Grapefruit is number 1 in the fight against excess weight because of its powerful fat-burning qualities. Grapefruit enzymes help actively process calories. No calorific meal (no more than 800 kcal) will damage your figure if you eat half a grapefruit with it.
Bananas, though, are the most “energetic” fruit. They digest slowly, and scientists recently found certain substances in them that block the activity of cells responsible for fat splitting.