Up Close & Edible: Tuna

The first question that comes up when discussing tuna's nutritional value is an important one: does this humble fish contain dangerous levels of mercury? Yes, tuna has small amounts of mercury, which can result in health problems, depending on how it's consumed. But dietitians say that avoiding tuna altogether is a mistake. Instead, we should be eating tuna in moderate amounts because it's still one of the easiest and cheapest ways to get protein and health-boosting fish oils into a balanced diet. This advice was bolstered by a study in the February issue of The Lancet, a British medical journal, which indicated that the nutritional benefits of seafood outweigh any toxic effects of trace contaminants like mercury.

Despite the current qualms over mercury, tuna is an American staple. But it's a surprisingly new addition to the menu in the United States. Prior to 1903, sardines accounted for most of the canned fish market, but when the supply took a dive in the early 20th century, entrepreneur Albert P. Halfhill decided to pack empty sardine cans with albacore tuna. Within a decade, the fish once considered a nuisance, reeled in enough interest for 13 factories to produce 115,000 cases of the fish a year. Tuna soared in popularity during World War I, when the fish answered the call for a simple, transportable protein to send to troops abroad. By 1954, the United States had become the largest producer of canned tuna.

Americans today collectively eat 1 billion cans of tuna a year, accounting for one third of the world's catch. Yet the controversy over eating it is feistier than ever. Since all fish contain mercury—an organic element that in significant amounts can cause numbness, memory problems, blindness and other symptoms—the Food and Drug Administration (FDA) recommends no more than 12 ounces of various types of fish every week. Some lobbyist groups call the government advisory too gentle and advocate for stricter recommendations, as well as bolder warning labels; other sources, such as the Lancet report, suggest consumers aren't eating enough fish.

Dietitians say well-managed portions of the fish offer high-quality protein and omega-3 fatty acids—the healthy fats that reduce the risk of death, heart attack, dangerous abnormal heart rhythms and strokes. "The benefits of eating fish outweigh the risks—so you eat it," says Dawn Jackson Blatner, registered dietitian and spokesperson for the American Dietetic Association. "Tuna is one of the easiest fishes to get in our diets." Food producers are responding to positive research by adding omega-3 fatty acids to nonfish food products. But tuna provides a unique natural combination of high-quality protein, convenience, affordability, low saturated fat and high omega-3 fat.

To mitigate mercury worries, stay within the FDA's recommended 12 ounces and vary that weekly portion with a variety of fillets, not just tuna. "Twelve ounces of fish a week is about two fish meals," Blatner says. "Make sure one is a quick thing of canned tuna and one is out at a restaurant getting a fish—not fried—and that covers the 12 ounces."

Nutritionally, it doesn't matter whether the tuna is canned, cooked fresh or raw. The more important choice is the type of tuna. Generally, the bigger the fish, the more mercury it retains. This means that raw tuna (sashimi or sushi) and canned albacore, which come from heftier swimmers, have more potential for poisons than the light chunk tuna in water. "The idea is that mercury is going to be in fish," Blatner says. "And mercury is not great for humans to consume in large amounts, so our goal is to choose fish that is lowest in mercury."

Tuna itself may offer a lean meal—but sometimes the add-ons, like mayonnaise, do not. Luckily, cutting unnecessary calories from old favorites is easy. Fish in oil adds about 110 calories a can, so reach instead for water-based alternatives. Choose a reduced-fat mayonnaise for your tuna salad (just 1 tablespoon of regular mayonnaise unleashes 49 calories and almost 5 grams of fat) or substitute the traditional condiment with a light salad dressing.

Some groups do need to pay extra attention to their fish intake. According to the FDA, pregnant women, nursing mothers and children under 12 should be especially careful in monitoring their fish consumption because they're more vulnerable to mercury poisoning. This group should avoid shark fish, king mackerel, tile fish and swordfish entirely. The best specific guidelines should come from your physician. "There are very few black and white issues, especially in terms of nutrition," says Jennifer K. Nelson, registered dietitian and director of Clinical Dietetics at Mayo Clinic in Rochester, Minn. "Risks and benefits need to be considered not only for tuna, but for basically all types of food. The healthiest diet is one that's balanced—you're not eating excessively of one thing to the elimination of others."

For more information about mercury and fish, visit the FDA's Web site.