If you're confused about whether you should be eating more fish because of its nutrients, or avoiding it because of mercury, one food scientist at Purdue may be able to help. This ScienCentral News video has more.
Mercury and Omega-3s
Eating fish is a healthy choice because it's one of the best sources of beneficial fats called omega-3 fatty acids. But some people are also cautioned to watch out for certain fish because of high levels of mercury.
"The problem with mercury is, if it's ingested at very high levels, for certain populations it can cause damage to our nervous systems," says Charles Santerre, associate professor of foods and nutrition and food science at Purdue University. "Our greatest concern is women of child-bearing age, because women who become pregnant or are nursing can pass mercury either through the placenta or through their milk, and the levels that get to the fetus or the nursing infant can be high enough, in some instances, to cause injury to the baby."
Santerre used a mercury analyzer to test over 250 cans of fish, including five brands of tuna, two brands of salmon, and two brands of mackerel for mercury. (The four types of tuna were light tuna in water, light tuna in oil, white/albacore tuna in water, and white/albacore tuna in oil.) He also tested them for levels of omega-3s. He found that salmon and mackerel were lower in mercury and higher in omega-3s than tuna, and that white/albacore tuna tended to have higher levels of mercury than chunk light tuna, though the white/albacore was also higher in omega-3s. "There are types of tuna, for us it was chunk light tuna in water, that had extremely low levels of mercury, as low as you would find in a salmon or mackerel product," he says. "We would recommend that these be eaten by pregnant women, nursing women, young children." Santerre says the albacore tends to be higher in mercury because, "as I understand it, they'll be an older fish, maybe a different species, and so they'll be exposed to mercury throughout their life and so they'll accumulate more."
image: ABC News
The U.S. Tuna Foundation points out that the FDA and EPA say it's safe for pregnant women to eat up to six ounces of albacore a week, and that 98% of Americans already consume less than that (an average sandwich has two ounces). Santerre's recommendation for albacore tuna is more conservative than the government's—four ounces a week.
Santerre cautions that even women who might become pregnant are considered part of the sensitive population. "A woman that may become pregnant must understand that mercury can stay in her body for up to a year, so it's very important for her to take steps prior to her becoming pregnant to keep the mercury out of her body," he explains, but stresses that people should not be scared away from eating fish. "It's very important that people eat fish. We recommend about 8 ounces of fish a week to get those healthy nutrients that are found in fish, so that's very important. For pregnant, nursing women, young children, be careful about which fish you incorporate in to the diet. We recommend fish that's high in omega-3s and low in mercury. Salmon…is a very good choice, rainbow trout is another good choice, shrimp is a reasonably good choice."
Santerre, who is also a food science communicator with the nonprofit Institute of Food Technologists, says that more accessible mercury testing is in our future. "One of the revolutionary things that's occurred in the last three or four years is we've gotten better ways, faster ways of measuring mercury in fish," he says. "The mercury analyzer is capable of testing hair, cuticles and blood and potentially milk, so at some point we will have more widely available testing of mercury that people will have access to."