There are approximately 100 calories in a single cup of red grapes. There are also about 1.4 grams of fiber per portion, which aids in regulating blood sugar.
Though white grapes are generally considered healthy, it's the dark skin of red grapes that provides the most health benefits. Red grapes are packed with antioxidants and phytonutrients, which reduce the chances of developing cancer. They also include quercetin extract, which is most known for its antihistamine and anti-inflammatory effects. Both red and white grapes contain a significant amount of manganese; a single cup harbors about 33 percent of the recommended daily intake.