BMI may in some cases not appropriately estimate body fat %, which often means this should be measured separately. Higher body fat % may be indicative of higher cardiovascular risk despite normal BMI.
A network meta-analysis of 45 studies from 6 continents with 3566 participants, of which 76% were female, with an age range of 18-65 and BMI over 30 found small to moderate effects of exercise on body fat. Exercise interventions were compared to no exercise and lasted longer than 8 weeks. The exercise intervention with the highest likelihood (P score = 0.80) of decreasing %BF was a combination of high‐intensity aerobic and high‐load resistance training (−2.82% [CI = −5.50, −0.14]).
A network meta-analysis of 22 trials of over 12 months in duration and age range of 35-70 showed that the mean difference in fat mass [MD: -1.65 kg (95% CI -2.81 to -0.49), I2 = 61%] was more pronounced with a combined diet and exercise intervention compared to dietary intervention alone. There were 3521 participants, of which 680 also had Type 2 Diabetes with a BMI ranged between 25.6 and 38.2kg/m2. Exercise prescription was partly supervised and included aerobic exercise (i.e. jogging, walking, flexibility, circuit training) and resistance training, overall 50%–85% of maximal heart rate. When directly comparing diet to exercise however, the reduction in fat mass was more pronounced for diet [MD: -2.20 kg (95% CI -3.75 to -0.66), I2 = 82%]. The improvements in body measures were more pronounced in younger individuals.
A meta-analysis of 64 articles with an exercise intervention time of 16.5 weeks and average time of 153.3 minutes per week of different intensity found a below medium effect size of exercise on body fat % in the 22 studies that did not include a dietary intervention (0.464 (0.273 to 0.655)). The effect size was higher in moderate and vigorous intensity exercise compared to low intensity as well as increasing with increasing time of exercise in a dose-response manner.
Hsu et al looked at 15 studies with an age range of 41-90 and 739 participants with sarcopenia, finding that exercise decreased body fat mass (MD = −2.99 kg, 95% CI: −4.39, −1.59, p < 0.0001, I2 = 0%), and BF% (MD = −2.31%, 95% CI: −3.26, −1.36, p = 0.00001, I2 = 0%)(6). Exercise interventions lasted between 8-24 weeks and compared exercise protocols of aerobic, resistance or combined with control (no exercise intervention).
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 favourable effect on body fat and works in synergy with diet in patients who are overweight or obese. A combination of high-intensity aerobic and high-load resistance training appears to be the most effective in reducing body fat %..
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