Carcinogenicity and Anticarcinogenicity

1- Current epidemiologic evidence suggests the importance of protective factors in the diet, such as those present in fruits and vegetables.
Current evidence suggests that the contribution of excess macronutrients and excess calories to cancer causation in the United States outweighs that of individual food microchemicals, both natural and synthetic. This is not necessarily the case in other parts of the world.

2- Epidemiologic data indicate that alcoholic beverages consumed in excess are associated with increased risk for specific types of cancer.

3- Given the greater abundance of naturally occurring substances in the diet, the total exposure to naturally occurring carcinogens (in addition to excess calories and fat) exceeds the exposure to synthetic carcinogens. Regarding dietary exposure, the c ommittee reviewed data, including those generated by the Department of Agriculture and the Department of Health and Human Services through the Nationwide Food Consumption Surveys, the National Health and Nutrition Examination Surveys, and other related da ta bases. However, data are insufficient to determine whether the dietary cancer risks from naturally occurring substances exceeds that for synthetic substances (e.g., these databases do not include concentration data on many of the potential carcinogeni c constituents found in foods). Indeed, at the present, quantitative statements cannot be made about cancer risks for humans from specific dietary chemicals, either naturally occurring or synthetic.

4- Current regulatory practices have applied far greater stringency to the regulation of synthetic chemicals in the diet than to naturally occurring chemicals. The committee reviewed data and findings of IARC, the National Toxicology Program (NTP), a nd in the general literature to ascertain the status of carcinogenicity testing of naturally occurring versus synthetic chemicals. Only a very small fraction of naturally occurring chemicals has been tested for carcinogenicity. Naturally occurring dieta ry chemicals known to be potent carcinogens in rodents include agents derived through food preparation, such as certain heterocyclic amines generated during cooking, and the nitrosamines and other agents acquired during food preservation and storage, such as aflatoxins and some other fungal toxins.

5- The human diet also contains anticarcinogens that can reduce cancer risk. For example, the committee evaluated relevant literature on antioxidant micronutrients, including vitamins A, C, E, folic acid, and selenium, and their suggested contributio ns to cancer prevention. Human diets that have a high content of fruits and vegetables are associated with a reduced risk of cancer, but the specific constituents responsible for this protective effect and their mechanisms of action are not known with ce rtainty. The vitamin and mineral content of fruits and vegetables might be important factors in this relationship. In addition, fruits and vegetables are dietary sources of many non-nutritive constituents, such as isoflavonoids, isothiocyanates and othe r sulfur-containing compounds, some of which have inhibited the carcinogenic process in experimental animal studies. Foods high in fiber content are associated with a decreased risk of colon cancer in humans, but it is not yet clear that fiber per se is the component responsible for this protective effect.

6- Carcinogens and anticarcinogens present in the diet can interact in a variety of ways that are not fully understood. This makes it difficult to predict overall dietary risks based on an assessment of the risks from individual components due to unc ertainties associated with rodent-to-human extrapolation and high-dose to low-dose extrapolation. It is likely that there is also considerable interindividual variation in susceptibility to specific chemicals or mixtures due to either inherited or acquir ed factors.