According to Brigitte Zeitlin, MPH, RD, a registered dietitian in New York City, tuna is a great source of protein and makes for a great, quick protein addition to your lunch or dinner. However, as with all fish and shellfish, you should keep track of the amount you eat and keep in mind eating too much of it could lead to mercury accumulation. The FDA recommends pregnant women and children eat only up to 12 ounces (or two meals) of light canned tuna a week.
"Mercury poisoning can give you bad headaches, impair your speech, walking, and hearing, slow your cognitive function ,and lead to drastic mood swings, so it's definitely something we want to avoid," said Zeitlin. "It is best to keep your tuna to just one or two meals a week, and supplement with other fish, like salmon, halibut or cod."