Your favorite deli sandwich has a little secret: Selenium. This nutrient helps preserve elastin, a protein that keeps your skin smooth and tight. The antioxidant is also believed to buffer against the sun (it stops free radicals created by UV exposure from damaging cells). Tuna is also a great source of protein, contains no trans fat, and a 3-ounce serving of chunk light contains 11 mg of heart-healthy niacin, which has been shown to help lower cholesterol and help your body process fat. University of Rochester researchers determined that niacin raises HDL cholesterol (the good kind) and lowers triglycerides more than most statins alone.