Researchers associated with the U.S. Polyp Prevention Trial have reported that high compliance with a low-fat, high-fiber diet is associated with a reduced risk of adenoma recurrence. The details of this study appeared in the September 1, 2009 issue of the American Journal of Epidemiology.[1]

Most researchers agree that there are good theoretical grounds to suspect that a high-fiber diet can prevent colon cancer by diluting and adsorbing out compounds in the gastrointestinal tract that cause cancer. More than 30 years ago, Burkett observed a low incidence of colon cancer in Africans eating a largely vegetable diet with over 50 grams per day of fiber. Since this observation there have been numerous studies performed to determine if patients eating a high-fiber diet have less adenomas and colon cancer. Observational studies have suggested that individuals who eat a high-fiber died have a lower risk of colon cancer when compared with individuals who eat a low-fiber diet. However, no effect on recurrent polyps was observed in prospective intervention trials, where patients with adenomas were randomly allocated to high-fiber or normal fiber diets. Thus, the role of fiber in preventing colon cancer is not certain. Nonetheless, high-fiber diets continue to be advised for the prevention of heart disease and as part of an overall healthy diet.

In addition to findings on fiber, most studies have shown that increased intake of red and processed meat is associated with an increased incidence of colorectal cancer. The effect of fats on adenomas and colorectal cancer is controversial. Studies of cancer rates across countries have suggested that a low-fat diet may be linked with a lower risk of colorectal cancer. Countries with lower average fat intake than the United States tend to have lower rates of colorectal cancer. Furthermore, individuals who move from a country with low fat intake to a country with higher fat intake tend to experience the higher colorectal cancer rates of their new country. However, according to the results of the Women’s Health Initiative Dietary Modification Trial, risk of colorectal cancer was not significantly reduced among postmenopausal women assigned to a diet low in fat and high in fruits, vegetables, and grains.

Thus, the role of fiber, fruits, vegetables, and fat in the etiology of colorectal cancer is still unclear. Researchers from the Division of Cancer Control and Population Sciences examined the effect of dietary adherence on the outcomes of the U.S. Polyp Prevention Trial conducted between 1991 and 1998. They observed a wide range of compliance among participants of this study. However, one group of 210 participants was “super compliers” and met or exceeded the dietary goals for fiber, fruits, and vegetables and fat. These “super compliers” had a 35% reduced risk of developing recurrent adenomas compared with controls. These authors concluded that “high compliance with a low-fat, high-fiber diet is associated with a reduced risk of adenoma recurrence.”

Comments: These data suggest that many of the randomized dietary trials designed to prevent recurrence of colorectal adenomas are complicated by compliance issues, which may explain why some randomized trials have failed to find an effect of diet on adenoma prevention.

Reference: