For decades, nutrition experts promoted fish as an important food for brain and heart health. Many types of fish and shellfish are extremely low in fat, most are very low in cholesterol, and even fatty fish like salmon, trout, and tuna contain fats that are beneficial. Fish was the healthful alternative to beef, pork, and eggs.
But then came the warnings: Researchers found that some fish are high in mercury, which has been linked to poor performance on cognitive tests, and other toxic chemicals. Instead of eating fish, we were told to avoid it!
To make things even more confusing, some recent studies have indicated that the mercury in fish might not affect our bodies as much as previously thought. Other studies indicated that fish oil—a major source of heart-healthy fats—might not even be all that beneficial.
When it comes to fish, what are the facts?
Unlike the fat in most animal products (including dairy), fatty fish are high in fats that provide health benefits. In fact, fatty fish are actually good for the heart! And modern science backs up the old wives tale about fish as brain food. Fatty fish are one of the few dietary sources of vitamin D; a recent study found a strong link between vitamin D deficiency and dementia risk. Another recent study conducted by researchers at UCLA found that adults with lower levels of omega-3s had lower brain volumes (which is associated with brain aging) and scored lower on tests of visual memory and executive function. Omega-3s may also protect the neurons in the brain and spine and reduce the risk of developing Lou Gehrig’s disease.
Some studies have shown little to no difference in cognitive performance in subjects who took fish oil supplements or a placebo. However, the UCLA study showed older adults who ate baked or broiled fish were less likely to have problems with short-term memory. Fish has also been shown to protect against alcohol-induced dementia.
Why the discrepancy? There are a few possibilities: The protective benefits from fish may develop over time, so people who have made it a regular part of their diets show benefits when those who take supplements for a short time don’t. Or it could be that there are other compounds in fish that work to boost the effects of the omega-3s. Or it could be that getting the fish oil from a pill means your diet includes other, possibly less beneficial, types of protein.
A study in England followed more than 14,000 women who were pregnant in 1991 and 1992, and monitored their and their children’s health and development. One aspect of the study sought to determine how different foods contributed to blood mercury levels. Researchers found that a little less than 20 percent of the mercury in blood was due to diet, and that fish, oily fish, and shellfish accounted for 7 percent of total blood mercury.
Pollutants like mercury, dioxin, and PCBs accumulate in a fish’s body over time, so older fish and predatory fish are more likely to contain them.
Eating fish two to four times a week, of portions that are four to six ounces, is enough to get the benefits. Just be sure to switch up your choices. Consuming a variety of foods means you get a wider range or nutrients, and if you are concerned about chemicals or pollutants, you can lessen your exposure. One way to remember which fish are fatty is by the acronym SMASH, or SMASH T: Salmon, Mackerel, Anchovies (sometimes A stands for Arctic char), Sardines, Herring, and Trout.