Recommendation 14 Background

Phytochemicals are substances naturally found in plant foods like fruits, vegetables and grains. They are also known as phytoprotectants or bioactive compounds. Phyto is Greek for plant. Phytochemicals are not considered essential yet, in the way vitamins and minerals are.

Until the 1980's vitamins and minerals were considered important because they protected us against diseases caused by a deficiency of a given vitamin or mineral. The deficiency was clinically observable. A new concept began to emerge then: intakes above minimum recommended levels might be protective against chronic deficiencies. This was followed by the realization that substances, other than vitamins and minerals, and which are present naturally in foods may also be protective. These substances are the phytochemicals.

The exciting news about phytochemicals is their ability to inhibit carcinogenesis. Phytochemicals are capable of halting that process at one or more of the stages. They play a variety of roles such as antioxidants, suppressors of tumor growth, antimutagens, enzyme modulators, chemical inactivators, and free radical scavengers.

Most of the evidence on the beneficial effects of phytochemicals comes from laboratory studies. (Cancer was induced in animals by various chemical carcinogens and specific amounts of phytochemicals were fed to them.) This evidence suggests it may be possible that phytochemicals protect against human cancer but is not yet conclusive. In addition, under certain circumstances phytochemicals show the potential to promote cancer. More research needs to be done to confirm laboratory findings. Phytochemicals may also be significant in the prevention of other diseases such as heart disease.


In the view of the AICR/WCRF panel allium compounds possibly decrease the risk of stomach cancer; there is at present insufficient evidence that isoflavones decrease the risk of breast cancer.


Phytochemicals Food sources
Allium compounds

Dithiolthiones & isothiocyanates

Terpenoids: D-limonene, geraniol, menthol,and carvone

Phytoestrogens: lignans & isoflavones

Phenolic compounds: ellagic caffeic acids, curcumin, flavonoids (catechins) and flavonols (quercetin)


Protease inhibitors

Phytic acid (inositol hexaphosphate)

Glucosinolates: indole-3-carbinol

Plant sterols



Allium vegetables: onions, garlic, scallions, chives

Cruciferous vegetables: broccoli, cabbage, cauliflower, brussel sprouts

Oil of citrus fruit peel (used as flavoring agent in ice cream, sweets, baked goods, gelatins, puddings, chewing gum)

Cereals, legumes (lentils, beans, split peas, etc.), sorghum, millet, soybeans, wholegrain products, seeds, fruits and berries

Berries, tomatoes, potatoes, broad beans, broccoli, Italian squash, onions radishes, horseradish, kale, endive, and many other fruits and vegetables, teas walnuts, pecans

Vegetable oils, whole grains, nuts and seeds

Cereals: barley, wheat, oats and rye; legumes: soy beans, kidney beans, chickpeas, lentils and others

Cereals, nuts, seeds and legumes

Cruciferous vegetables: broccoli, cabbage, cauliflower, brussel sprouts


Soy beans

Vegetables, particularly cassava, citrus fruits and some herbs

For more information on phytochemicals visit the web site of the Center for Alternative Medicine at

For more information on carcingenesis, please see the Extoxnet TIB on Carcinogenesis.

For other details see Recommendation 14 Vitamins, Recommendation 14 Minerals. For practical advice, see Recommendation 14 How to

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Prepared 1998 by Bernadene Magnuson, Ph.D.
University of Idaho, Dept. of Food Science and Toxicology - EXTOXNET FAQ Team.