IN BRIEF This article reviews the impact of exercise on weight loss and weight maintenance and the possible reasons that weight loss outcomes resulting from exercise are not consistently realized. Energy balance is a process through which the body attempts to establish homeostasis. Most individuals spend much of their lives in the same weight range without daily focus on caloric intake and output. Physical activity and exercise are often used interchangeably. However, correctly defined, physical activity is all movement that creates energy expenditure, whereas exercise is planned, structured physical activity 1.