Polyp Prevention Trial

OBJECTIVES:

The primary objective of the Polyp Prevention Trial (PPT) is to determine whether a low fat, high fiber, high vegetable and fruit eating plan will decrease the recurrence of adenomatous polyps of the large bowel. Secondary objectives of the PPT include 1) evaluating the effectiveness of the intervention program with respect to participant achievement of dietary goals; 2) examining the relation of dietary change and biochemical markers in blood; and 3) assessing the impact of the intervention on quality of life indicators.

BACKGROUND:

Nearly 60,000 men and women will die from large bowel cancer in the United States this year, making it the second leading cause of death from malignant disease in this country. The evidence that diet plays a key role in large bowel carcinogenesis is strong and growing. The PPT was undertaken because it is unlikely, with respect to diet and large bowel cancer, that any combination of further animal research, clinical investigations employing non-neoplastic endpoints, or observational epidemiologic studies would be sufficiently persuasive to influence public health policy.

A large body of ecologic, analytic epidemiologic, human metabolic, and animal experimental data suggests that three dietary factors increase the risk of large bowel cancer: high dietary fat, low dietary fiber, and low vegetable and fruit intake. Previous dietary intervention studies have generally focused on a single nutrient. The PPT is unique in that three dietary factors are being investigated simultaneously through intervention with a realistic, comprehensive dietary pattern change. NCI investigators adopted this multiple-goal dietary intervention strategy in the PPT for several reasons: people eat foods, not isolated nutrients; there may be unknown protective food constituents not encompassed in a single-nutrient intervention; and there may well be important synergistic effects of various food components best captured in a comprehensive, multifactor dietary pattern. Moreover, by embracing three promising dietary hypotheses simultaneously, the PPT intervention is intended to maximize the possibility of reducing polyp recurrence. The direct demonstration of any effect of diet on the large bowel neoplastic process would be a major advance.