NBC News - Tuna is one of the most convenient protein sources that exists, so it can easily become a go-to lunch. But is it safe to eat it every day?
The short answer: Probably. But if you're wrong, you could end up with mercury poisoning, which can cause weird symptoms like tingling sensations and loss of balance, says Michael Gochfeld, M.D., Ph.D., a researcher with the Environmental and Occupational Health Sciences Institute.
"It would likely be safe for many men to eat tuna every day, while some men could experience symptoms of mercury toxicity from eating the same amount," says Food and Drug Administration spokeswoman Lauren Sucher.
Here's why it's so complicated: You have to balance the benefits of eating fish with the risk from mercury, while taking into account a person's weight, their sensitivity to mercury, the type of tuna, and how much risk you're willing to take, says Dr. Gochfeld.
Nearly all seafood contains traces of mercury, according to the FDA. So the question is: At what level does mercury become poisonous?
That's where it gets even more confusing. No one knows exactly where mercury goes from being harmless to toxic, because you'd have to poison people to find out, says Men's Health nutrition advisor Alan Aragon, M.S.
Most experts can agree on at least two facts, though.
1. Fish is good for you.
Research has shown that it may lower your risk of heart disease, stroke, obesity, cognitive decline, depression, cancer, inflammatory disorders, and asthma, says Dariush Mozaffarian, M.D., Dr.P.H., dean of the Friedman School of Nutrition Science and Policy at Tufts University. Restricting your fish intake could make you miss out on all those benefits.
2. The risks from mercury have been overhyped.
Mercury can harm the developing nervous systems of fetuses and young children, according to the FDA. But when the agency warned pregnant women to limit consumption of high-mercury fish in 2004, it set off unnecessary panic for everyone else, Dr. Mozaffarian says.
Pregnant women should avoid canned tuna: report
The truth is, those warnings never applied to the general public. However, it is possible for adults to get mercury poisoning. You just have to eat a lot of high-mercury fish for that to happen.
Our advice: Almost all guys will be perfectly fine eating a can of light tuna four times a week.
If you want to eat more tuna, or different types of tuna, you can calculate your weekly limit by following the instructions below. And if you do experience symptoms of mercury poisoning, you can usually reverse them by eating less fish or eating only low-mercury fish, says Dr. Gochfeld.
1. Pick your tuna.
An average 5-ounce serving (1 can) of light tuna contains 18.11 micrograms of mercury. An average 5-ounce serving (1 can) of albacore tuna contains 49.53 micrograms of mercury. An average 5-ounce serving of tuna steak or tuna sushi could contain up to 97.49 micrograms.
2. Convert your weight to kilograms by dividing your weight in pounds by 2.2.
3. Divide the amount of mercury from Step 1 by your weight in kilograms from Step 2. The result is your mercury dose (in micrograms) per kilogram for a 5-ounce serving.
4. Pick a mercury dose limit from the two main federal recommendations. One is very conservative, the other is less so.
You could go with the Environmental Protection Agency dose, which is safe enough for the most vulnerable people--including pregnant women. That dose is .1 microgram per kilogram per day.Or go with the Centers for Disease Control and Prevention, which says consuming .3 micrograms per kilogram per day of mercury poses minimal risk.
5. Multiply your chosen daily limit by 7 to find your weekly limit. (For the EPA it's .7; for the CDC it's 2.1.)
6. Divide your weekly limit from Step 5 by your dose from Step 3 to find how many 5-ounce servings you can have per week. If you're a 180-pound guy eating light tuna, you could safely eat 9.5 five-ounce cans according to the CDC, or 3.2 five-ounce cans according to the EPA.