Q. You recommend eating fish twice a week. However, I’ve read that fish contain toxins and microplastics. Is it really safe to eat fish?

A. Most options in life contain both benefits and risks. Foods are no exception. Eating fish has potential benefits (largely from the omega-3 fats they contain) and risks (from the toxins). Do the benefits exceed the risks? That question has been addressed by research — much of it by colleagues here at Harvard. The answers are different for different people, and for different types of fish.

The bottom line: Fish is an important part of a healthy diet because the benefits outweigh the risks. Studies involving hundreds of thousands of people over decades have found that people who eat one or two 3-ounce servings of fish a week have a nearly 40% reduction in death from heart disease — the No. 1 cause of death in the United States and other developed nations. Regular fish intake also is associated with a lower risk of strokes and Alzheimer’s disease. These benefits make sense: regular meals of fish reduce the risks of high blood pressure, inflammation, and lethal, abnormal heart rhythms.

Fish do contain low levels of toxins, particularly mercury, polychlorinated biphenyls (PCBs), and pesticides. There’s clear evidence that mercury can adversely affect the brain of a developing baby or a young child. However, several expert panels have said there’s insufficient evidence of harm in adults to avoid eating fish, given the documented benefits.

There’s even less evidence of adverse health effects in adults from the levels of PCBs and pesticides found in fish. To put numbers on the benefits and risks, two colleagues examined many research studies and estimated that if 100,000 people ate farmed salmon twice a week for 70 years, the PCBs might cause 24 extra deaths from cancer, but the omega-3 fats would prevent 7,000 deaths from heart disease! I’ll take that trade-off any day.

You ask about the low levels of microplastics in fish. We know little about whether they pose a risk. That question is being actively studied.

What about pregnant women and young children? The mercury in fish could harm brain development in the children. However, the omega-3s in fish definitely benefit a child’s brain development. The best advice for women who are or may become pregnant, and for young children, is to avoid the fish most likely to contain higher levels of mercury (shark, swordfish, king mackerel, and tilefish) — while at the same time having at least two meals a week of other fish (canned light tuna is better than “white” albacore tuna).

The American Heart Association and other expert panels recommend that everyone eat fish at least twice a week. That’s what I do.

— by Anthony L. Komaroff, M.D.
Editor in Chief, Harvard Health Letter

Image: © gbh007/Getty Images

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