Forty-nine articles of RCTs were reviewed to evaluate the effect of weight loss on fasting blood glucose and fasting insulin. Studies were conducted in individuals with normal blood glucose levels (fasting plasma glucose < 115 mg/dL [< 6.4 mmol/L]), in individuals with impaired glucose tolerance (fasting plasma glucose of <140 mg/dL [7.8 mmol/L] or 2 hours postprandial plasma glucose of 140 to 200 mg/dL [7.8-11.1 mmol/L]), or in individuals with diabetes (fasting plasma glucose of 140 mg/dL or < 2 hours postprandial plasma blood glucose 200 mg/dL).*
The methods of weight loss included diet, physical activity, or both; behavior therapy; and pharmacotherapy. The dietary interventions included low calorie and very low calorie, and those that promoted changes in diet composition, such as amount and type of dietary fat. Physical activity varied from controlled individualized exercise programs to informal group sessions coupled with behavior therapy and dietary changes. The degree of blinding of outcome measures was not always well described, nor was there a systematic consideration of concurrent effects of changes in medication or adherence to medication among diabetic patients enrolled in these weight reduction studies.
Of the 17 RCT articles considered acceptable, 10 included normoglycemic individuals (367, 373, 386, 387, 390-393, 403, 412), 2 included patients with impaired glucose tolerance (70, 369), and 5 included patients with type 2 diabetes (362, 404, 408, 413, 414).
* The reviewed articles used the old definitions of the American Diabetes Association (ADA) for impaired glucose tolerance and diabetes. As of November 1997, the new ADA definitions define impaired fasting glucose as those individuals having a fasting plasma glucose of 110 to 125 mg/dL, and diabetes as those individuals having a fasting plasma glucose of 126 mg/dL or 2 hours postprandial plasma glucose of 200 mg/dL.