Inhibition of carcinogenesis by minor dietary constituents.

A major foundation of the field of cancer chemoprevention has resided in an impressive number of animal studies showing that cancer can be prevented by a variety of chemical compounds. In the search for increasingly effective inhibitors, both synthetic and naturally occurring compounds are being investigated. One group of naturally occurring compounds of particular interest consists of minor dietary nonnutrients. Foods of plant origin frequently contain as much as several per cent of these compounds. In recent years there has been a growing awareness that they may have important effects on the consequences of exposure to carcinogenic agents. This information comes from studies of whole diets; individual dietary constituents, particularly those from plants; and finally from investigations of pure compounds. The nonnutrient inhibitors of carcinogenesis have several different mechanisms of action. Some are blocking agents; i.e., they prevent carcinogens from reaching or reacting with critical target sites. Others are suppressing agents; i.e., they prevent evolution of the neoplastic process in cells that otherwise would become malignant. Occasionally, one compound will show both mechanisms. The nonnutrient compounds have the important attribute of there being data on their consumption by humans. Thus, it may be possible to evaluate their impact on cancer risk. Ultimately, information pertaining to these compounds may be useful in terms of diet selection or their use as dietary supplements.