Effects of conjugated linoleic acid and exercise on body composition and obesity: a systematic review and meta-analysis

Conjugated linoleic acid (CLA) has been reported to have anti-obesity and antidiabetic effects. However, the benefits of CLA combined with exercise remain unclear, and studies report conflicting results.A systematic review and meta-analysis were performed to investigate the synergistic effect of CLA and exercise on body composition, exercise-related indices, insulin resistance, and lipid profiles; and of the safety of CLA supplements.In October 2021, the PubMed, Embase, and Cochrane Library databases were searched for reports on clinical trials of the combined intervention of CLA and exercise.A total of 18 randomized controlled trials and 2 crossover trials were included. The methodological quality assessment was performed using the revised Cochrane risk-of-bias tool. Pooled effect sizes were reported as standardized mean difference (SMD) for continuous data and risk ratio for dichotomous data with their corresponding 95% confidence intervals (CIs). Heterogeneity was tested using the I2 statistic.The combination of CLA and exercise resulted in significantly decreased body fat (SMD, -0.42 [95%CI, -0.70, -0.14]; P = 0.003; I2 = 65) and insulin resistance (SMD, -0.25 [95%CI, -0.44, -0.06]; P = 0.01; I2 = 0) than did exercise alone. In subgroup analysis, the following factors were associated with significant outcomes: (1) body mass index ≥25 kg/m2; (2) female sex; (3) follow-up time >4 weeks; and (4) intervention duration >4 weeks. Nevertheless, supplementation with CLA during exercise programs was not effective for body-weight control, exercise performance enhancement, or lipid-profile improvement. CLA in combination with exercise did not result in a higher risk of adverse events (risk ratio, 1.32 [95%CI, 0.94-1.84]; P > 0.05; I2 = 0).CLA combined with exercise is generally safe and can lower body fat and insulin resistance but does not reduce body weight, enhance exercise performance, or improve lipid profiles.