It is surprising that debate continues about the effectiveness of dietary treatments for obesity. Perhaps this is partly related to ambiguity in the term effectiveness. It is well known that most treatments produce temporary weight loss. But it is equally well known that 90% to 95% of those who lose weight regain it within several years.1 This poor outcome has led to charges that traditional treatments for obesity should be abandoned and countercharges that it is irresponsible to withhold treatment for such a serious problem. The failure of reducing diets to produce lasting improvement was recently reiterated at a National Institutes of Health consensus conference, which also warned about the adverse effects of treatment.2

The failure of fat people to achieve a goal they seem to want - and to want almost above all else - must now be admitted for what it is: a failure not of those people but of the methods of treatment that are used. It is no longer a mystery why diets have such a poor long term record of success. Indeed the failure of obese people to become or remain thin by “normalising” their food intake follows logically from studies on the heritability of obesity,3 the biology of weight regulation,4 and the physiology of energy metabolism.5