Risk of colorectal cancer after weight loss in the obese: a pooled cohort study

Though the link between obesity and colorectal cancer (CRC) is convincing, the impact of weight loss after obesity on CRC risk is unknown.

This pooled study from the Multiethnic Cohort, Nurses' Health Study and Health Professionals Follow-Up Study included adults aged 45-75, with 3+ available body mass index (BMI) measures. The primary analysis included persons of all weights, with exposure (BMI) subjected to group-based trajectory modeling. Time-to-incident CRC was evaluated using accelerated failure time models. A subanalysis evaluated the risk of CRC in persons with obesity who had weight loss, compared to persons with stable obesity.

A total of 193,046 persons were analyzed (median age 49 years, 66% female). Among persons with severe degrees of obesity who lost weight, there was a longer CRC-free duration in whites (acceleration factor [AF] 2.30, 95% confidence interval [CI] 1.23-4.29; P=0.01), persons of "Other" race (AF 2.54, 95%CI 2.45-2.63; P<0.001), Asian/Native Hawaiian/Other Pacific Islanders (AF 1.11, 95%CI 1.06-1.18; P<0.001), and Black/African Americans (AF 1.09, 95%CI 1.07-1.10; P<0.001). BMI was not associated with altered CRC risk in Hispanic/Latinos. Among 40,606 persons with obesity who had weight loss, higher degrees of weight loss were associated with a longer CRC-free duration. While weight loss of 5-10% had an AF of 1.14 (95%CI 1.04-1.24; P=0.01), the optimal degree of weight loss was 15-20%, AF 1.53 (95%CI 1.28-1.83; P<0.001).

Weight loss after obesity is associated with a lower CRC risk in diverse populations. In persons with obesity, 15-20% weight loss appears to be optimal.