Is 5% weight loss a satisfactory criterion to define clinically significant weight loss?

The idea of quantitative measurement came to obesity in stages. Quetelet (1) introduced the body mass index (BMI) which was applied nearly a century later to the evaluation of degree of overweight in studies of familial inheritance of obesity. Publication of average weight tables in the 1850s was expanded to “ideal” weight tables by the life insurance industry in the mid-20th century. The relation of increasing weight to risk for many diseases was extended by the Framingham Study from which Gordon and Kannel (2) concluded that if everyone were at optimal weight, the incidence of coronary heart disease would be reduced by 25% and congestive failure and brain infarctions would be reduced by 35%. By 1975 there had been many observations about the association of obesity and a variety of health problems. Yet at this time, there were no generally agreed upon metrics for evaluating health effects of weight loss. In 1973, Dr. Thaddeus Prout (3) authored a final report to the Food and Drug Administration (FDA) Director of Anorectic Drugs which interpreted the statistically significant differences between placebo and anorectic drugs in the short-term clinical trials reviewed by the FDA as being “clinically trivial” (p 501). Bray (4) at the 1973 Fogarty International Center Conference noted: “Little uniformity exists in the criteria which are used for evaluating weight loss or in the uniformity of follow-up between various clinical trials” (p 60). The Fogarty Conference report suggests several criteria, including percent achieving 20and 40-pound weight loss and a weight reduction index. Clearly, in the mid-1970s the obvious question was “What defines clinically significant weight loss?” Up to this point in the story, few, if any, had suggested that modest weight losses might have important health benefits.