Certain fish are high in mercury, a heavy metal that’s readily taken up by the body. Mercury is a toxin that’s absorbed by fish through their gills as they swim and through their consumption of mercury-rich plankton. Larger fish tend to be higher in mercury than smaller fish. This is because larger fish consume large numbers of smaller fish that feed on mercury-containing plankton.
Generally speaking, the larger and older the fish, the higher the mercury levels.
Unfortunately, tuna is considered one of the most relevant dietary sources13 of mercury in the world. “Because tuna are higher on the food chain, they tend to retain more mercury in their fats,” climate-focused dietitian Dana Ellis Hunnes, PhD, MPH, RD, tells mindbodygreen. Hunnes explains that mercury is a known neurological disruptor14 and negatively affects the brain, especially in developing fetuses and in young children.
Keep in mind that the mercury in raw tuna is more bioavailable13 to your body than mercury found in cooked tuna, so people who frequently eat raw tuna products, like tuna sashimi, are at an increased risk of developing high mercury levels.
There are also sustainability concerns with fish that lie higher up the food chain, which we’ll get to in detail below.
