Obesity and cancer: new research reveals gaps in our understanding
Two separate studies have highlighted the impacts that obesity can have on cancer prevalence, revealing that more than half of cancer patients in England had a history of obesity and that excess weight is a key driver behind rising cancer rates in younger adults.
Excess weight is the strongest clue to rise in cancer rates in under 50s – but doesn’t tell the whole story
A study from The Institute of Cancer Research and Imperial College London (both UK) has identified excess weight as a key contributor to rising cancer rates among under 50’s, but found that increased BMI alone cannot explain the full rise.
Published in BMJ Oncology, the research examined national cancer registry data from 2001–2019 across 22 cancer types in women and 21 in men. The analysis identified 11 cancers increasing among younger adults aged 20–49 that are linked to known behavioral risk factors, all but one (oral cancer), are known to be associated with excess weight.
Critically, while rates of several cancers have been increasing in younger adults over the past two decades, most established behavioral risk factors—including smoking, alcohol use, red or processed meat consumption, low fiber intake and physical inactivity—remained stable or declined in England during this period, making these factors unlikely to substantially explain the increase.
In contrast, overweight and obesity have increased steadily since 1995, with the largest increases seen in younger women, a 2.6% relative increase per year since 1995.
However, the researchers found that BMI increases alone are insufficient to account for the overall rise. For example, bowel cancer rates in younger women linked to BMI rose from 0.9 to 1.6 per 100,000 people, but rates not attributable to BMI rose from 6.4 to 9.6 per 100,000 people, suggesting that additional factors are at play.
“Our findings show that while cancer rates are rising in younger adults, the trends are unlikely to be explained by changes in most known behavioral risk factors,” explained study author Montserrat García‑Closas from The Institute of Cancer Research. “Excess weight is an important contributor, although it cannot fully account for the scale of the rise in bowel and other cancers. This tells us that multiple factors—including early‑life exposures—may be acting together.”
Single BMI measurement at cancer treatment initiation doesn’t capture full story
A separate, real-world study, of more than 79,000 patients across 13 cancer types, has demonstrated that relying on a single BMI measurement at the start of cancer treatment start may greatly underestimate patients’ lifetime exposure to obesity.
The results emphasize the need to consider lifetime obesity exposure in clinical decision-making. This is particularly important for patients receiving chemotherapy as body weight can inform dosing.
The research, funded by World Cancer Research Fund and led by the University of Oxford (UK), found that lifetime obesity prevalence exceeded 50% in every one of the 13 cancer types studied.
Pancreatic cancer showed the most dramatic difference: only 13.7% of patients had obesity at treatment start, yet 55.8% had experienced obesity at some point in their lives, demonstrating that current weight doesn’t provide a complete picture of someone’s health history.
“This work highlights the limitations of using a single BMI measurement, which fails to accurately reflect past obesity exposure,” explained study lead Simon Lord (University of Oxford). “How obesity affects cancer prognosis is extremely complex, with both current and previous obesity likely to be important.”
The authors suggest using longitudinal BMI measurements to accurately classify obesity exposure in cancer patients receiving systemic therapy.
Implications for clinical care and public health
Both studies underscore the complexity of obesity’s role in cancer and highlight important implications for clinical practice and prevention strategies.
“…We cannot wait to act,” García‑Closas added. “Tackling obesity across all ages, particularly in children and young people, through stronger public health policies and wider access to effective interventions, could slow the rise in cancer and prevent many cancers—and must become a national priority.”
Obesity is a risk factor for 13 cancer types, and global projections suggest that over 2 million cancer cases could be attributable to obesity by 2070. With established lifestyle risk factors for cancer either stable or improving in the UK, understanding the full picture of obesity’s impact is critical in tackling cancer.
Sources: www.wcrf.org/about-us/news-and-blogs/history-of-obesity-and-cancer/; www.icr.ac.uk/about-us/icr-news/detail/excess-weight-is-the-strongest-clue-to-the-rise-in-cancer-rates-in-under-50s—but-doesn’t-tell-the-whole-story