YO-YO dieting - that vicious cycle of losing five kilograms only to gain back seven - may be frustrating to the dieter, but it does not carry significant health risks, a surprising new report shows. The study contradicts some previous research suggesting that up-and-down dieting could actually be dangerous because it disrupted the body's metabolism. Those findings, which seemed to support the notion that it may be better to remain fat, helped spawn a 'down-with-dieting' movement in US. But now comes a report by a task force of the National Institutes of Health concluding that 'there is no convincing evidence that weight cycling in humans has adverse effects on body composition, energy expenditure, risk factors for cardiovascular disease, or the effectiveness of future efforts at weight loss'. The National Task Force on the Prevention and Treatment of Obesity based its findings on a review of 30 years of published studies, involving both laboratory animals and humans, on the effects of weight cycling. The researchers said that some of those studies do not stand up under closer scrutiny because they did not determine the effects of yo-yo dieting in obese people as opposed to normal-weight individuals, and most did not examine intentional versus unintentional weight loss. The panel, reporting in the Journal of the American Medical Association, said that while more research was needed on the long-term consequences of yo-yo dieting, 'obese individuals should not allow concerns about hazards of weight cycling to deter them from efforts to control their body weight'. Being overweight can put a person at increased risk for heart disease, high blood pressure, diabetes and some types of cancer. But even a moderate weight loss, as little as five kilograms can enhance a person's well-being, the panel said.