Introduces a metabolic approach to the effects of obesity on glucose metabolism. Highlights the frequent progressive development of impaired glucose tolerance and diabetes. Demonstrates continuity in both cross-over and longitudinal studies. The reversibility of the phenomena, as well as prevention and therapy, are also presented in relation to physiopathological observations. Cites epidemiological studies which relate the progressive occurrence of diabetes to obesity in populations where the lifestyle has changed with richer food and decreased exercise.