Experts identify new link between obesity and 13 types of cancer – and you’re still at risk even if you’ve LOST weight

More than half of cancer patients starting treatment in England have a history of obesity, a landmark study has found.

The precise role it plays in the deadly disease is even greater than feared; previous estimates suggested it could trigger four in ten cases.

Experts from the University of Oxford have found that relying on a single weight measurement when treatment begins can greatly underestimate a patient’s lifetime obesity, altering their chances of survival.

Obesity is linked to at least 13 types of cancer, but experts warn that losing weight is no longer enough.

Dr. from the World Cancer Research Fund. “This research highlights the opportunity to consider patients’ history of obesity as well as their current health when considering wider clinical decision-making,” said Helen Crocker.

‘While the link between obesity and cancer risk is well established, its impact on cancer outcomes remains unclear and relying solely on BMI at the start of treatment may miss important lifetime exposures that may influence cancer prognosis.’

The study, which spanned more than a decade, found that when past obesity was included, prevalence exceeded 50 percent for each of the 13 cancers studied.

Using only a single BMI measurement, only 25 percent of patients were classified as clinically obese.

In pancreatic cancer, only 14 percent of patients were obese at the start of treatment, while 56 percent were obese at some point in their lives; This shows that current weight does not provide a complete picture of a person’s health.

Findings – published in the journal ESMO Real World Data and Digital Oncology – Experts said they emphasized the need to combat obesity directly, rather than treating it later.

The team, led by Professor Simon Lord, an expert in cancer treatment, found that previous excess weight can significantly affect treatment success.

They analyzed historical BMI data obtained from digital health records of 79,271 patients receiving systemic therapy; These treatments include any treatment in which drugs circulate in the bloodstream, such as chemotherapy.

The results showed that obesity rates varied by cancer type; What often manifests as unexplained weight loss and loss of appetite was linked to lower rates of obesity in initial treatment.

These included pancreatic, gastroesophageal, bowel and lung cancer, as well as non-Hodgkin’s lymphoma, which affects infection-fighting white blood cells.

Obesity was more common at the beginning of treatment for uterine cancer, breast cancer, and malignant melanoma, a type of skin cancer that can spread to other parts of the body.

Further analysis showed that older patients who were aged 75 or over when they started treatment had lower rates of obesity, while those living in more deprived areas were more likely to be obese.

Scientists believe that obesity may increase cancer risk through biological mechanisms such as chronic inflammation, changes in metabolism, and changes in hormone levels.

Decreased participation in cancer screening programs and reduced effectiveness of screening procedures in people living with obesity (which are more likely to be areas of deprivation) may also be factors.

The researchers concluded: ‘Our findings have important implications for understanding the relationship between obesity and cancer outcomes, particularly for precision medicine.

‘This study provides a clear rationale for considering both current and historical BMI in clinical decision-making and outcome research.

‘Failing to do this risks missing an important part of the clinical picture.’

Senior research fellow in the university’s oncology department, Dr. Victoria Perletta added: ‘Our study may have implications for clinical decision-making, as understanding a patient’s history of obesity can help build a more comprehensive picture of their health, rather than BMI at the start of treatment alone.

‘Because body weight can determine chemotherapy dose, this could also lead to more personalized care.’

Experts emphasized that the increased use of weight-loss vaccines, now available at home, such as Wegovy and Mounjaro, could further change obesity patterns in cancer patients, making weight monitoring over time more important than ever.

‘One of the future challenges in understanding this complex relationship will be the increasing availability and exposure of patients to GLP-1s and other treatments being developed for use in diabetes and weight loss, and longitudinal BMI measurements are likely to become even more important,’ they said.

‘Time will tell whether expanding the use of GLP-1 reduces obesity in patients receiving systemic anticancer therapy; ‘We will understand the benefits and risks of these drugs used in conjunction with systemic therapy and determine whether GLP-1 receptor agonists have a positive effect on cancer outcomes.’

Health charities welcomed the findings, saying the research was timely in a population with little exposure to weight-loss interventions.

Dr Crocker said: ‘Our previous research has highlighted how the lack of accurate pre-diagnostic body weight measurements in studies of people living with and post-cancer presents limitations in interpreting the role of BMI on outcomes.

It’s great to see us funding research that addresses important questions for which we’ve been missing data.’

The International Agency for Research on Cancer identified 13 types of cancer linked to obesity in 2016.

These included breast, intestine, uterus, kidney, pancreas, esophagus, gallbladder, liver, upper kiss, myeloma, meningioma (a type of brain tumor), and thyroid cancer.

This does not mean that everyone who is overweight or has a history of obesity will get cancer.

In 2024, experts from Lund University in Sweden identified 19 more types of cancer that appeared to be linked to excess weight; In addition to stomach tumors, small intestine and pituitary gland cancers, ear and neck cancer, vulva and penis cancer types were also added to the list.