Although cancer-causing substances are often thought by the general public to be synthetic, there are numerous carcinogens that occur in nature, and in food plants. (Concon,1988)
For example, tannins occur widely in plant foods and we ingest them daily in tea, coffee, and cocoa. Tannic acid has caused liver tumors in experimental animals, and may be linked to esophageal cancer in humans.
Cycad plants are important food sources in tropical regions. Cycads contain cycasin and related azoxyglycosides that were found to cause liver and kidney tumors when fed to rats.
Safrole, which is a liver carcinogen in rats, is found in sassafras tea, cinnamin, cocoa (trace), nutmeg, and other herbs and spices.
Black pepper was found to be carcinogenic to experimental mice. Pyperadine and alpha-Methylpyrroline are secondary amines in black pepper which can be nitrosated to N-nitrosopiperadine, a strong carcinogen.
Although not of plant origin, heterocyclic amines in cooked meats have been associated with stomach and other cancer formation.
Aflatoxins and Ochratoxin A are natural toxins made by fungal food contaminants that also cause cancer in animals and humans.
Some scientists maintain that research and regulatory resources have been too focussed on the problem of pesticide residues in food as potential carcinogens, while ignoring the problem of natural carcinogens. Perhaps the most well-known proponent of this opinion is Dr. Bruce Ames. Click here for a summary: POLLUTION, PESTICIDES, AND CANCER: MISCONCEPTIONS. Bruce N. Ames and Lois S. Gold.
How much do natural plant carcinogens contribute to the incidence of cancer in human populations? The answer is still unknown, but the National Research Council has reported that excess calories pose more of a cancer threat than natural or synthetic carcinogens in food.
Carcinogens and Anticarcinogens in the Human Diet - Executive Summary
Prepared Summer 1997 by Bernadene Magnuson, Ph.D.
University of Idaho, Dept. of Food Science and Toxicology - EXTOXNET FAQ Team.