Exercise appears to play a critical role in the loss and maintenance of body weight. Diet alone has met with only temporary success because metabolic rate is decreased with extreme calorie restriction. This decrease persists after the dieting period has ended, often leading to rapid weight regain and the "yo-yo effect." In some instances, exercise alone has been effective for weight loss; however, success varies according to the gender of the subjects and to the type, intensity and duration of the exercise. Exercise programs of low to moderate intensity, long duration and high frequency seem to be most beneficial, with the most popular forms of exercise being walking/jogging, cycling and swimming. The purpose of this article is to explore the differences between diet and exercise, low vs. high intensity, short vs. long duration, and land vs. water exercise as these differences pertain to weight loss, food intake and energy balance.