June 1 (HealthDay News) -- People who are obese are less apt to have thoroughly cleansed their colon before getting a colonoscopy, hampering the effectiveness of the procedure, a new study finds.

Being obese increases the risk for several gastrointestinal issues, including colon cancer, which is most effectively diagnosed by identifying colon polyps during a colonoscopy. However, failing to properly cleanse the colon can result in the polyps not being detected during the procedure.

The study, published in Clinical Gastroenterology and Hepatology, found that more than one in four of 1,588 people who had colonoscopies had what was called an "inadequate examination." The higher a person's body-mass index (BMI), a measure of body fat based on height and weight, the greater the chance of not having adequately prepared for the procedure, the study found.

"Our results suggest that the obese patient should at least be subject to more precise instructions and possibly a more rigorous bowel preparation regimen," study author Dr. Brian Borg, of Washington University in St. Louis, said in a news release from the journal's publisher. "In addition, as the number of risk factors for an inadequate bowel preparation increase, the need for early repeat colonoscopy escalates."

SOURCE: Gastroenterological Association, news release, June 1, 2009