Efficacy of a diet intervention can only be determined if people adhere to it, but adherence is often challenging. Instead, effectiveness studies focus on how well people can follow the advice in the real world. In a colonoscopy trial, only 40% complied with the recommended frequency of once every 10 years. Some studies suggest that colon cancer can develop even sooner than that. The risks of colonoscopy include bowel prep, sedation, and procedural risks like bleeding and perforation.