One medium apple is low on calories (only 80!) but heavy on quertecin, a powerful antioxidant that protects brain cell degeneration, which can lead to Alzheimer’s disease. Adults who eat apples are less likely to develop high blood pressure, according to one study. Apples can also lower cholesterol and prevent colon cancer, as well as promote healthy teeth and weight loss. Don't forget to eat the skin, too—it’s especially rich in disease-fighting compounds like flavonoids, which reduce the risk of heart disease.