Unexplained significant weight loss, defined as losing more than 10% of body weight, may be a crucial early warning sign of bowel cancer, according to a German study. The research, published in JAMA Network Open, suggests that this weight loss is linked to a higher risk of death and cancer recurrence, potentially re-framing the long-observed "obesity paradox."
Bowel cancer is the third most common cancer globally, with an estimated 3.2 million new diagnoses expected by 2040. In the UK alone, it causes approximately 17,700 deaths annually. While obesity is a known risk factor for several cancers, including bowel cancer, previous studies have suggested that overweight or obese patients might have better survival rates than those of a healthy weight. This phenomenon, dubbed the "obesity paradox," was thought to be due to better tolerance of cancer and its treatments, or more frequent doctor visits for related health issues leading to earlier diagnosis.
However, the new study analyzed data from over 5,500 bowel cancer patients over five years. Researchers found that patients who lost more than 10% of their body weight in the five to 14 years prior to diagnosis had a 55% higher risk of death from any cause compared to those whose weight remained stable. They were also 51% more likely to die from the disease and had a 33% greater chance of their cancer returning.
When researchers accounted for this pre-diagnosis weight loss, the perceived survival advantage for overweight patients disappeared. The study concludes that the "obesity paradox" might be an artifact of this unintentional weight loss caused by hidden cancer, rather than obesity itself conferring a survival benefit. The findings emphasize that significant, unintentional weight loss should not be disregarded and warrants medical attention.
Bowel cancer is rising sharply in younger populations for reasons that are not yet fully understood. While lifestyle factors like obesity, lack of exercise, and excessive alcohol consumption contribute to the disease, obesity is the only behavioral risk factor that has increased among younger adults in recent decades. Maintaining a healthy weight is estimated to prevent about 20% of bowel cancers, but experts suggest other unknown factors, potentially including early life exposures, may also play a role in the overall increase.