Nature's Bounty Metabolism Booster features a clinically studied blend called Sinetrol®. This ingredient is a combination of grapefruit, sweet orange, blood orange, and guarana extracts. It works by stimulating lipolysis, the body's natural process of breaking down stored triglycerides (fat) into free fatty acids to be used for energy. This "metabolism-boosting" effect helps your body burn fat more efficiently when combined with a healthy diet and regular exercise.