Why didn these trials show a protective effect of dietary changes or fiber supplements on colorectal polyps?
The scientists offered several possible reasons why these study designs did not show an effect of diet on polyp recurrences, including: • Development of colorectal cancer takes decades, and an intervention of three to four years may not be long enough to make a difference. Continuing follow-up of these patients may lead to further understanding of the long-term impact of dietary interventions. • Participants in these studies all had at least one polyp previously removed. Nutritional factors may influence critical molecular, cellular, or tissue-level events in colorectal cancer formation well before polyps are formed. • In these studies, the recurrent polyps the new polyps that develop after the first ones are removed tended to be small. Dietary changes might affect only the growth of small polyps into large polyps or large polyps into invasive cancer. • Why look at diet to prevent polyps? Dietary factors are believed to influence colorectal cancer risk, and polyps are considered a mid-
