Grapes are a moderate source of calories. Each cup has 104 calories, which means you can enjoy one to two cups as a moderately sized snack. Most of those calories come from carbohydrates, and each cup of grapes contains 27 grams of total carbs, including roughly 1.5 grams of fiber. Like most fruits, grapes have very little protein and fat – 1 gram and a quarter-gram per serving, respectively. Since carbs are your body’s preferred source of energy, green grapes can be a healthy way to get a little energy boost, even if they don’t have the most well-rounded nutritional profile.