Obesity is associated with an increased risk of colorectal adenomas - growths or polyps that can become cancerous - but weight loss might reduce the risk, a study hints.

“Colorectal cancer is known to be associated with obesity,” Dr. Yutaka Yamaji from University of Tokyo, Japan told Reuters Health. “Our data, together with previous reports, shows pre-cancerous lesions are also associated with obesity.”

Yamaji and colleagues investigated the relationship between obesity and the prevalence of colorectal polyps and studied the effect of weight loss on the development of these abnormal growths after 1 year. Almost 8000 “average-risk” subjects had an initial colonoscopy, and about 2500 of them had a second examination a year later.

The prevalence of colorectal polyps at the initial colonoscopy increased proportionally with increasing body weight, the team found. Increasing body mass index, or BMI, was also associated with increasing numbers of colorectal polyps, but not with size or stage of the polyps.

Losing weight appeared to have a beneficial impact on colorectal growths. While the incidence of polyps 1 year after the initial exam increased proportionally with increasing BMI, the researchers found that the incidence was lower in people who lost weight (9.3 percent) than in those that gained weight (16.2 percent) or maintained their weight (17.1 percent).

SOURCE: American Journal of Gastroenterology, August 2008.