Phytochemicals – Plant Food Chemicals That Prevent Cancer
By Donald R. Davis, Ph.D.
For over 100 years, “phytochemical” was an obscure, scientific word meaning “plant chemical,” derived from the Greek word for plant. Last year, the word appeared on the cover of Newsweek and in many other magazine and newspaper
Cancer-preventing phytochemicals occur in all plant foods …
articles. Behind this transformation lies a major advance in our understanding of foods and health. This newly popular word has a much narrowed meaning. Phytochemicals are plant chemicals, in foods, that improve health and prevent disease. Usually the narrow term excludes vitamins, other essential nutrients, and substances our bodies make.
Until recently we didn’t know such phytochemicals existed. Now we know of hundreds, and expect to find thousands. Most help prevent cancer in animals, or even regress cancer, and the National Cancer Institute launched a phytochemicals project in 1989. Some scientists view phytochemicals as the “second golden age of nutrition,” the first being the discovery of vitamins and other nutrients. Some phytochemicals help prevent heart disease, hypertension, infection, and other illnesses, but here I will highlight phytochemicals that prevent cancer. Although there is still no proof of cancer prevention in humans, the proof in animals is broad, and the human evidence is highly suggestive.
Cancer-preventing phytochemicals occur in all plant foods-vegetables, fruits, whole grains, beans, nuts, seeds, garlic, spices, herbs, tea, and even wine. Few are harmed by cooking or canning. But few, if any, remain in non-whole foods-purified sugars, added fats, white flour and rice, and distilled alcohol. Unfortunately, these non-whole foods are, by far, the major plant-derived foods eaten by most Westerners.
Cruciferous vegetables include cabbage, broccoli, cauliflower, radish, and others. (The name comes from their flowers, which have only four petals, shaped like a cross.) They have perhaps the best evidence for preventing human cancer. Persons with low intakes have elevated risk for bowel cancer. In animals these vegetables and some of their components also decrease the risk of breast cancer. Cruciferous vegetables are rich in phytochemicals called isothiocyanates and indoles.
Vegetables and fruits also contain myriad other phytochemicals, including (bio )flavonoids, carotenes, chlorophylls, monoterpenes and cinnamic acids. (The last are also in cinnamon.) Over 200 human studies have found reduced risk of cancer (and other diseases) with high intakes of vegetables and fruits. These benefits often are attributed to vitamins C, E, and B-carotene, but phytochemicals may contribute importantly, too, including hundreds of carotenes other than B-carotene. Red wine retains quercetin and other flavonoids found in grape skins. These phytochemicals are known best for preventing heart disease, but they also prevent cancer in animals. Purple grape juice is a lesser source.
Citrus fruits and some seeds such as caraway contain phytochemical oils called monoterpenes. These induce liver enzymes that detoxify carcinogens. Remarkably, they also regress some established tumors in animals. Garlic and onions contain diverse sulfur- and selenium-containing phytochemicals. They detoxify or block carcinogens, damage tumor cells, and inhibit tumor growth in animals. They stimulate the immune system, including that of AIDS patients. Some claim one can’t get much benefit without “garlic breath,” but most positive studies used cooked garlic, pickled garlic, aged garlic, and garlic extracts that have little odor.
Phytochemicals in teas, spices, and herbs are the subject of an entire scientific book (1994). Ten chapters deal with tea, especially green tea, the Chinese favorite. American tea is black tea. Both come from cut leaves of the same plant, but green tea is quickly heat treated, whereas black tea is allowed first to oxidize in air for several hours. This oxidation destroys some beneficial flavonoid polyphenols in tea. Oolong tea is between green and black tea. Herb teas presumably contain their own phytochemicals, but these have received little notice so far.
Consumption of whole grains, beans, nuts, and seeds favors low rates of bowel cancer and other cancers, often attributed to the fiber in these foods. Now we must wonder if phytates, flavonoids, or other phytochemicals are partly or mostly responsible. Phytates once were considered undesirable because they bind zinc, iron, and other minerals.
If fruits and vegetables help prevent strokes, what is the mechanism that makes it possible? The researchers explored many possibilities.
First, they examined the effect of fruits and vegetables on blood pressure, a major determinant in strokes. Rouse and associates, back in 1983, showed that vegetarian diets lowered blood pressure.
Next, the researchers looked at cholesterol. Since dietary soluble fiber in fruits and vegetables tends to lower cholesterol, this could be the mechanism. Only 10% of strokes are caused by plugged arteries.
Then, they looked at folate and potassium. Several recent studies have shown folate to have a lowering effect of homocysteine in the plasma. Elevated levels of homocystein are a contributor to strokes. Potassium may lower blood pressure. It is found in fruits and vegetables.
Antioxidants were also considered, but these micronutrients were missing from the data set in the 1960’s. The current data set didn’t separate the vegetables into subgroups such as citrus fruit or cruciform vegetables, such as broccoli, which research has shown valuable.
This left the researchers to conclude, without finding the mechanism, that “intake of fruits and vegetables appears to protect against the risk of stroke in men…both ischemic and hemorrhagic strokes.”
They closed with, “These results provide support to programs aimed at widespread increases in the consumption of fruits and vegetables. If successful, such programs may have beneficial effects on the incidence of stroke as well as other chronic diseases that constitute the leading causes of [sickness and death] in Western societies.”