Omega-3s, Fish, and Mercury in the Diet

Salmon with citrus and vegetables
Davide Illini/Stocksy United

You've heard you should eat more fish because it's good for your heart. But you may also be concerned about mercury and other contaminants. What is a health-conscious consumer to do? Here's the low-down on fish: how much to eat, how to avoid mercury and other toxins and whether you should take a fish oil supplement.

Fish for Heart Health

Oily or "fatty" fish such as salmon, tuna, mackerel, and sardines are an excellent source of heart-healthy omega-3 fatty acids. Research suggests omega-3s may reduce inflammation, slow plaque buildup in the arteries, and reduce the risk of cardiac events in people with heart disease.

Is an Omega-3 Supplement as Good as Fish?

Omega-3s are a unique form of nutrient known as "essential," meaning that you must obtain them from food or a supplement pill. Your body cannot make the nutrient from other fats, carbohydrates, or proteins. Omega-3s are not very common in the foods we eat and are mostly found in fish and seafood.

If you don't enjoy fish, you can opt for a supplement. While it's generally best to get nutrients from food, it's better to get fish oil in your diet than not. If that means taking a supplement, go for it (but consult your doctor first). Current research indicates that they are as good for you as food sources.

How Much Omega-3 Do You Need?

The American Heart Association recommends eating fish twice a week. If you're taking a supplement or getting omega-3s through fortified foods, then shoot for 500 mg a day—the equivalent of two servings of oily fish a week. Consult your doctor before starting this or any other supplement. Some medications, such as beta-blockers, blood thinners, and diuretics could interact with fish oil.

Beyond fish and fish oil, there are plant-based forms of omega-3s. For example, a handful of walnuts, a tablespoon of canola oil over salad or a tablespoon of ground flaxseed over your breakfast cereal are all good ways to get omega-3s in your diet.

Mercury in Fish

Mercury is a naturally occurring element, but it is also a byproduct of pollution. In high amounts, ingesting mercury can cause neurological problems. All fish and seafood contain some amount of mercury. So while it is impossible to avoid mercury entirely when eating fish and seafood, you can make lower-mercury choices. Experts recommend avoiding the fish with the highest levels of mercury (especially if you're a woman who's pregnant, nursing or who could become pregnant or a child), and eating lower-mercury fish and seafood.

Low-Mercury Fish High-Mercury Fish
Shrimp, canned light tuna, salmon, and pollock King mackerel, shark, swordfish, and tilefish
Sardines and anchovies Albacore tuna has more mercury than light tuna.

As with other animal foods, seafood can also have additional contaminants: dioxins and polychlorinated biphenyls (PCBs), although nutrition researchers agree that the benefit of eating fish and seafood far outweighs any potential risk of PCBs you may consume.

Eating Fish During Pregnancy

The EPA and FDA put out a report in 2014 recommending that these three groups of people should eat more low-mercury fish: pregnant and breastfeeding women, women who might become pregnant, young children. They found that pregnant women were not eating enough fish and therefore not getting enough of the omega-3s that are so important to fetal brain development. The EPA-FDA report recommends pregnant women eat between 8 - 12 ounces of low-mercury fish each week.

Wild vs. Farmed Salmon

There is considerable controversy about wild versus farmed fish, especially salmon. Wild fish advocates state that wild fish, such as wild Atlantic salmon, have fewer PCB contaminates than their farmed counterparts. Proponents of farmed fish, especially farmed Pacific salmon, note that farmed fish have as much and sometimes more DHA and EPA omega-3s than wild salmon.

As a consumer, it is important to know that even these claims may change as farmed and wild fish purveyors change their methods of feeding and collection to meet consumer demand. Ultimately, the benefits of both farmed and wild fish outweigh the risks when it comes to protecting your health.

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Article Sources

  • EPA-FDA Advisory on Mercury in Fish and Shellfish
  • Harris, W., et al. Comparison of the effects of fish and fish-oil capsules on the n3 fatty acid content of blood cells and plasma phospholipids. American Journal of Clinical Nutrition, Vol. 86, No. 6, 1621-1625, December 2007.
  • Massaro M., et al. Omega-3 fatty acids, inflammation, and angiogenesis: basic mechanisms behind the cardioprotective effects of fish and fish oils. Cell Mol Biol. 2010 Feb 25;56(1):59-82.
  • Mozaffarian, D. et al. Fish Intake, Contaminates, and Human Health: Evaluating the Risks and Benefits JAMA. 2006;296(15):1885-1899.
  • Sacks, F. "Ask the Expert" Harvard School of Public Health. 
  • Scientific Report of the 2015 Dietary Guidelines Advisory Committee, Appendix E-2.38.
  • What You Need to Know About Mercury in Fish and Shellfish. Environmental Protection Agency. EPA Factsheet.