A Cochrane review included 18 studies with a total of 1 467 subjects. Dietary approaches included low-fat/high-carbohydrate diets, high-fat/low-carbohydrate diets, low-calorie (1000 kcal per day) and very-low-calorie (500 kcal per day) diets and modified fat diets. Dietary advice plus exercise as compared with dietary advice alone (6 trials, n=340), was associated with a statistically significant mean decrease in glycated haemoglobin at 6 months (pooled weighted mean difference, WMD 0.9%, 95% confidence interval 0.4 to 1.3) and at twelve months (WMD 1.0%, 95% CI 0.4 to 1.5). However, all studies were at high risk of bias. No data were found on micro- or macrovascular diabetic complications, mortality or quality of life.
A systematic review including 14 controlled clinical trials with a total of 504 subjects (11 RCTs, n=412) was abstracted in DARE. Exercise significantly lowered HbA1c compared with no exercise. HbA1c was 7.65% in the exercise group and 8.31% in the control group (WMD –0.66%, 95% CI –0.98 to –0.34; 8 RCTs, 1 non-RCT, n=310). Exercise plus diet significantly lowered HbA1c compared with no exercise plus no diet (WMD –0.76%, 95% CI –1.32 to –0.20; 2 RCTs, n=142). Similar results were found for aerobic exercise compared with resistance training. There was no significant difference in body mass between exercise and no exercise (WMD 0.06%, 95% CI –0.15 to +0.26; 8 RCTs, 3 non-RCTs, n=368) nor between exercise plus diet and no exercise or diet (WMD –0.20%, 95% CI –0.54 to +0.14; 2 RCTs, n=142).
Another meta-analysis assessing associations of structured exercise training in type 2 diabetes included 47 RCTs with 8538 patients. Structured exercise decreased HbA1c (-0.67%, 95% CI -0.84% to -0.49%; 23 trials) compared with control. Declines in HbA1c compared with control were -0.73% (95% CI -1.06% to -0.40%) in structured aerobic exercise; -0.57% (95% CI -1.14% to -0.01%) in structured resistance training; and -0.51% (95% CI -0.79% to -0.23%) in both combined. Structured exercise durations of more than 150 minutes per week were associated with HbA1c reductions of 0.89%, while structured exercise durations of 150 minutes or less per week were associated with HbA1c reductions of 0.36%. Combined physical activity advice and dietary advice was associated with decreased HbA1c (-0.58%; 95% CI -0.74% to -0.43%) as compared with control.
Comment: The quality of evidence is downgraded by limitations in study quality.
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