Both purple and white grapes are good sources of carbohydrate, primarily fructose, which is an easily digestible, simple sugar. One cup of grapes provides about 23 grams of sugar, along with a small amount of protein and a trace of fat. Grapes also contain several important minerals, including calcium, potassium, phosphorus and small amounts of magnesium, iron and zinc. They also provide vitamins C, A and K, and several B vitamins, including folate, thiamin, riboflavin, niacin and vitamin B6. Finally, grapes are a good source of dietary fiber, with more than 1 gram in each cup. Consuming a fiber-rich diet helps keep you regular by adding bulk to your food and making your stool soft; it may also reduce your risk of heart disease and Type 2 diabetes.