The Obesity Paradox and Mortality After Colorectal Cancer: A Causal Conundrum

Excess body adiposity, commonly approximated as elevated body mass index (BMI; calculated as weight in kilograms divided by height in meters squared), is an established risk factor for increased incidence of several adult cancer types.¹ Worldwide, each year, almost a half-million new cancers are attributed to elevated BMI, of which breast, colorectal, and endometrial cancers account for two-thirds.² By extension, elevated BMI at or after cancer diagnosis might be associated with a poor prognosis in obesity-related cancers, and indeed, a meta-analysis³ of 82 studies have found such associations for breast cancer. This is a key rationale for weight management strategies in cancer survivorship programs and endorsed by clinical guidelines, for example, those from the American Society for Clinical Oncology.⁴