News release

From: International Congress on Obesity 2026

A new systematic review and meta-analysis presented at this year’s International Congress on Obesity (ICO2026) hosted by the World Obesity Federation (WOF) in Mexico City, Mexico (15-17 July) is the first study to show that behavioural weight loss interventions reduce the risk of obesity-related cancers in people living with overweight and obesity – by 15%. The study is by Dr Matthew Harris and Professor Andrew Renehan, Manchester Cancer Research Centre, University of Manchester, UK.

Excess body fat, commonly estimated by body mass index (BMI), is a major modifiable risk factor causally associated with the increased incidence of at least 13 cancer types, including most commonly colorectal, post-menopausal breast, endometrial, oesophageal adenocarcinoma and kidney, known collectively as obesity-related cancers (ORCs).

Previous reviews of behavioural weight loss interventions and cancer risk were inconclusive, mainly due to small sized studies with short follow-up. In this new study, the authors conducted a systematic review and meta-analysis of clinical trials to evaluate whether behavioural weight loss interventions (diet and exercise) reduce cancer risk.

They searched PubMed, Embase, Web of Science, and CENTRAL (entries to August 2025) to identify randomised controlled trials (RCTs), with follow-up of at least 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. Statistical modelling was used to estimate the relationships.

The analysis 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 at least 24 months of follow-up.

Behavioural interventions were associated with no statistically significant effect on total cancer incidence, but in seven RCTs studies reporting ORCs (8,417 participants; 589 cancers), diet and exercise for weight loss was associated with a 15% lower obesity-related cancer risk. Statistical analysis showed a 98% probability that diet and exercise led weight loss reduces obesity-related cancer risk in these studies.

The authors conclude: “This study is the first to show that behavioural weight loss intervention reduces the incidence of obesity-related cancer in people living with overweight and obesity. However, this evidence is limited due to high-risk of biases, and variety 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.

“This study add further support to the notion that weight loss from all forms of obesity treatment can reduce obesity-related cancer risk however further studies are required to prove this.”

He adds his team at the University of Manchester, as well as consortia they are involved in, are planning to explore such trials.