Polyphenol-rich foods like grapes may help protect against metabolic syndrome. Grape polyphenols, in particular grape seed polyphenols, may help improve:

cholesterol profile
blood pressure
blood sugar levels

Grapes are a good source of vitamin K. Vitamin K helps clot your blood. Vitamin K deficiency puts you at risk of hemorrhaging. It may also increase your risk of osteoporosis, although more studies are needed.