To determine if weight loss may prevent conversion of impaired glucose tolerance (IGT) to diabetes, because weight loss reduces insulin resistance. The prevalence of IGT in the U. S. population is estimated at 11.2%, more than twice that of diabetes. Furthermore, because an oral glucose tolerance test is needed for its detection, most of these patients are undiagnosed. Screening for IGT would be meaningful if progression to diabetes could be delayed or prevented.


For an average of 5.8 years (range 2–10 years), 136 individuals with IGT and clinically severe obesity (>45 kg excess body weight) were followed. The experimental group included 109 patients with IGT who underwent bariatric surgery for weight loss. The control group was made up of 27 subjects with IGT who did not have bariatric surgery. The criteria of the World Health Organization was used to detect IGT and diabetes in this population. The main outcome measure of this nonrandomized control trial is the incidence density, or number of events (development of diabetes) divided by the time of exposure to risk.


Of the 27 subjects in the control group, 6 developed diabetes during an average of 4.8 ± 2.5 years of postdiagnosis follow-up, yielding a rate of conversion to diabetes of 4.72 cases per 100 person-years. The 109 individuals of the experimental group were followed for an average of 6.2 ± 2.5 years postbariatric surgery. Based on the 95% confidence interval of the comparison group, we would expect to find that between 22 and 36 subjects in the experimental group developed diabetes over the follow-up period. Only 1 of the 109 experimental-group patients developed diabetes, resulting in a conversion rate of the experimental group of only 0.15 cases per 100 person-years, which is significantly lower (P < 0.0001) than the control group.


Weight loss in patients with clinically severe obesity prevents the progression of IGT to diabetes by >30-fold.

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