OBESITY, WEIGHT-GAIN, LARGE WEIGHT CHANGES, AND ADENOMATOUS POLYPS OFTHE LEFT COLON AND RECTUM

Epidemiologic studies of colorectal neoplasia have usually examined bo dy mass index as a risk factor, but not other aspects of obesity. Duri ng 1991-1993, the authors obtained weight histories and comprehensive covariate data from men and women aged 50-75 years who underwent sigmo idoscopy at a health maintenance organization in southern California. Using 483 cases with adenomas and 483 controls, measures of obesity (b ody mass index), positive energy balance (net weight gain in the past 10 years), and weight variability (large weight changes) were each ind ependently related to adenoma prevalence. Compared with subjects in th e lowest quartile of body mass index, multivariate-adjusted odds ratio s for subjects in increasingly higher quartiles were 2.1 (95% confiden ce interval (CI) 1.4-2.3), 1.8 (1.1-2.9), and 1.7 (1.0-2.8), respectiv ely, Compared with subjects who reported a net weight loss during the 10 years before sigmoidoscopy, subjects with net weight gains of 1.5-4 .5 kg or greater than or equal to 4.5 kg had adjusted odds ratios (95% CI) of 2.5 (1.2-5.6) and 1.8 (0.7-4.4), respectively. Compared with s ubjects who had no large weight changes during adulthood, subjects wit h 1-2, 3, or greater than or equal to 4 changes had adjusted odds rati os (95% CI) of 2.0 (1.0-3.9), 2.5 (1.2-5.5), and 1.5 (0.6-3.6), respec tively. Obesity, weight gain, and unstable adult weight may be indepen dently associated with colorectal carcinogenesis.