Background: Obesity and adult weigh gain are established risk factors for colorectal cancer (CRC). Few studies have investigated the association between adult body weight change over time and risk of colorectal adenoma. We hypothesize adult BMI change over time is associated with risk in the development of colorectal adenomas. Methods: We tested this hypothesis in 2,993 patients undergoing screening colonoscopy from 2007–2017. Weight at age 20, 30, 40, and 50 were self-reported via computer assisted personal interviews. Height and weight at recruitment were measured at the time of colonoscopy exam. BMI (kg/m²) change was calculated as the difference of BMI at recruitment from the BMI estimate for each of the age periods. Results: Of the 2,993 patients, 984 had pathologically confirmed diagnosis of colon adenoma. Multivariate logistic regression adjusted for potential confounders and BMI at recruitment showed statistically significant increase of risk of adenoma with increase of BMI since age 30, age 40, and age 50. Compared to those with BMI change of less than 5, the ORs for those with BMI gain of 5-10 and ≥10 were: 1) 1.16 (0.92-1.46) and 1.48 (1.08-2.03) respectively for change from age 30 (p_trend = 0.05); 2) 1.11 (0.87-1.43) and 1.60 (1.09-2.35) respectively for change from age 40 (p_trend = 0.05); and 3) 1.36 (0.95-1.94) and 2.95 (1.33-6.90) respectively for change from age 50 (p_trend = 0.01). Stratified analysis did not reveal noticeable gender differences. Conclusions: Large adult weight gain over time is an independent risk factor for colorectal adenoma. Our results suggest maintaining healthy body weight throughout adulthood is an important preventive measure against the development of early colorectal neoplasia.

^a P value for linear trend.