Calories

• One half of a medium-sized grapefruit, the standard serving size, has 40 calories. A whole medium-sized grapefruit, therefore, has 80 calories.
  
  

Fat, Cholesterol and Sodium

• Like most fruits, grapefruits contain no fat, cholesterol or sodium.
  
  

Carbohydrates

• One half-grapefruit contains 10 grams of carbohydrates, 1 gram of which is dietary fiber and the other 9 grams of which are sugars.
  
  

Protein

• A half a grapefruit contains just 1 gram of protein.
  
  

Vitamin C

• Grapefruits are packed with vitamin C. A half of a grapefruit contains 70 percent of the recommended daily allowance for this vitamin.
  
  

Potential Drug Interactions

• People taking certain cholesterol-lowering medications, calcium channel blockers and other types of drugs should not eat grapefruit or drink grapefruit juice, because of possible negative drug interactions. A physician or pharmacist can clarify whether it's okay to consume grapefruit while taking a particular medication.