Diet and nutrition as risk factors for cancer.

Involvement of diet and nutrition as risk factors for human cancers has been established by two general types of evidence. Epidemiological studies in human populations have identified associations between patterns of incidence for various forms of cancer and diet composition or food consumption patterns. Such associations are particularly evident in studies on migrant populations and in patterns of geographic localization of specific forms of cancer. Reduction in gastric cancer (and increase in colon cancer) incidence has been observed in immigrants from Japan to the U.S. via Hawaii with concurrent change in dietary habits. High fat consumption has been linked to increased incidence of breast and colon cancer, and evidence is accumulating that suggests increased intake of dietary fiber (or some specific component of it) may be associated with diminished risk of colorectal cancer. Laboratory studies have demonstrated the existence of dietary constituents that might impact cancer risk in people consuming them. Substances in this class fall into two general categories: genotoxic carcinogens/mutagens; and protective factors which inhibit experimentally-induced chemical carcinogenesis in animals. Numerous naturally-occurring carcinogens/mutagens have been identified. Examples include aflatoxins, cycasin, and bracken fern carcinogen(s), among others. Genotoxic substances associated with the use of intentional food additives are the N-nitroso compounds formed as nitrosation products from nitrite. Potential carcinogenic risk from food constituents also comes from mutagens found in foods as natural components, or formed in the course of cooking.(ABSTRACT TRUNCATED AT 250 WORDS)