The guidelines for eating fish couldn't be simpler these days: Fish are an excellent source of high-quality protein and healthy omega-3 fatty acids, such as DHA, which are good for the heart and brain.
So eat plenty of fish, but no more than twice a week if you're a child, a pregnant woman or a woman hoping to get pregnant because fish can also contain industrial pollutants, which are bad for a developing brain.
But the benefits of eating fish outweigh the risks, probably, unless you're catching your own from a river with the kind of pollutants that change the sex of the fish. So stick with store-bought fish. But, oh yeah, only eat those fish harvested in a sustainable manner because we've depleted up to 95 percent of many fish species with reckless fishing techniques.
Confused? Unfortunately, so are doctors.
The one that got away
Doctors at the Harvard School of Public Health published a massive study last week in the Journal of the American Medical Association. In their rosy assessment, eating a modest amount of certain fish high in omega-3 each week, as little as three ounces of salmon, for example, reduces the risk of coronary heart disease by 36 percent. Population mortality drops by 17 percent, too. The implication is that eating fish is the single most important thing you could do for your health.
"For major health outcomes among adults, the benefits of eating fish greatly outweigh the risks," said lead author Dariush Mozaffarian in a Harvard press statement. "Somehow this evidence has been lost on the public."
Well, maybe, Dr. M., the message is lost amidst government warnings about safe levels of consumption, as if fish were poison.
Or maybe because Harvard's message was overshadowed by a report from the Institute of Medicine issued the very same day, which had a more sober assessment. That study found that there's only enough evidence to say that fish might reduce the risk of heart disease. Scientists involved said that Harvard's 36-percent figure is way too high. The Institute of Medicine also published a flowchart of who can eat what fish and when.
That one needs a flowchart to determine the safety of fish is worrisome enough, but the complexity is almost comical [You should see the flowchart!].
One fish, two fish, bad fish, good fish
Many fish have a healthy type of polyunsaturated fat, called omega-3 fatty acids. Omega-3s lower bad cholesterol in the blood and raise good cholesterol, making this a healthier choice over saturated fats found plentifully in pork, beef and dairy products.
The two fish studies differ in their assessment on whether a health benefit comes from eating more omega-3s in fish or less saturated fat elsewhere.
One type of omega-3, called DHA, seems to be beneficial for brain and eye development in infants and might ward off depression and dementia among older adults. Japan, Iceland and Singapore consume lots of fish, and this could be related to their long life-expectancy rates, the highest in the world.
Fish would be the logical healthy choice if it weren't for mercury, PCBs, dioxin and other pollutants from ocean trash dumping that can accumulate in their bodies; fish higher up the food chain—shark, swordfish, king mackerel, tuna—contain more pollutants.
Mercury in particular damages developing nervous systems, hence the warning for women of childbearing age. PCBs, which were banned in the 1970s, and dioxin are great unknowns. The Harvard study notes that the Inuit have low rates of heart disease due to high consumption of marine fat and blubber; the study does not mention that the Inuit have by far the highest blood levels of PCBs in the world, which has had a negative impact on cognitive and reproductive health.
In the United States, which makes most of the trash, we don't seem to be consuming enough fish for these pollutants to be a problem, according to both new studies. One cannot say that benefits outweigh risks for all people, though.
Keepers and throwbacks
Disregarding sustainable catch issues for now, as both studies did, there are several fish that are high in omega-3s and low in pollutants. These include anchovies, Atlantic mackerel and herring, farmed oysters, sardines, and wild coho, sockeye and pink salmon.
Salmon catches from Alaska are sustainable, but catches from the Pacific Northwest and Atlantic are less so. Among the most polluted fish are Chilean seabass, grouper, rockfish, shark, bluefin tuna, swordfish, tilefish and king mackerel. Polluted is a relative term, however, because these fish have dioxin levels similar to land animals.
Excellent overviews are available from Monterey Bay Aquarium and Ocean's Alive.
Healthy fish made worse
Surprisingly, both fish studies left out two important factors: fish preparation and alternative sources of omega-3s.
You can tell Americans to eat more fish, but the advice could backfire given the typical American diet, with most fish breaded and deep-fried in saturated fat or served with fat-laden mayonnaise. Good fish needs only the lightest seasoning and cooking time.
Two excellent sources of omega-3 fatty acid are walnuts and flax seed. The latter is particularly potent, although for best effects one should buy the seed whole, grind it, and sprinkle it on food because it is largely indigestible otherwise. Hey, you might like it better than anchovies.
Christopher Wanjek is the author of the books “Bad Medicine” and “Food At Work.” Got a question about Bad Medicine? Email Wanjek. If it’s really bad, he just might answer it in a future column. Bad Medicine appears each Tuesday on LIveScience.
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Christopher Wanjek is a Live Science contributor and a health and science writer. He is the author of three science books: Spacefarers (2020), Food at Work (2005) and Bad Medicine (2003). His "Food at Work" book and project, concerning workers' health, safety and productivity, was commissioned by the U.N.'s International Labor Organization. For Live Science, Christopher covers public health, nutrition and biology, and he has written extensively for The Washington Post and Sky & Telescope among others, as well as for the NASA Goddard Space Flight Center, where he was a senior writer. Christopher holds a Master of Health degree from Harvard School of Public Health and a degree in journalism from Temple University.