16 Systematic reviews and meta-analyses were identified that evaluated the effect of physical activity on weight and BMI in patients with BMI >25 [1-14]. The studies included in these articles are heterogenous in key aspects such as exercise interventions and mean BMI of the study population. Nevertheless, exercise at moderate to high intensity on its own appears to have a small to moderate effect on weight.
A network meta-analysis of 45 studies with 3566 participants with an age range of 18-65 and BMI over 30 investigated the effect of exercise interventions that were longer than 8 weeks . The effect of exercise on body weight was found to be small, with mean values ranging from −0.05 to −1.01 kg, with interventions that combined vigorous aerobic exercise with high-load resistance training the most effective (−1.01 kg (−2.71, −0.40)). BMI was reduced significantly as well in this group (-2.79 kg m−2 [CI = −5.95, −0.36]). Resistance training alone was not effective. This was supported by several other meta-analyses with similar results [4,12,16].
A meta-analysis with an average participation in the exercise interventions of 22 weeks, 4 times per week for ~50 min at moderate to vigorous intensity, showed statistical significant reduction of weight in the 9 trials looking at overweight and obese individuals (d = −0.63 SMD (95% confidence interval (CI), −0.89–−0.36; p < 0.001; k = 9)) compared to overweight and obese individuals who did not participate in the exercise interventions . Similar results were found in the 7 trials looked at for BMI (d = −0.50 SMD (95% CI, −0.78–−0.21; p < 0.001; k = 7)). Furthermore, Hsu et al demonstrated a reduction in body weight as a result of at least moderate intensity exercise (MD = −4.3 kg, 95% CI: −7.61, −0.99, p = 0.01; I2 = 0%) and BMI (MD = −1.98 kg/m2, 95% CI: −3.29, −0.67, p = 0.003, I2 = 0%) in a meta-analysis 7 studies of patients with sarcopenic obesity(12). Kim et al found a medium to large effect on exercise interventions on BMI (standardized mean difference [SMD], 0.533), with exercise duration (weeks of exercise) and intensity being the best correlators with improvement in obesity 
A systematic review of 6 studies on older individuals (65+) did not find any significant differences in weight loss following exercise programmes of at least 6 months, but intensity was not detailed .
Diet plays an important role in weight loss and may have a synergistic role with exercise. In a meta-analysis of 22 trials with a mean age of 35-70 and BMI of 25.6 and 38.2 kg/m2, where 3521 participants trained for at least 12 months at 50-85% their maximal heart rate, the addition of exercise to dieting resulted in a significantly more pronounced reduction in body weight [mean differences (MD): -1.38 kg, 95% confidence interval (CI) -1.98 to -0.79] .
Diet together with exercise appears to be more effective in inducing body compositional changes than either exercise or diet alone . The highest level of successful weight loss and weight maintenance programmes incorporated physical activity in a summary of 48 studies, including 30 RCTs .
Quality of evidence
A: Consistent evidence from meta-analysis and systematic review
Strength of recommendation
1 – Small, but significant benefit, low risk of physical activity
Exercise has a small but favourable effect on weight loss and BMI and works in synergy with diet in patients who are overweight or obese. A combination of high-intensity aerobic and high-load resistance training may be the most effective in reducing weight and/or BMI. The effect amongst older individuals is less clear. Duration of exercise programme and intensity appear to be the most important modulators of success.
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