According to The US National Task Force on the Prevention and Treatment of Obesity, weight cycling or “yo-yo dieting” carries psychological and physiological health hazards.
1. The amount of fat stored in the body increases with each cycle of up-and-down dieting. When a person loses weight, both fat and muscle tissue are shed. When the weight is put back, however, it tends to be made up of a greater proportion of fat and less muscle, leaving the person “fatter” than ever. Besides, a history of loss and gain is associated with greater amounts of fat stored in the abdomen, a pattern of fat distribution linked to greater risk of heart disease and diabetes.
2. Yo-yo dieting has a definite affect on food preferences, increasing the craving for fat. Fat is the most concentrated source of calories in the diet, and the body appears to store calories from fat more easily than surplus calories from carbohydrates or protein.
3. Repeated cycles of loss and gain take a psychological toll. Many dieters perceive each unsuccessful attempt to keep
weight off as a personal failure. The result, over time, is erosion of self-esteem coupled with depression and even guilt.
4. People who repeatedly lose and regain weight are weakening their immune systems. Women who have tried losing weight more than five times will have about a third lower natural-killer-cell function. In contrast, women who maintain the same weight for five or more years have 40 percent greater natural-killer-cell activity as compared to those whose weight had remained stable for fewer than two years.
5. Some studies suggest that weight cycling may increase the risk for certain health problems. These include high blood pressure, high cholesterol, and gallbladder disease.