A representative sample (n=2140) of the Israeli Jewish population aged 40–70 (excluding known diabetic patients), whose body mass index had been measured 10 years earlier, underwent an oral glucose tolerance test and redetermination of body mass index. Irrespective of weight changes, high concurrent and high past body mass index values (≥ 27) were associated with similarly increased rates of glucose intolerance as compared with body mass index values < 27 at both time-points (rate ratio 1.76, 90% confidence limits 1.56–1.99). Glucose intolerance here includes borderline and impaired tolerance as well as Type 2 diabetes. The rate of Type 2 diabetes increased only with increasing past body mass index, while concurrent body mass index had no effect [rate ratios: 2.36 (1.48–3.75) and 1.99 (1.48–2.68) respectively for the medium-(23–26.9) versus-low (<23) and high- (≥ 27) versus-medium past body-mass-index categories]. Weight reduction was associated with only slightly reduced rate of glucose intolerance and had no effect on the rate of diabetes. Mean sum insulin (summed 1 and 2 h levels, mU/l) increased significantly with increasing concurrent body mass index (123, 150 and 190 in the low, medium and high categories) with no effect of past body mass index. It also increased significantly (p < 0.001) in all concurrent body mass index categories from normal tolerance through borderline to impaired tolerance, and decreased significantly (p < 0.001) in diabetes relative to impaired tolerance, although it remained above normal. Means of sum insulin within each glucose tolerance level were similar in the two lower concurrent body mass index categories, with markedly higher (p < 0.001) levels in the high body mass index category. All these findings held after accounting for age, sex, ethnic group and use of antihypertensive medications. We conclude that body mass index ≥ 27 leads to early impairment in glucose tolerance. A prolonged period of obesity is apparently required for the development of Type 2 diabetes and its associated reduced insulin response. The reversibility of the deterioration of glucose tolerance seems to be limited.
Prevalence of Type 2 diabetes prevalence of glucose intolerance past and concurrent overweight insulin response hyperinsulinaemia