After eight years of follow-up the Polyp Prevention Trial continues to show that a low-fat, high-fiber, high fruit and vegetable diet does not protect against the development of pre-cancerous colon polyps (adenomas).
The original Polyp Prevention Trial randomized men and women who had at least one adenomatous colon polyp removed during colonoscopy into intervention and control groups. At the beginning of the trial, there was little difference in diet between the two. The intervention group reduced their fat intake and increased fiber, fruits, and vegetables. The control group continued eating as usual.
Participants in the intervention group received extensive counseling and support to maintain a daily diet that included:
- no more than 20 percent of calories from fat
- 18 grams or more of dietary fiber
- 5 to 8 servings of fruits and vegetables
After four years, there was no difference in new adenomas between the two groups. Forty-percent of each group had at least one new polyp. Neither was there any difference in large adenomas or adenomas with high-risk features.
At that time in 2000, the research team concluded that
Adopting a diet that is low in fat and high in fiber, fruits, and vegetables does not influence the risk of recurrence of colorectal adenomas.
However, the researchers were concerned that four years was not sufficient time to see an impact from dietary changes, so they persuaded 1,300 of the original group to continue follow-up for an additional four years.
While the intervention group did not maintain as low a percentage of fat and decreased fruits and vegetables somewhat, they did not return to their original way of eating/ There was still a significant difference in diet between the two groups.
After an average of almost four more years, participants had another colonoscopy to evaluate pre-cancerous polyps. Again, there was no difference between risk of polyps, multiple polyps or advanced polyps between those on the special diet and those who ate as they had from the beginning of the trial.
After eight years of following the two groups, Elaine Lanza and her team at the National Cancer Institute’s Laboratory for Cancer Prevention wrote,
This study failed to show any effect of a low-fat, high-fiber, high-fruit and -vegetable eating pattern on adenoma recurrence even with 8 years of follow-up.
SOURCE: Lanza et al, Cancer Epidemiology, Biomarkers, and Prevention, Volume 16, Number 9, pages 1745-1752, September 1, 2007/


