The reasons for yo-yo dieting are varied but often include embarking upon a diet that was initially too extreme. At first the dieter may experience elation at the thought of loss and pride of their rejection of food. Over time, however, the limits imposed by such extreme diets cause effects such as depression or fatigue that make the diet impossible to sustain. The dieter reverts to their old eating habits, and with the added emotional effects begins to rapidly regain weight.
This kind of diet is associated with extreme food deprivation as a substitute for good diet and exercise techniques. As a result, the dieter may experience loss of both muscle and body fat during the initial weight-loss phase (weight-bearing exercise is required to maintain muscle). After completing the diet, the dieter is likely to experience the body's famine response, leading to rapid weight gain of only fat. This is a dangerous fat-cycle that changes the body's fat to muscle ratio, one of the more important factors in health.