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 phar-macotherapy. 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
Evidence Statement: Weight loss produced by lifestyle modifications, reduces blood glucose levels in overweight and obese persons without type 2 diabetes, and reduces blood glucose levels and HbAic in some patients with type 2 diabetes. Evidence Category A.
Rationale: Nine RCTs examined lifestyle therapy. 70, 362, 367 369 373, 403 404 412, 413 Five RCTs among normo-glycemic overweight individuals examined the effects of behavior therapy or lifestyle change on weight loss. Changes in fasting glucose or fasting insulin are used as secondary outcome measures. Improvements in the levels of fasting insulin with weight loss ranged from 18 to 30 percent. While weight loss was maintained, improvements were observed for fasting glucose, fasting insulin, and glucose and insulin levels during oral glucose tolerance testing compared to controls. 367 373 403- 412
Three RCTs of lifestyle modifications were conducted among overweight diabetic patients. 362404413 One RCT of diet and physical activity in African-Americans aged 55 to 79 years with type 2 diabetes showed a 2.4 kg (5.3 lb) weight loss at 6 months compared to the usual-care control group. The intervention group also decreased HbA1c by 2.4 percentage units at 6 months. 362 In another study, weight loss of 5 kg (11 lb) through diet resulted in a reduction of HbA1c by 2 percentage units at 6 months compared with the controls. 413 At 1 year, the difference in weight loss between the two groups was reduced, and diabetic control was similar in each group. In the third study, weight loss, through physical activity in 25 type 2 diabetes patients randomly
* 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.
assigned to physical activity (13 patients) or control (12 patients) groups, was associated with improved HbA1c. 404
One RCT of 530 individuals in China with impaired glucose tolerance compared the effects of diet, physical activity, and diet plus physical activity on the incidence of diabetes. The data were analyzed for the group as a whole and for the lean and overweight groups separately. The overweight individuals in the diet and diet plus physical activity groups lowered their BMIs, while the lean individuals did not. After 6 years, the cumulative incidence rates of diabetes were significantly lower in all three intervention groups than they were in the controls (43.8 percent in the diet group, 41.1 percent in the physical activity group, 46 percent in the diet plus physical activity group, and 67.7 percent in the controls). This was true also if only the overweight persons were included in the analysis. 70
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