Not only do grapefruits have plenty of vitamin C, they also contain naringenin, an antioxidant that appears to cut the risk of developing insulin resistance. Researchers found that mice given naringenin supplements were able to control glucose levels in their blood no matter how much they ate, plus they had lower cholesterol than mice fed a similar diet but without naringenin. Best bet: Grapefruit interferes with the absorption of certain medications, causing higher than normal blood levels of the drug. If you take a medication for high cholesterol or blood pressure, or a neurological, psychiatric or immunosuppressive drug, check with your doctor before adding grapefruit or grapefruit juice to your diet. Other sources: Tomatoes (with their skins), Seville oranges, tangelos Try this: For a refreshing salad, “toss peeled grapefruit sections with chilled crabmeat and fresh mint,” Karen Page recommends.