Ask Tufts Experts

The new federal dietary guidelines call for at least two servings of fish a week. At this time of year, the only fish available in my grocery store is farm-raised. I have also read that you should limit your consumption of farm-raised fish to two times a month. What should I do?

The new dietary guidelines don’t actually set a recommended serving amount for fish, but do note, “Evidence suggests that consuming approximately two servings of fish per week (approximately eight ounces total) may reduce the risk of mortality from coronary heart disease and that consuming EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) may reduce the risk of mortality from cardiovascular disease in people who have already experienced a cardiac event.” EPA and DHA are omega-3 fatty acids found in fish and shellfish. The American Heart Association does specifically recommend consuming fish twice a week.

The FDA has not issued any recommended limits on consumption of farm-raised fish, though there are certain FDA recommended limits, specifically for pregnant women and children, to avoid mercury in fish. Concern about farm-raised salmon arose after a study by the Environmental Working Group found polychlorinated biphenyls (PCBs), which the Environmental Protection Agency (EPA) calls “a probable human carcinogen,” in 70 percent of such fish they bought at supermarkets.

But that study tested only 10 salmon fillets. Mark Woodin, PhD, a Tufts epidemiologist, has noted that while farm-raised salmon probably does have higher levels of PCBs than wild salmon, it’s very difficult to say just how toxic they might be. The EPA’s limits on PCBs are stricter than the FDA’s, but are based on the amount of PCBs thought to be capable of causing one additional cancer case in 100,000 people over a 70-year lifetime.

You have to balance risks and benefits, advises Alice Lichtenstein, Gershoff Professor at Tufts’ Friedman School of Nutrition Science and Policy. “The risk of developing cardiovascular disease (CVD) is high; it is the leading cause of death and disability in the US, and half of women in the US will die of CVD. Other than the special issue of pregnant women and children, the risk of adverse effects from contaminants in fish is extremely low, theoretical at this point.”

If you’re still wary, try canned tuna and salmon, which usually use wild fish because it’s firmer. All year-round, many supermarkets offer high-quality frozen fish that may include wild varieties.