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Yo-yo dieting or yo-yo effect, also known as weight cycling, is a term coined by the public health scholar Kelly D. Brownell, in reference to the cyclical loss and gain of weight, resembling the up-down motion of a yo-yo. In this process, the dieter is initially successful in the pursuit of weight loss but is unsuccessful in maintaining the loss long-term and begins to gain the weight back. The dieter then seeks to lose the regained weight, and the cycle begins again.
The reasons for yo-yo dieting are varied but often include embarking upon a hypocaloric diet that was initially too extreme. At first the dieter may experience elation at the thought of weight loss and pride in 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. Ultimately, the dieter reverts to their old eating habits, now with the added emotional effects of failing to lose weight by restrictive diet. Such an emotional state leads many people to eating more than they would have before dieting, causing them to rapidly regain weight.
The process of regaining weight and especially body fat is further promoted by the high metabolic plasticity of skeletal muscle. The Summermatter cycle explains how skeletal muscle persistently reduces energy expenditure during dieting. In addition, food restriction increases physical activity which further supports body weight loss initially. Such weight regain in the form of preferential catch-up-fat is well documented after weight loss due to malnutrition, cancer, septic shock or AIDS and thus constitutes a general phenomenon related to weight loss.
Effects on health
This kind of diet is associated with extreme food deprivation as a substitute for healthy 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 starvation response, leading to rapid weight gain of only fat. This is a cycle that changes the body's fat-to-muscle ratio, one of the more important factors in health. A report by the American Psychological Association reviewed thirty-one diet studies and found that after two years of dieting up to a third of dieters weighed more than they did before they began the diet, another third regained the weight they lost, and the last third kept the lost weight off.
One study in rats showed those made to yo-yo diet were more efficient at gaining weight. However the research compiled by Atkinson et al. (1994) showed that there are “no adverse effects of weight cycling on body composition, resting metabolic rate, body fat distribution, or future successful weight loss”, and that there is not enough evidence to show risk factors for cardiovascular disease being directly dependent on cyclical dieting patterns. A more recent review concluded, "...evidence for an adverse effect of weight cycling appears sparse, if it exists at all."
Since there is "no single definition of weight cycling [that] can be endorsed", it is almost impossible for research to draw specific conclusions about the actual effects of cyclical dieting, until it becomes more definitely defined.
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