Can Eating Tuna Every Day Be Harmful?

The American Heart Association recommends eating omega-3-rich fish, such as tuna, twice a week for good health. It's wise, however, to vary what you choose. Because tuna is a source of mercury, you should avoid eating it daily, especially higher-mercury varieties like albacore tuna. If tuna makes a regular appearance in your diet and you're concerned about how it may affect your health, consult your doctor.

Eating tuna every day may increase mercury levels in your body. (Image: fotomania_17/iStock/Getty Images)

Tuna Nutrition Basics

The 2015 Dietary Guidelines for Americans reports that most Americans don't eat enough seafood. For those trying to increase the seafood content of their diets, tuna makes a convenient choice because it's readily available and fairly inexpensive. Plus, it's low in calories and a good source of protein. A 3-ounce portion of canned light tuna packed in water has 73 calories, 17 grams of protein and less than 1 gram of fat. The same serving of canned white (albacore) tuna packed in water has 109 calories, 20 grams of protein and 2.5 grams of fat. Although a little pricier, fresh yellowfin tuna also makes a healthy choice with 111 calories, 25 grams of protein and less than 1 gram of fat per 3-ounce cooked portion.

Tuna is, however, a source of mercury. A 3-ounce portion of light chunk tuna has 10 micrograms of mercury, and the same-sized serving of canned white or yellowfin tuna has 30 to 35 micrograms.

Dangers of Too Much Mercury from Tuna

Mercury is a poisonous metal that can have serious health consequences, such as injury to the brain, heart, kidneys and lungs. It's especially harmful to children and pregnant women because it can affect development of the child and growing fetus. Adults can safely consume 21 micrograms of mercury a day, according to the Environmental Protection Agency. Children should be fed even less. According to the Natural Resources Defense Council, air pollution from coal-burning factories is the major cause of mercury in the environment. Rainfall transfers the mercury pollutant to the water where it is absorbed by the fish. Larger fish like tuna tend to have higher concentrations of mercury because they get it not only from the water, but from the fish they eat.

How Much Tuna is Safe?

You don't have to avoid tuna altogether, but you shouldn't eat it every day. The type of tuna you choose also determines the amount that's safe to eat. Children under 6 years of age should be fed not more than 3 ounces of white or fresh tuna a month and children ages 6 to 12 not more than two 4.5-ounce portions a month. Women, pregnant or not, can have up to 18 ounces of white or fresh tuna a month, and men up to 24 ounces.

Because it has less mercury, you can eat more canned light tuna. Children 6 and younger can have up to 9 ounces of canned light tuna a month. Older children and adults can have up to 24 ounces -- or one 3-ounce serving per week -- of canned light tuna.

Serving Healthy Tuna and Lower-Mercury Fish

If you're buying canned tuna, select tuna packed in water to cut calories. If you're making a tuna salad, use small amounts of mayonnaise and add plenty of veggies such as diced celery, peppers and carrots. Also, consider replacing mayonnaise with nonfat yogurt. Toss any remaining tuna salad or open can of tuna after 24 hours.

For fresh tuna, select fish that has no discoloration or strong odor and cook within a day of purchase. Pat your fresh tuna dry before cooking, then grill, pan fry or broil until done to your liking, usually about 2 minutes per side.

Also, to get your weekly seafood needs for good health, mix it up. Include different types of fish in your diet that have less mercury but are good sources of omega-3s, such as salmon, anchovies and sardines. Also include other types of seafood or fish, such as shrimp, scallops, tilapia and haddock.

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