Carcinogens in the diet vs. overnutrition. individual dietary habits, malnutrition, and genetic susceptibility modify carcinogenic potency and cancer risk

Chemical carcinogens in the diet cannot explain the cancer incidence attributed by epidemiologists to dietary factors when the calculation is based on average exposure levels and conservative estimates of carcinogenic potencies. In a previous review, the discrepancy was explained primarily by overnutrition to which a carcinogenic potency was assigned from dietary restriction experiments and the associated reduction in spontaneous tumor incidence (W.K. Lutz and J. Schlatter, Chemical carcinogens and overnutrition in diet-related cancer, Carcinogenesis 13 [1992] 2211-2216). Here, additional aspects are introduced. They focus on using individual rather than averaged data, both for exposure and susceptibility. First, under conditions of a sublinear (convex) dose-response, the cancer incidence obtained by using an average exposure level is lower than if individual exposure levels associated with particular dietary habits are taken into account. Second, carcinogenic factors, including those unrelated to the diet (e.g., smoking), can act synergistically. Third, the potency of dietary carcinogens is increased under conditions of malnutrition in the sense of a deficiency of protective factors, such as those available with fruits, vegetables, and fibers. Quantitatively, this aspect may be particularly important because it simultaneously increases the efficacy of a multitude of carcinogens. It is concluded that chemical carcinogens could be as important as overnutrition for diet-related cancer.