Background
Excess adiposity, commonly approximated by body mass index (BMI), is a major modifiable risk factor causally associated with the increased incidence of at least 13 cancer types, known as obesity-related cancers (ORCs). Previous reviews and meta-analyses of behavioural weight loss interventions and cancer risk were inconclusive, mainly due to available studies being of small size with short follow-up.

Objective
We conducted a systematic review and meta-analysis to evaluate whether behavioural weight loss interventions reduce cancer risk.

Methods
We searched PubMed, Embase, Web of Science, and CENTRAL (inceptions to August 2025) to identify randomised controlled trials (RCTs), with follow-up ≥12 months, comparing behavioural weight loss interventions for obesity management (dietary, physical activity, or psychotherapy) against a control. The primary outcome was total cancer incidence, sub-divided into ORCs and non-obesity-related cancers. Risk of bias was assessed using a subject-specific ROB-2 tool. We derived pooled risk ratios (RRs) with 95% confidence intervals (CIs) using random effects. Supporting analysis included Bayesian meta-analysis. and univariate meta-regression.

Results
We included 22 RCTs (12,893 participants; 1,157 cancers) varying in participant numbers from 55 to 5145; mean BMIs from 25.2 to 40 kg/m2; and achieving mean percentage weight losses above control from 0.4% to 10.4%. Interventions varied in intensity and delivery; 83% of studies had ≥24 months’ follow-up. 70% (16) of the RCTs were at high-risk of bias. Behavioural interventions were associated with no effect on total cancer incidence (RR 0.94, 95% CI 0.87–1.02) but in 7 RCTs studies reporting ORCs (8,417 participants; 589 cancers), behavioural weight loss intervention was associated with lower cancer risk (RR 0.85, 95% CIs 0.73–0.99). Bayesian meta-analysis supported this finding reporting a 98% posterior probability of a reduction in obesity-related cancer risk in patients undergoing behavioural weight loss intervention. 

Conclusions and implications for practice and policy
This updated meta-analysis is the first to show that behavioural weight loss intervention reduces the incidence of ORCs in people living with overweight and obesity. However, this evidence is limited due to high-risk of biases, and heterogeneity in the intensity and effectiveness of interventions. Given the expansion of pharmacological obesity-management options, these findings reinforce the role of behavioural support as part of holistic, multi-modal obesity-related cancer prevention.

Registration
?PROSPERO CRD42024582375.

Funder
This work is funded by Cancer Research UK through the Manchester Cancer Research Centre Leeds-Manchester Collaboration PhD scheme (SEBCATP-2023/100010).
 

Figure 1. Meta analysis for behavioural weight loss intervention and cancer risk