation of mercury and be related to development of Alzheimer disease and dementia. A careful autopsy study found that moderate seafood consumption of at least one meal a week is positively correlated with higher brain mercury levels but there was no correlation with increased levels of Alzheimer disease or dementia. The Scientific Report of the 2015 Dietary Guidelines Advisory Committee concluded that with regard to contaminants, for the majority of wild caught and farmed species of fish, neither the risks of mercury nor organic pollutants outweigh the health benefits of seafood consumption.
Fish vs. Plant-Based Food
If omega-3 fatty acids are the main benefit, or at least a known benefit of eating seafood, is eating fish important as a source or are plant based food sources equally good? Foods such as flaxseeds, walnuts, soybeans and canola oil are rich in a different omaega-3 fatty acid, linolenic acid that the body converts to EPA and DHA. There is some evidence that women on vegan diets have high omega-3 levels based on conversion of shorter-chain fatty acids into omega-3 long-chain fatty acids. There is also evidence that fish oil supplements are no better than a placebo with regard to prevention of cardiovascular diseases. In a large general-practice cohort of patients with multiple cardiovascular risk factors, daily treatment with n−3 fatty acids did not reduce cardiovascular mortality and morbidity. There are a variety of guides to assist consumers in buying seafood that is both healthy and responsibly farmed or wild caught. The Environmental Defense Fund (EDF) has a Seafood Selector that is available at http://seafood.edf.org/guide/best. It groups fish according to eco-friendliness and levels of mercury: best choices, OK choices and worst choices.
The Monterey Bay Seafood Watch Recommendations
The Monterey Bay Seafood Watch website at https://www.seafoodwatch.org provides U.S. state specific guides to sustainable seafood. Seafood Watch recommendations are grouped in the following categories:
1) Best Choices. Buy first, they're well managed and caught or farmed in ways that cause little harm to habitats or other wildlife. A few examples of fish to buy first from the 2016 West Coast guide are: Catfish (US), Clams, Mussels & Oysters, Cod: Pacific (AK), Crab: King, Snow & Tanner (AK) Lingcod, (Canada troll & US longline, troll) Lionfish (US), Lobster: Spiny (Mexico), Prawn: Freshwater (Canada & US) Prawn: Spot (AK & Canada), Rockfish (AK, CA, OR & WA), Sablefish (Canada farmed & AK), Salmon (AK & New Zealand).
2) Good Alternatives. Buy, but be aware there are concerns with how they're caught or farmed. A few examples of good alternatives from the 2016 West Coast guide are: Cod: Pacific (Canada & US), Crab: Dungeness (Canada & US) Lingcod (Canada), Lobster (Bahamas & US), Mahi Mahi (US troll & Ecuador) Octopus (Portugal & Spain pot, trap), Salmon (Canada, CA, OR & WA wild) Scallops: Sea (wild).
3) Avoid. Take a pass on these for now, they're overfished or caught or farmed in ways that harm other marine life or the environment. A few examples of fish to avoid from the2016 West Coast guide are: Sharks, Shrimp (imported, if not listed), Squid (China, India & Thailand), Swordfish (imported longline), Tuna: Albacore (except US troll, pole and line, and longline),Tuna: Bluefin.
So the bottom line is that eating fish and other seafoods can be healthy, but making choices that are safe and ecologically responsible requires careful selection. It can also be noted that it may be just as beneficial to health to substitute plant-based foods, vegetables, fruit, beans and nuts for red meat and processed meats as it is to substitute seafood. Furthermore, there is just not enough wild or farmed seafood for all 7.4 billion of us to eat seafood twice a week.
Endnotes and Links
Bell GA, Kantor ED, Lampe JW, Kristal AR, Heckbert SR, White E. Intake of long-chain ω-3 fatty acids from diet and supplements in relation to mortality. Am J Epidemiol. 2014;179(6):710-720.
Leung SSL, Yinko, RD, Stark KD, Thanassoulis G, Pilote L. Fish Consumption and Acute Coronary Syndrome: A Meta-Analysis. The American Journal of Medicine (2014) 127, 848-857.
 Oken E, Guthrie LB, Bloomingdale A, et al. A pilot randomized controlled trial to promote healthful fish consumption during pregnancy: The Food for Thought Study. Nutrition Journal201312:33 DOI: 10.1186/1475-2891-12-33.
Budtz-Jorgensen E, Grandjean P, Weihe P: Separation of risks and benefits of seafood intake. Environ Health Perspect 2007, 115(3):323–327.
American Heart Association. http://www.heart.org/HEARTORG/HealthyLiving/HealthyEating/Nutrition/The-American-Heart-Associations-Diet-and-Lifestyle-Recommendations_UCM_305855_Article.jsp#.WFWzo7GtpaM
 EPA-FDA Advisory on Mercury in Fish and Shellfish. https://www.epa.gov/fish-tech/epa-fda-advisory-mercury-fish-and-shellfish
 American Heart Association. http://www.heart.org/HEARTORG/HealthyLiving/HealthyEating/Nutrition/The-American-Heart-Associations-Diet-and-Lifestyle-Recommendations_UCM_305855_Article.jsp#.WFWzo7GtpaM
 Parker-Pope T, The Tuna Debate Still Swirls. New York Times, March 3, 2015.
 Report of the Joint Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO) Expert Consultation on the Risks and Benefits of Fish Consumption, 2011. Available at http://www.fao.org/docrep/014/ba0136e/ba0136e00.pdf
A tilapia tell-all. University of California Berkeley Wellness Letter Vol 31, Issue 8, April 2015.
Scientific Report of the 2015 Dietary Guidelines Advisory Committee. Advisory Report to the Secretary of Health and Human Services and the Secretary of Agriculture.
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