Impaired Glucose Tolerance and Diabetes

Forty-nine articles on RCTs were reviewed to evaluate the effect of weight loss on fasting blood glucose and fasting insulin (70, 362, 367, 369, 373, 386, 387, 390-393, 403, 404, 408, 412-415, 439, 440, 446, 470, 473, 474, 482, 485, 490, 492, 493, 576, 676-678, 681, 683, 684, 689, 690, 693, 694, 696-698, 700-702, 708, 709, 712).

Studies were conducted in individuals with normal blood glucose levels (fasting plasma glucose <115 mg/dL [ <6.4 mmol/L]) (367, 373, 386, 387, 390-393, 403, 412, 415, 677, 678, 681, 683, 684, 689, 690, 694, 696-698, 700) 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 to 11.1 mmol/L]) (70, 369), or in individuals with diabetes (fasting plasma glucose of >140 mg/dL or 2 hours postprandial plasma blood glucose 200mg/dL) (362, 404, 408, 413, 414, 439, 440, 446, 470, 473, 474, 482, 485, 490, 492, 493, 576, 676, 693, 701, 702, 708, 709, 712*).

Lifestyle Trials

Of the 38 trials reviewed on the role of lifestyle in weight loss and subsequent changes in blood glucose levels, 16 were on diet alone (70, 373, 412, 413, 415, 439, 440, 576, 677, 683, 689, 693, 701, 702, 708, 709), 8 dealt with physical activity alone (70, 369, 404. 474, 676, 678, 690, 700), 8 focused on diet plus physical activity (70, 362, 403, 446, 470, 473, 681, 684), and 5 examined the role of behavior therapy (367, 482, 485, 490, 493).  One study included diet, behavior therapy, and physical activity (694).  One study (414) included diet, behavioral therapy, and drug therapy. Of the 38 trials, 9 were accepted, and 29 were not considered for these reasons:

• There was a control group that had a weight loss intervention or there was no difference in weight loss between the treatment and control groups (439, 446, 470, 473, 474, 482, 485, 490, 492, 493, 576, 676-678, 683, 684, 690, 693, 694, 701, 702, 708, 709);
• The dropout rate was more than 35 percent (415);
• The results were not reported according to randomized treatment assignments (681);
• Outcome measures were not reported separately for the obese and nonobese people who lost weight (440);
• There was no appropriate control group (700); or
• The population was not overweight (689, 690).

*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. 

Pharmacotherapy Trials

Of the 12 pharmacotherapy trials reviewed, 8 were accepted and 4 were excluded for these reasons:

• The main outcome of the treatment was not weight loss (698); or
• The drug used is not currently being recommended for weight loss (696-698, 712).