Eating a variety of lean proteins such as fish can help with weight loss and provide important nutrients like brain-boosting omega-3’s. However, you’ve likely heard you shouldn’t overdo it on fish because of the mercury content. While there are multiple forms of mercury, “the type that’s often found in fish is known as organic methylmercury,” says Laura Tiu, PhD, a marine science extension agent with the University of Florida Sea Grant.
Mercury from industrial activities is converted by bacteria into methylmercury in aquatic environments like streams, lakes and oceans. “These bacteria form the bottom of the food chain, and they’re gobbled up by small fish, which are in turn eaten by larger predators like shark and albacore tuna, mercury doesn’t just go away — it accumulates in their bodies,” explains Tiu.
“Most, if not all, fish contain at least some amount of mercury,” says Amanda A. Kostro Miller, RD. For your health, a good rule of thumb is to avoid or limit high-mercury fish and consume mostly low-mercury fish. Limit larger, high-mercury fish like king mackerel, marlin, orange roughy, swordfish, tilefish, ahi tuna and bigeye tuna. Instead, opt for smaller, lower-mercury fish like sardines, trout, wild and Alaskan salmon, flounder, tilapia, cod, whitefish and anchovies (though the latter can be high in sodium).
Here’s what you need to know about mercury in fish and how to minimize exposure while still reaping the health benefits from seafood.
In most cases, fish is the most common way you’re exposed to mercury on a day-to-day basis, says Dr. Melinda Ring, executive director of Osher Center for Integrative Medicine at Northwestern University. If you eat too much mercury, it can build up in critical organs like your brain and kidneys, leading to troubling symptoms like fatigue, headaches, memory and concentration issues, plus problems with speaking and coordination. It’s also important for pregnant women, newborns and small children to limit their exposure.
It’s important to keep in mind that exposure to very high levels of mercury that would cause these health issues is rare, says Tiu. For most of us, the risk of eating mercury-exposed fish isn’t a concern. In fact, studies show the benefits of eating fish generally exceed the risks for adults. Fish are a great source of protein, the best natural source of vitamin B12 and vitamin D, and also provide iron and minerals like selenium, zinc and iodine.
In particular, fatty fish like wild-caught salmon, mackerel, herring and trout are also high in docosahexaenoic acid (DHA), a type of omega-3 fatty acid linked to an improved memory and learning ability, lower rates of cognitive decline and even a reduced risk of heart disease. Fatty fish are encouraged in the Mediterranean diet, which is often ranked as one of the healthiest.
Whether you prefer canned, farmed or wild-caught fish depends on your personal budget, taste and environmental preferences. There are safe options for each in terms of mercury, but it depends on the type of fish. Remember, “larger fish with longer life spans tend to carry lots of mercury they’ve accumulated from eating smaller fish lower on the food chain. On the other hand, smaller fish tend to be lower in mercury,” says Kostro Miller.
In particular, when you’re shopping in the canned fish aisle, pay attention to the type of tuna you’re getting, says Dr. Ring. There are two main kinds of canned tuna: chunk light (typically skipjack tuna) and solid or chunk white (albacore tuna). Mercury levels in albacore tuna are almost three times higher than in smaller skipjack tuna, so opt for skipjack tuna or another lower-mercury option like sockeye or pink salmon from Alaska, she says.
If you tend to eat freshly caught fish, check local advisories from the Environmental Protection Agency (EPA) to make sure your catch is safe to eat. If there is no advisory, limit yourself to one serving a week.
While mercury in fish can sound scary, you don’t want to miss out on the benefits of eating fish. “For a healthy diet, aim to eat at least 8 ounces of fish every week (such as two meals with 4-ounce or fist-sized servings of fish) and opt for healthier prep methods like baking, poaching or grilling,” she suggests.
If do you tend to eat a high-fish diet (such as Asian, Pacific Islander and Native American diets), consider asking your doctor to check your mercury levels. Similarly, if you’re pregnant, breastfeeding or wondering how much fish your children should eat, consult with your doctor for guidance. While some fish are best limited or entirely avoided due to their high mercury content, if you’re expecting or nursing, you’re still advised to get in at least 8 ounces and up to 12 ounces (or 2–3 servings) of low-mercury fish per week to support overall health.
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