Dietary Fiber, Vegetables, and Colon Cancer: Critical Review and Meta-Analyses of the Epidemiologic Evidence

Author(s): Lanza, E., Greenwald, P.

Journal/Book: Journal of the National Cancer Institute. 1990; 82: 650-661.

Abstract: Whether colon cancer risk can be modified by a diet rich in vegetables, grains, and fruit, and, if so, whether the protec-tive factor is dietary fiber or other biologically active compo-nents correlated with a high-fiber diet are questions of active research interest. Because studies an diet are susceptible to bias from a number of sources, in this review we evaluated the adequacy of study methodology as well as study results to clarify how much protection, if any, is conferred by a high-fiber diet. The review consisted of an aggregate assessment of the strength of evidence from 37 observational epidemiologic studies as well as meta-analyses of data from 16 of the 23 case-control studies. Both types of analyses revealed that the majority of studies gave support for a protective effect associated with fiber-rich diets; an estimated combined odds ratio (OR) of 0.57 (95 % confidence interval = 0.50, 0.64) was obtained when the highest and lowest quantiles of intake were compared. Risk estimates based an vegetable consumption (OR = 0.48) were only slightly more convincing than those based an an estimate of fiber intake (OR = 0.58), but the data do not permit discrimination between effects due to fiber and nonfiber effects due to vegetables.

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