[N]o matter what those contrived weight-loss infomercials say, losing weight itself is strictly a numbers game. "It's all about calorie deficits," says Jana Klauer, M.D., a weight-loss expert in private practice and research fellow at St. Luke's - Roosevelt Hospital in New York. That is, burn more calories than you consume, and you will lose weight. More specifically, for every 3,500 calories you burn over and above what you take in, you'll lose 1 pound. All the diet gimmicks in the world won't get you around these hard numerical truths.