Grapes contain many important nutrients. When you bite into a grape, you get more of a batch of sweetness. The skins of black grapes contain the phytochemical resveratrol, which appears to protect against several chronic diseases and conditions. Grapes may soon take their place as the best food for healthy eyes. Grapes are a good source of vitamin K. Vitamin K helps the blood to clot. Vitamin K deficiency puts you at risk of bleeding. It can also increase the risk of developing osteoporosis, although more studies are needed.