Overweight, Obesity May Be Larger Risk Factor for Colorectal Cancer Than Previously Thought


Prediagnostic weight loss could be an important marker for colorectal cancer diagnosis.

Overweight and obesity could be larger risk factors for colorectal cancer (CRC) than prior evidence indicates, according to a study published in JAMA Network Open. Studies that do not consider prediganostic (cancer-associated) weight loss may be underestimating how excess body fat factors into the risk for CRC.

Credit: Adobe Stock - Michail Petrov

Credit: Adobe Stock - Michail Petrov

“Most epidemiological studies investigating the association of excess weight with CRC risk ascertained body weight at a single point in time,” the study authors wrote. “In case-control studies, body weight is usually assessed shortly before or after cancer diagnosis, at which point the patients might have already lost considerable weight.”

In 2016, more than 2 billion adults worldwide were overweight, defined as a body mass index (BMI) between 25 and 30, or obese with a BMI of 30 or above. People with obesity have a 30% greater risk of CRC compared to people with normal weight, according to recent systematic reviews.

Most clinical studies may not account for the average 3 to 6 years of cancer-associated weight loss when they evaluate BMI and CRC risk, according to the authors of the current study. They further noted that not accounting for prediagnostic weight loss could result in underestimating the degree by which excess body fat impacts CRC risk.

The current study aims to address this selection bias. Investigators analyzed how prediagnostic weight loss could impact the relationship between excess weight and CRC risk.

From 2003 to 2021, investigators in southwest Germany conduced a large-scale population-based case-control study of 11,887 participants to evaluate the association between CRC risk and BMI. They calculated BMI at various points in time prior to CRC diagnosis, focusing on weight changes in the 12 years leading up to cancer diagnosis.

Measuring BMI 8 to 10 years prior to CRC diagnosis increased the positive association between overweight, obesity, and 5-unit BMI increase with the risk of CRC.

“High BMI as a risk factor for CRC was increased as earlier periods before diagnosis were examined, with the association being particularly pronounced using BMI at least 8 years before diagnosis,” the investigators wrote in the paper.

The findings suggest that evaluating BMI further back in time increased the BMI-CRC association for all measures of excess weight, more pronounced at a period of 8 to 12 years. When comparing people diagnosed with CRC to healthy controls, those with CRC were also more likely to have less education and a family history of CRC, currently smoke, drink more alcohol, have diabetes, and were less likely to use statins than controls.

Study limitations include that weight was self-reported and the relationship between BMI and CRC may be underestimated; contrastingly, a healthier and better-educated control group could result in overestimation. Finally, the study was only focused on overweight, obesity, and weight gain in adulthood, despite high BMI in early life being a possible risk factor.

“Our study points to involuntary prediagnostic weight loss as a potential marker for early detection of CRC,” the study authors wrote. “It appears plausible to assume that it may play a similarly important role for other cancers and noncancer diseases associated with overweight and obesity, which should be addressed in further research.”


Mandic M, Safizadeh F, Niedermaier T, et al. Association of Overweight, Obesity, and Recent Weight Loss With Colorectal Cancer Risk. JAMA Netw Open. 2023;6(4):e239556. doi:10.1001/jamanetworkopen.2023.9556

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