Research says fish may be good for the brain, thanks to an omega-3 fatty acid called docosahexaenoic acid (DHA) that's found in fish oil. In fact, a 2015 review of the literature published in Current Opinion in Clinical Nutrition and Metabolic Care suggested a link between these fatty acids and slower brain aging.

Omega-3 Source

But not all fish have equal amounts of omega-3 content, according to a fact sheet provided by the National Institutes of Health. Cold-water fatty fish, such as salmon, mackerel, tuna, and sardines, have higher amounts of omega-3s than fish with a lower fat content—such as bass, tilapia, and cod—and shellfish.

Then again, omega-3 content can be higher or lower depending on what the fish eat. Fish raised on farms tend to have higher levels of DHA than wild-caught fish, but that too depends on the food they are fed. A 2016 study in Scientific Reports found that the level of omega-3s in farm-raised Atlantic salmon from Scotland decreased significantly between 2006 and 2015 after farmers changed the type of feed they used.

Fish Fears

More Americans than ever before are eating fish, according to a 2016 report from the National Oceanic and Atmospheric Administration. The report says per capita consumption is 15.5 pounds of fish and shellfish, which translates to four ounces of seafood (or one serving) a week. Dietary guidelines from the US Food and Drug Administration (FDA) recommend at least eight ounces a week. If fish is so good for us, why aren't Americans eating more of it?

A fear of mercury—a metal found in fish that has been linked to problems in brain development in fetuses and young children—is one of the biggest reasons, says Martha Clare Morris, ScD, professor of internal medicine at Rush Medical College in Chicago. In a 2016 study published in the Journal of the American Medical Association, Dr. Morris found that certain people who ate fish regularly also had higher mercury levels in their brains, but the metal wasn't linked to increased brain neuropathologies.

Mercury on the Brain

Dr. Morris and her colleagues examined 286 postmortem brains, measuring mercury levels and looking for evidence of plaques and neurofibrillary tangles associated with Alzheimer's. The subjects were from a study of 554 now-deceased people who had completed questionnaires about their eating habits (their average age at death was 90, and they'd died an average of four and a half years after filling out the questionnaires). For people with APoE4, a genetic marker that puts them at risk for Alzheimer's disease, eating fish at least once a week was associated with fewer harmful proteins in their brains. And while the level of mercury correlated to the amount of fish they ate, it did not result in increased levels of Alzheimer's plaques and tangles.

"[The study] considerably diminishes concerns about fish/brain toxicity," says Nikolaos Scarmeas, MD, associate professor of clinical neurology at the Vagelos College of Physicians and Surgeons at Columbia University in New York City and at National and Kapodistrian University of Athens, Greece.

Four Fish Tips

The FDA and the Harvard T.H. Chan School of Public Health provide resources for safe fish eating.

The FDA website includes a chart listing which fish are safest to eat, and how much, based on mercury levels. The chart was originally designed for pregnant women, but it's appropriate for the general population.

In addition, Eric Rimm, ScD, professor in the departments of epidemiology and nutrition at Harvard, offers this advice on fish consumption:

1. Avoid shark, swordfish, king mackerel, or tilefish (sometimes called golden bass or golden snapper), which contain high levels of mercury.
2. Aim to eat up to 12 ounces a week of a variety of fish or shellfish low in mercury, such as shrimp, canned light tuna, salmon, pollack, and catfish.
3.  Limit consumption of canned albacore ("white") tuna to once a week. It has more mercury than canned light tuna.
4. Check local advisories about the safety of fish caught in the U.S. If you can't find anything, limit the fish you eat from local waters to six ounces per week.

Read More

For three fish recipes, developed by Linda Monastra, a chef at Sprig and Vine restaurant in New Hope, PA, visit BrainLifeMag.org/FishRecipes.