Download Dietary Natural Chemicals: Misunderstanding about Pesticide

Foods Food Ingredients J. Jpn., Vol. 214, No.3, 2009
Dietary Natural Chemicals: Misunderstanding about Pesticide Residues
Hideaki Karaki
Professor Emeritus of the University of Tokyo
Vice President of the Science Council of Japan
3-5-6-301 Honkomagome, Bunkyo-ku, Tokyo 113-0021, Japan
Summary
In 1977, Dr. Bruce N. Ames and his colleagues published an important paper entitled "Dietary
pesticides (99.99 % all natural)", in which they examined the toxicological significance of exposure
to synthetic compounds in the context of intake of naturally occurring chemicals in vegetables and
fruits.
They calculated that 99.99 % (by weight) of the pesticides in the American diet are chemicals that
plants produce to defend themselves. Only 52 natural pesticides have been tested in high-dose
animal cancer tests, and about half (27) were found to be rodent carcinogens; these 27 are in fact
present in many common foods. From these results, they concluded that natural and synthetic
chemicals are equally likely to be positive in animal cancer tests and that at the low doses of most
human exposures the comparative hazards of synthetic pesticide residues are insignificant. Their
report also suggested the possibility that consumption of vegetables and fruits could increase the
risk of cancer. Recently, the Japan Public Health Center-based Prospective Study Group (JPHC)
conducted several studies to determine the effects of fruit and vegetable intake on risk of cancer.
They found that, in the Japanese population, consumption of fruits and vegetables does not change
the risk of total cancer, lung cancer, and colorectal cancer, although vegetables and fruits
decreased the risk of gastric cancer and esophageal squamous cell carcinoma. Furthermore,
vegetables decreased the risk of hepatocellular carcinoma although fruits increased the risk. These
results are in line with vegetables and fruits containing various types of endogenous chemical
substances, some of which are carcinogenic. Given the fact that the amounts of these chemicals are
10,000 times larger than those of pesticide residues or food additives, a new perspective is needed.
Vegetables and fruits also have compounds with antioxidant activities, vitamins and minerals and,
therefore, consumption may change the risk of cancer depending on their actions in particular
tissues under particular biological conditions.