There's no question that you are getting mixed messages on tuna, a saltwater fish that can range anywhere in size from around four pounds to upwards of 1,500 pounds, depending on the species. While U.S. dietary guidelines for Americans 2020-2025 recommend adults eat two servings of fish weekly (pregnant and breastfeeding women should eat up to three servings), tuna and other ocean fish may contain trace amounts of mercury, which is not healthy.
Healthy Nutrition From Tuna
Tuna, for its part, is a source of high-quality protein with very little saturated fat. It contains all essential amino acids required by the body for growth and maintenance of lean muscle tissue. Fresh and canned tuna supplies omega-3 fats, which are heart-healthy, and which are necessary during pregnancy and infancy for brain and visual development. Tuna is also an excellent source of vitamin B12 and selenium.
Mercury Concerns and Tuna
For most healthy adults, eating tuna once or twice a week doesn't present a health concern. However, experts suggest that women in their childbearing years, who are pregnant or nursing, and young children all limit their tuna intake. One species, bigeye tuna, should be avoided entirely. That's because mercury can be especially toxic to a developing child's nervous system. The risk is dose-dependent, meaning that babies and children exposed to more mercury are more at risk for problems. Mercury can pass between a mother and her unborn baby.
If you're pregnant or nursing, you should limit your consumption of tuna, and if you have a baby or young child, you should limit that child's consumption.
How Much Tuna is Too Much?
According to 2017 guidelines from the U.S. Food and Drug Administration (FDA), women who are pregnant or nursing, planning to become pregnant, or babies and young children should completely avoid seven types of fish that are extremely high in mercury: shark, swordfish, king mackerel, marlin, orange roughy, tilefish (from the Gulf of Mexico) and bigeye tuna. Something else you may want to consider is that light, canned tuna has far less mercury than canned, white albacore tuna.
Women who are at risk can eat up to 12 ounces (two servings) per week of fish and shellfish known to be lower in mercury content. These include canned light tuna, shrimp, salmon, pollock, and catfish. They should, however, limit themselves to around 4 ounces (one serving) per week of Albacore/white tuna (canned, fresh, or frozen) and yellowfin tuna. This is the amount that a small (5.5 ounces) can of tuna yields after draining. The FDA says children can eat 1 ounce at age 2, and increase with age up to 4 ounces at age 11.
Canned light tuna has less mercury than canned white tuna.
The bottom line is, tuna (like most things) is good in moderation and not good in excess. If you enjoy tuna, you can include it as a healthy food in your diet. Just make sure not to overdo it, especially if you fall into one of the at-risk groups.
Advice About Eating Fish. U.S. Food and Drug Administration
Fish, tuna, light, canned in water, drained solids. Fooddata Central, United States Department of Agriculture
Questions & answers from the FDA/EPA advice about eating fish for women who are or might become pregnant, breastfeeding mothers, and young children. FDA. Published online March 9, 2020.
Centers for Disease Control and Prevention. Mercury. Updated August 27, 2019.
FDA and EPA Issue Final Fish Consumption Advice. US Food & Drug Administration
Bashiri Dezfouli, Ali et al. Evaluating Total Mercury and Methyl Mercury Contents in Canned Tuna Fish of the Persian Gulf. Iranian journal of pharmaceutical research : IJPR vol. 17,2, 2018