5 Healthy foods that can be harmful if you eat too much of them

Canned Tuna

It’s cheap, convenient, and packed with protein and those all-important omega-3s. But canned tuna does contain some mercury, which can harm the nervous systems and brains of developing fetuses and young children. Higher amounts of mercury can be poisonous to adults, too (symptoms include numbness or tingling, vision problems, and memory problems). But experts don’t know exactly how much mercury-laden tuna you’d need to eat to get sick.

White albacore tuna contains more mercury than light tuna, and the amount that you can eat depends on your weight. For instance, a 110-pound person should stick to less than four ounces of white albacore tuna or nine ounces of light tuna per week. But a 165-pound person can have five ounces of white albacore tuna or 14 ounces of light tuna per week, according to calculations from Consumer Reports. (FYI, a can of tuna is five ounces.)

If you’re pregnant, breastfeeding, or trying to conceive, stick with the FDA’s established guidelines: Enjoy up to 12 ounces of lower mercury seafood per week, like shrimp, salmon, catfish, or light tuna. For higher mercury albacore tuna, limit yourself to no more than 6 ounces per week. (And stay away from these 12 fish altogether.)