Energy-balance

Weight loss is determined by multiple interacting factors — energy balance, metabolic rate, hormonal environment, sleep, psychological adherence, and genetics. This article examines each with clinical evidence, explaining why identical calorie deficits produce different results in different people.

Diet contributes more to weight loss through calorie deficit than exercise in most contexts, but exercise has specific benefits diet cannot replicate: lean mass preservation, metabolic rate maintenance, and long-term weight maintenance. This article reviews the evidence for both.