Often confused with yams, these tubers are one of the healthiest foods on the planet. In addition to countering the effects of secondhand smoke and preventing diabetes, sweet potatoes contain glutathione, an antioxidant that can enhance nutrient metabolism and immunesystem health, as well as protect against Alzheimer’s, Parkinson’s, liver disease, cystic fibrosis, HIV, cancer, heart attack, and stroke. What’s more, they’re also loaded with vitamin C, which smoothes out wrinkles by stimulating the production of collagen. A recent study in the American Journal of Clinical Nutrition found that volunteers who consumed 4 milligrams of C (about half a small sweet potato) daily for 3 years decreased the appearance of wrinkles by 11 percent.