Tuna contains iron, potassium, and B vitamins. Plus, it's an excellent source of selenium, a trace mineral that acts as an antioxidant and may reduce your risk of heart disease and other chronic condition. Tuna is incredibly nutritious and packed with protein, healthy fats and vitamins but it should not be consumed every day. The FDA recommends that adults eat 3–5 ounces (85–140 grams) of fish 2–3 times a week to get enough omega-3 fatty acids and other beneficial nutrients.