A systematic review 1 included randomized controlled trials with at least 1-year duration and involving adult participants with BMI at least 28. The effects of low-energy diet (energy deficit 600 kcal/day or low-fat diet) and physical exercise on weight were compared with controls receiving no active therapy. Three trials with a total of 774 subjects were included. At 12 months from randomization, the weighted mean difference (WMD) between the groups was 3.4 kg (95% confidence interval [CI] -4.2 to -2.6) and at 24 months -2.7 kg (95% CI -3.6 to -1.8), respectively. In another analysis of the same review 2 exercise and diet was compared to diet alone. Five RCTs were found with a total of 269 subjects. In two trials, WMD at 12 months was -2.0 kg (95% CI -3.2 to -0.7).
Another systematic review was based on literature search in the years 1997 to 2001. Randomized controlled trials with at least 1-year duration were included. In total 15 trials comparing physical exercise and diet to diet alone were found. In some of the trials the subjects had either coronary heart disease, decreased glucose tolerance or hypertension. In the combined therapy group the change in weight at 1 year was on average -7.5 kg (range -15.2 to -4.2). The respective change in the control group was +0.3 kg (-0.9 to 1.7), so the net change was -6.4 kg (-10.4 to -3.4). In trials with duration over 1 year the change in the combination therapy group was -3.1 kg (-9.9 to 0) and in the control group 0.5 kg (-2.7 to 3.0).
Comment: In the recent meta-analyses 1 2 3 the results (i.e., no clear difference in the reduction of overweight between combined diet and exercise therapy compared to diet alone) are thus not significantly different from those reported in earlier analyses: similar results were found in the systematic review by Wing 4 and in meta-analyses by Miller et al 5 and Ballor et al 6. The meagre results have been explained with different factors in the study design and conduct, such as short duration of interventions, different compensation mechanisms (physical activity in other contexts, e.g. in the everyday activities, is reduced but the interventional exercise program is carried out), and the possible ”interaction” between the energy restriction in the diet and the physical exercise (the less energy is obtained from nutrition, the less "possibility" is left for exercising). There are still only few longer-term trials, with duration over 1 year, and the drop-out rates in these trials have been rather high.
The quality of evidence is downgraded by limitations in study quality.
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