Dietary risk factors and colorectal adenomatous polyps
ACP J Club. 1993 July-Aug;119:30. doi:10.7326/ACPJC-1993-119-1-030
Neugut AI, Garbowski GC, Lee WC, et al. Dietary risk factors for the incidence and recurrence of colorectal adenomatous polyps. A case-control study. Ann Intern Med. 1993 Jan 15:118:91-5.
To determine the association between dietary risk factors and the incidence and recurrence of colorectal adenomatous polyps.
2 case-control studies (1 for incidence and 1 for recurrence).
3 university-based colonoscopy practices.
Between 1986 and 1988, 2443 eligible participants, aged 35 to 84 years, with no history of colorectal cancer or inflammatory bowel disease, had colonoscopy at least to the splenic flexure. Participants in the incidence-case group (162 men and 124 women) and incidence-control group (210 men and 270 women) had no history of polyps. Participants in the recurrence-case group (130 men and 56 women) and recurrence-control group (187 men and 143 women) had a self-reported history of polyps of which a subset were confirmed pathologically as adenomatous polyps.
Assessment of risk factors
Participants were interviewed to assess food intake for 3 to 5 years before colonoscopy. Caloric intake, total fiber, saturated fat, protein and vitamin consumption, and obesity (Quetelet index) were calculated. Lowest quartiles of each were given a value of 1.0 for the odds ratio (OR) calculations, and results were reported for comparison, with the highest quartile adjusted for age and obesity.
Main outcome measures
Pathologically confirmed incident and recurrent polyps during colonoscopy.
For women, the dietary risk factors associated with incident polyps were increased saturated fat (OR 2.3, 95% CI 0.9 to 5.8), increased meat-to-fish and meat-to-chicken ratio (OR 1.9, CI 1.0 to 3.6), and decreased vitamin A (OR 0.4, CI 0.2 to 0.9). For recurrent polyps in women, the dietary risk factors were increased total fat (OR 4.4, CI 1.0 to 19.5), saturated fat (OR 3.8, CI 1.0 to 14.9), and decreased fiber (OR 0.2, CI 0.1 to 0.5). For men, no dietary factors were associated with incident or recurrent polyps except increased caloric intake (OR for both 0.5, CI for incident polyps 0.2 to 0.8, and CI for recurrent polyps 0.3 to 1.0).
For women, the association of colorectal adenomatous polyps with dietary factors varied in strength and direction. Increased saturated fat was associated with the development and recurrence of adenomatous polyps in women. In men, only increased caloric intake was associated with the risk for new or recurrent polyps.
Sources of funding: National Cancer Institute and the Aaron Diamond Foundation.
For article reprint: Dr. A.I. Neugut, Department of Medicine, Columbia Presbyterian Medical Center, 630 West 168th Street, New York, NY 10032, USA. FAX 212-305-9413.
For colorectal carcinoma, the second most common cause of cancer mortality in the United States, and for its precursor the adenomatous polyp, the evidence continues to support the hypothesis that diet is a risk factor for cancer. Macronutrients of greatest interest include saturated fats, dietary fiber, and protein. Among micronutrients, calcium, selenium, aromatic isothiocyanates, indoles, and vitamins have all been considered to be potential risk factors. Theoretical explanations for the role of each of these nutrients are intriguing, but clearly additional research is required.
The article by Neugut and colleagues is a superb addition to this body of medical research. The authors did an excellent job with many methodologic issues, including controlling for known confounders, using clear definitions of cases and controls by obtaining colonoscopy in all participants to minimize misclassification, and using a previously published and validated dietary questionnaire. The major limitation of this case-control study, not unexpectedly, is patient-recall bias. This study also did not examine meal frequency as a potential risk factor, which may be as important as what you eat (1).
Why were the findings of interest significant in women only and not in men? The answer remains unclear, but this certainly does not let men off the dietary hook. For an example, a well-designed cohort trial examining the relation between dietary factors and adenomatous polyps in professional men found an increased risk for polyps in those men who consumed a diet high in saturated fat and low in dietary fiber (2). So, keep reaching for those bran muffins, and pass the broccoli, please.
James Shaw, MD
University of North Carolina Chapel Hill, North Carolina, USA