Obesity directly causes changes in the gut that can lead to colorectal cancer.
This National Institutes of Health study found that “the additional weight seemed to activate more genes that are associated with colorectal cancer progression… Any preexisting colon lesions in these animals are more likely to evolve rapidly into malignant tumors. The same thing may happen in humans”.
Paul Wade, Ph.D., and Thomas Eling, Ph.D.,
Study by Li R, Grimm SA, Chrysovergis K, Kosak J, Wang X, Du Y, Burkholder A, Janardhan K, Mav D, Shah R, Eling TE, Wade, PA. 2014, scientists at the National Institute of Environmental Health Sciences (NIEHS), National Institute of Health. “Obesity, rather than diet, drives epigenomic alterations in colonic epithelium resembling cancer progression”. As published in the journal Cell Metabolism on April 1, 2014; doi:10.1016/j.cmet.2014.03.012. http://www.nih.gov/news/health/apr2014/niehs-01.htm