Red cultivars are sweeter and provide more of the required daily intake of vitamin A. They are also an excellent source of folic acid, vitamin B12, magnesium and fiber.

More specifically, a medium grapefruit contains:
• Calories: 52 cal
• Carbohydrates: 13 grams
• Protein: 1 gram
• Fiber: 2 grams
• Vitamin C: 64%
• Vitamin A: 28%
• Potassium: 5%
• Vitamin B1 (Thiamine): 4%
• Folic Acid: 4%
• Magnesium: 3%

Regular consumption of grapefruit appears to be beneficial for the immune system. As an example, a whole grapefruit contains about 80 micrograms of vitamin C, which is more than you would get from a large orange.