Studies have shown that eating half a grapefruit before each meal will help you shed extra pounds. Some believe the vitamin C present in grapefruit leads to weight loss, while others say the fruit naturally boosts metabolism. Tangy fruit like grapefruit also can lower insulin, a fat-storage hormone, and has very few calories. Grapefruit is also a good source of protein, is high in fiber and contains about 90% water. This helps fill you up so you eat less. Try eating half a grapefruit before breakfast and the other half before lunch to lose weight quickly.