Whenever I participate in conversations about increasing fish consumption, the first thing that comes up is almost always mercury. People are terrified of mercury. Nobody seems to have any concern about exceeding the USDA recommendation for sodium, fat, or sugar every day. Yet, as soon as we discuss fish, everyone becomes strictly health conscious, and most people I talk to seem to be experts on the topic. So, am I saying you should disregard the FDA recommendation for seafood and eat fish with no regard for mercury risk? Of course not, but let’s put it in perspective a little.
For seafood, mercury is the most commonly mentioned toxin and is present in many types of fish. Symptoms of mercury poisoning include memory loss, itching, swelling, difficulty speaking, and vision or hearing problems. In seafood, mercury comes in the form of methylmercury, which is introduced into aquatic systems by microbes. As part of their life cycle these microbes produce methylmercury from environmental mercury which is present in the substrate. This compound enters the food chain through surface absorption by plants and plankton. These are eaten by small fish which are then eaten by larger fish. At each stage of the food chain, the mercury becomes more concentrated in a process called bioaccumulation. In simple terms, larger carnivorous fish will have more mercury than fish further down the food chain. Within a species, larger and older fish will have more mercury than smaller ones. Overconsumption of mercury from fish can cause dangerous mercury levels in humans, however, this is easy to manage by eating a diet composed mostly of low mercury species.
Fish are a great source of low fat protein and Omega 3 fatty acids like DHA and EPA. They provide a good source of many micronutrients like selenium, zinc, iron, vitamins A, B, and D. For this reason, the EPA advises most Americans do not eat enough fish and should increase their consumption. Here is their document on the topic:
It contains a handy chart on the second page that is targeted toward pregnant women. Women who are pregnant, breast feeding, or planning/risking becoming pregnant should follow this advice strictly. Others should generally stick to it, but keep in mind that not all fish are created equal and mercury varies widely. The FDA acknowledges this in the 2015-2020 Dietary guidelines, with this statement:
Individuals who regularly consume more than the recommended amounts of seafood that are in the Healthy U.S-Style Pattern should choose a mix of seafood that emphasizes choices relatively low in methyl mercury.
Here is their chart that shows the concentrations of mercury by species. If you want to look for your favorites, you can click on the header to sort alphabetically. The default sort is by mercury concentration.
Scallops, the best on the list, contain almost no mercury. The worst species for mercury, Tilefish, contain 37 times more mercury than scallops. So, if you have a dietary situation that requires you to eat more fish than the recommendation, for example, you are a pescatarian that needs a lot of protein to maintain your weight, eating more than 12 ounces of scallops a week is relatively safe option. I always try to maintain a wide variety of species from varying bodies of water in order to reduce my risk of overdosing on any particular contaminant. Some other seafood options that are low in mercury are shrimp, clams, oysters, sardines, tilapia, anchovies, and salmon. There are another 40 choices that are relatively low in mercury. You should check with your doctor if you plan to eat 14 servings a week of fish. Otherwise, just know that for mercury, the recommendation for Spanish mackerel is not more than 4 ounces per week. For a common fish from the good list like cod, the same amount of mercury can be found in 16 ounces. If you wanted to eat fish every day, a serving each of scallops, shrimps, clams, salmon, catfish, pollock, and crab would not add up to ½ the amount of mercury in that one recommended serving of Spanish mackerel.
Making dietary decisions is hard and there is a lot of conflicting information out there. In the case of mercury, much of it is based on fear rather than fact. The fears are founded in reality, but they are certainly exaggerated and much of the available advice is misguided. I encourage you to use real data from trusted sources like the EPA, FDA, USDA, and the Department of Health and Human Services to make your decisions rather than sensationalized click-bait from Facebook. Focus on the main point of their advice which is to eat more seafood and vegetables with less meat and processed food. According to many different studies, a diet on the high end of the recommendation can help you be leaner, healthier, and just a little bit smarter.