Comparative Effects and Dose–Response Relationships of Exercise Modalities on Resting Circulating Interleukin-6 in People with Overweight or Obesity: A Systematic Review and Dose–Response Network Meta-Analysis

Background/Objectives: Exercise may alter resting circulating interleukin-6 (IL-6) in people with overweight or obesity, but comparative effects and dose relationships remain uncertain. Methods: Five databases were searched from inception to 1 March 2026. A frequentist multivariate random-effects network model estimated Hedges g for between-arm differences in IL-6 change using a common within-study pooled change-score SD. Shared-arm sampling covariance and correlated random effects were modeled explicitly. Positive values indicated greater IL-6 reduction. Adult-only exploratory dose models used assigned MET-min/week. Results: The final network comprised 38 randomized reports, 91 arms, with retained arm sample sizes summing to 1518. AE versus control was 0.70 (0.32 to 1.07); CE was 0.36 (−0.11 to 0.82); HIIT was 0.42 (−0.20 to 1.03); and RT was −0.19 (−0.76 to 0.37) (95% confidence intervals). AE versus CE was 0.34 (95% CI −0.19 to 0.87). Heterogeneity was substantial (τ = 0.826; τ2 = 0.683), and all prediction intervals included no effect. Adult dose models favored linear functions; no stable interior optimum or effective-dose threshold was supported. Conclusions: AE had the clearest average estimate versus control, while CE, HIIT, and RT remained uncertain. The evidence was of low or very low certainty. Across-trial dose associations do not establish a causal exercise prescription. Inconsistent reporting of sampling conditions and adherence further limits interpretation.