Think of grapefruit (one of the best fruits for fat loss) as your breakfast appetizer. “Even if you changed nothing else about your diet, eating half a grapefruit before each meal may help you lose up to a pound a week,” says Patricia Bannan MS, RDN, author of Eat Right When the Time Is Right. “Researchers found that when obese people ate half a grapefruit before each meal, they dropped an average of 3.5 pounds over 12 weeks,” she says. How’s it work? The tangy fruit helps lower insulin, a fat-storage hormone. It’s also 90% water, so it fills you up so you eat less, explains Bannan.