MedicalResearch.com Interview with:
Dr Andrew Kunzmann & Dr Helen Coleman
Joint first authorsCentre for Public Health
Queen’s University Belfast
Medical Research: What is the background for this study?
Response: There is now a large amount of evidence to suggest that individuals who consume diets high in fiber tend to be at a lower risk of bowel (colorectal) cancer. However, it is not known whether this association begins at the early stages of bowel cancer development or at later stages, in individuals with polyps (adenomas) that can lead to bowel cancer if left untreated. The best source of dietary fiber (cereals, fruit or vegetables) for bowel adenoma and cancer prevention is also debatable.
We analysed data from individuals taking part in a large U.S trial assessing bowel screening, who completed a dietary questionnaire and received sigmoidoscopy screening at the start of the trial and received further screening 3 to 5 years later. This allowed us to investigate whether individuals with higher fiber diets had a lower risk of developing their first left-sided adenoma, but also for having adenomas recur at a later time, or indeed risk of bowel cancer, than individuals with diets low in fiber. By analysing only the screened participants, everyone had an equal opportunity to have their recurrent adenomas diagnosed – something that previous studies of dietary fiber have been unable to address.
Medical Research: What are the main findings?
Response: We found that individuals with diets high in fiber were at a lower risk of developing their first left-sided adenoma or left-sided (distal) colon cancer than individuals with diets low in fiber. These protective associations were strongest for fiber from cereals and fruit. In individuals with adenomas detected and removed at the start of the study there was no difference in risk of adenomas recurring between individuals with high fiber and low fiber diets. Therefore, the beneficial effects of fiber may begin at the early stages of bowel cancer development, before polyps have grown.
Medical Research: What should clinicians and patients take away from your report?
Response: It should be acknowledged that this study was observational and not a randomised controlled trial of diet, so the link between fiber and lower risk of polyps may not be causative. Nevertheless, the take-home message for clinicians and patients should be that current recommendations to the general public about achieving fiber-rich diets (containing at least 20 to 35 grams of fiber each day) are supported by evidence. The general public should be encouraged to eat a diet containing plenty of fiber-rich fruits and vegetables, and choose fiber-rich, wholegrain cereals or breads over lower fiber alternatives where possible. High fiber diets may be particularly important for people who regularly eat processed meats such as hot dogs or bacon, which have been linked with a higher risk of bowel cancer. Food retailers can also play a role by increasing the availability of fiber-rich foods.
Although we didn’t find an association for fiber and patients who had a recurrent adenoma, it is possible that individuals with the lowest intakes at the time of the study questionnaire later changed their diet to include more fiber, as a result of their first adenoma diagnosis. Therefore, clinicians should continue to advise patients to eat a high fiber diet, regardless of whether they have had a previous history of adenomas.
Medical Research: What recommendations do you have for future research as a result of this study?
Response: Randomised controlled trials assessing the impact of increased fiber intakes on risk of colorectal cancer amongst the general population, rather than only high-risk groups (for example those with a history of adenomas) as used previously in trials, may help confirm our findings that fiber is most protective against initial adenoma development. Additionally, research into ways of helping people to achieve and maintain adequate fiber intakes in their diet could prove valuable.
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Dr Andrew Kunzmann & Dr Helen Coleman (2015). High Fiber Diets Linked To Lower Risk of Colon Polyps and Cancer