When Dr. Matthew Harris started looking at whether losing weight through diet and exercise could actually prevent cancer, he expected to find some connection — but not a result this strong. Researchers at the University of Manchester in the United Kingdom have become the first team in the world to show that programs focused on eating better and moving more can lower the risk of obesity-related cancers by 15 percent in people with overweight or obesity.
The findings come from what scientists call a meta-analysis — a study of studies. The team gathered results from 22 separate clinical trials involving 12,893 participants. In those trials, researchers tracked people who joined structured diet and exercise programs and compared their cancer rates to people who did not. The participants lost between 0.4 and 10.4 percent more body weight than people in the control groups.
When the team zoomed in on the seven trials specifically measuring obesity-related cancers — the kinds of cancer linked to carrying extra body fat — the pattern was clear. Among 8,417 participants who developed 589 cancers, those who changed their behavior through diet and exercise showed a 15 percent lower risk. The statistics showed a 98 percent probability that this result was not due to chance.
"This study is the first to show that behavioral weight loss interventions reduce the incidence of obesity-related cancer in people living with overweight and obesity," the authors wrote.
Obesity is linked to at least 13 types of cancer, including colorectal, breast, endometrial, esophageal, and kidney cancers. Doctors commonly measure body fat using body mass index, or BMI — a simple ratio of weight to height. Previous reviews of diet and exercise programs had been inconclusive, largely because earlier studies were small and did not follow people long enough to see meaningful cancer outcomes.
The new research was presented at the International Congress on Obesity 2026 in Mexico City, hosted by the World Obesity Federation. The studies included in the analysis had follow-up periods of at least 12 months, with 83 percent tracking participants for two years or more.
Professor Andrew Renehan, who co-led the study at the Manchester Cancer Research Center, acknowledged that the evidence still has limits. Some trials had quality concerns, and programs varied widely in how intense they were. Still, the researchers say the findings reinforce that helping people lose weight — whether through food choices, physical activity, or counseling — should be part of cancer prevention efforts.
"This study adds further support to the notion that weight loss from all forms of obesity treatment can reduce obesity-related cancer risk," Harris said. His team at the University of Manchester is now planning further studies to dig deeper into the connection — and to explore how weight-loss medications might fit into the picture alongside lifestyle programs.
For everyday people, the takeaway is straightforward: small, sustained changes in what you eat and how much you move may do more than shift the number on a scale. They might also lower your chances of developing cancer down the road.