Evidence summary

BMI may in some cases not appropriately estimate body fat %, which often means this should be measured separately[1]. Higher body fat % may be indicative of higher cardiovascular risk despite normal BMI[2].

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[3] 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[4].

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))[5]. 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

Conclusion

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 %..

References

1. Powell-Wiley TM, Poirier P, Burke LE, Després J-P, Gordon-Larsen P, Lavie CJ, et al. Obesity and Cardiovascular Disease: A Scientific Statement From the American Heart Association. Circulation. 2021 May;143(21):e984–1010.
2. Chen G-C, Arthur R, Iyengar NM, Kamensky V, Xue X, Wassertheil-Smoller S, et al. Association between regional body fat and cardiovascular disease risk among postmenopausal women with normal body mass index. Eur Heart J. 2019 Sep;40(34):2849–55.
3. O’Donoghue G, Blake C, Cunningham C, Lennon O, Perrotta C. What exercise prescription is optimal to improve body composition and cardiorespiratory fitness in adults living with obesity? A network meta-analysis. Obes Rev an Off J Int Assoc Study Obes. 2021 Feb;22(2):e13137.
4. Schwingshackl L, Dias S, Hoffmann G. Impact of long-term lifestyle programmes on weight loss and cardiovascular risk factors in overweight/obese participants: a systematic review and network meta-analysis. Syst Rev. 2014 Oct;3:130.
5. Kim K-B, Kim K, Kim C, Kang S-J, Kim HJ, Yoon S, et al. Effects of Exercise on the Body Composition and Lipid Profile of Individuals with Obesity: A Systematic Review and Meta-Analysis. J Obes Metab Syndr. 2019 Dec;28(4):278–94.
6. Hsu K-J, Liao C-D, Tsai M-W, Chen C-N. Effects of Exercise and Nutritional Intervention on Body Composition, Metabolic Health, and Physical Performance in Adults with Sarcopenic Obesity: A Meta-Analysis. Nutrients. 2019 Sep;11(9).