Weight Cycling and Cancer Risk in the Sister Study.

Weight cycling, when weight is repeatedly lost intentionally and then regained, may perturb biological processes that could influence cancer development. However, results from epidemiologic studies of weight cycling are mixed and provide no clear answer as to whether this behavior alters cancer risk. We examined the association of weight cycling and cancer incidence among 45,004 women enrolled in the Sister Study (2003-2009) and followed through October 12, 2020. Weight cycling was defined using baseline responses about the number of times ≥20 pounds (9 kilograms) was lost and then regained. Multivariable-adjusted hazards ratios and 95% confidence intervals for all cancers and five individual cancers (breast, endometrial, ovarian, colorectal, and kidney) were estimated using Cox proportional hazards regression modeling. Weight cycling was not associated with an increased risk of any cancer after bodyweight was adjusted for and was inversely associated with risk of all cancers (HR 6+ episodes 0.89, 95% CI 0.80-0.97; P-trend <0.01) and breast cancer (HR 6 + episodes 0.82, 95% CI 0.69-0.97; P-trend <0.01). The inverse trend for breast cancer was only seen in obese and in postmenopausal women. These findings suggest that weight cycling, independent of bodyweight, does not increase cancer risk and, for breast cancer, is associated with decreased risk.