TTM-based interventions significantly reduce BMI and waist circumference in individuals with overweight or obesityTTM Based Interventions Show Potential for Weight Loss

Globally, an estimated 2.2 billion adults and 430 million children and adolescents are affected by overweight or obesity. Interventions based on the transtheoretical model (TTM) have demonstrated efficacy in modifying dietary behaviors, reducing body mass index (BMI), and improving other health outcomes in overweight or obese populations. However, the magnitude of these effects varies across studies and study designs. This study aimed to systematically evaluate the impact of TTM-based interventions on BMI and other physical health indicators among individuals with overweight or obesity, with separate analyses for randomized controlled trials (RCTs) and one-group repeated measures designs (ORMDs). A systematic review was conducted following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, searching six databases—CNKI, PubMed, Web of Science, Cochrane Library, EBSCO, and Scopus—from their inception through March 30, 2025. Studies were eligible if they employed TTM-based interventions and reported BMI outcomes in overweight or obese populations. Hedges’ g served as the effect size measure. For ORMDs, sensitivity analyses were conducted using pre-post correlation coefficients of r = 0.3, 0.5, and 0.7. Random-effects meta-analyses (REML estimator) were performed separately for RCTs and ORMDs. Subgroup analyses and meta-regression were conducted for BMI outcomes to explore sources of heterogeneity. Publication bias was assessed using funnel plots and Egger’s test, and sensitivity was evaluated using leave-one-out analyses. A total of 20 studies (1,736 participants) were included, comprising 9 RCTs and 11 ORMDs. Among ORMDs, TTM-based interventions significantly reduced BMI [k = 11, g = −0.467, 95% CI (−0.763, −0.171), p = 0.002, I2 = 86.6%], body weight [k = 5, g = −0.323, 95% CI (−0.563, −0.084), p = 0.008, I2 = 78.9%], and waist circumference [k = 2, g = −0.375, 95% CI (−0.542, −0.209), p  TTM-based interventions showed significant improvements in BMI, body weight, waist circumference, and self-efficacy when evaluated using ORMDs, with effects robust to assumptions about pre-post correlation. However, these improvements were not statistically significant under the more conservative between-group comparisons of RCTs. The discrepancy highlights the importance of study design in evaluating behavioral interventions. ORMDs may capture within-person change that RCT between-group contrasts fail to detect, but are also susceptible to expectancy and maturation effects. Future research should prioritize well-controlled RCTs with adequate blinding and intention-to-treat analyses, and interventions combining nutritional education with exercise are recommended for optimal BMI reduction.