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Other common name(s):
antioxidants, flavonoids, flavones, isoflavones, catechins,
anthocyanidins, isothiocyanates, carotenoids, allyl sulfides,
polyphenols
Scientific/medical name(s):
various names
Description
The term "phytochemicals" refers to a wide variety of
compounds produced by plants. They are found in fruits, vegetables,
beans, grains, and other plants. Scientists have identified thousands
of phytochemicals, although only a small fraction has been studied
closely. Some of the more commonly known phytochemicals include beta
carotene, ascorbic acid (vitamin C), folic acid, and vitamin E (see
separate documents on Vitamin A
and Beta Carotene, Folic
Acid, Vitamin C,
Vitamin
E).
Overview
Some phytochemicals have either antioxidant or hormone-like actions. There is some evidence that a diet rich in fruits, vegetables, and whole grains reduces the risk of certain cancers and other diseases, and researchers are looking for specific compounds in these foods that may account for the beneficial effects in humans. Available scientific evidence does not support claims that taking phytochemical supplements is as helpful as consuming the fruits, vegetables, beans, and grains from which they are taken.
How are they promoted for use?
Phytochemicals are promoted for the prevention and treatment of many health conditions, including cancer, heart disease, diabetes, and high blood pressure. There is some evidence that certain phytochemicals may help prevent the formation of potential cancer-causing substances (carcinogens), block the action of carcinogens on their target organs or tissue, or act on cells to suppress cancer development. Many experts suggest that people can reduce their risk of cancer significantly by eating more fruits, vegetables, and other foods from plants that contain phytochemicals.
There are several major groups of phytochemicals.
The polyphenols include a large subgroup of chemicals called flavonoids. Flavonoids are plant chemicals found in a broad range of fruits, grains, and vegetables. They are being studied to find out whether they can prevent chronic diseases such as cancer and heart disease. The flavonoids found in soybeans, soy products, garbanzo beans, chickpeas, and licorice may mimic the actions of the female hormone estrogen (see Licorice and Soybean). Estrogen-like substances from these plant sources are called phytoestrogens. They may play a role in the development of some hormone-dependent cancers such as breast and prostate cancer.
Other polyphenols (including some flavonoids) act as antioxidants. These are thought to rid the body of harmful molecules known as free radicals, which can damage a cell's DNA and may trigger some forms of cancer and other diseases. These compounds are commonly found in vegetables such as broccoli, brussels sprouts, cabbage, and cauliflower
(see Broccoli)
and in teas (see Green Tea).
Grapes, eggplant, red cabbage, and radishes all contain anthocyanidins
– flavonoids that act as antioxidants and may protect against some
cancers and heart disease (see Grapes).
Quercetin, another flavonoid with antioxidant properties, is found in
apples, onions, teas, and red wine. Ellagic acid, found in raspberries,
blackberries, cranberries, strawberries, and walnuts, also is said to
have anti-cancer effects (see Ellagic
Acid).
Carotenoids, which give carrots, yams,
cantaloupe, squash, and apricots their orange color, are also promoted
as anti-cancer agents. Tomatoes, red peppers, and pink grapefruit
contain lycopene, which proponents claim is a powerful antioxidant (see
Lycopene).
The phytochemicals lutein and zeaxanthin, found in spinach, kale, and
turnip greens, may reduce the risk of some cancers.
Another group of phytochemicals, called allyl
sulfides, are found in garlic and onions (see document on Garlic).
These compounds may stimulate enzymes that help the body get rid of
harmful chemicals. They may also help strengthen the immune system.
What does it involve?
Phytochemicals are present in virtually all of the fruits,
vegetables, legumes (beans and peas), and grains we eat, so it is quite
easy for most people to include them in their diet. For instance, a
carrot contains more than 100 phytochemicals. There are literally
thousands of known phytochemicals, but only a few have been
studied in detail.
Many of the better-known phytochemicals are now available as
dietary supplements. However, no one knows if single supplements are as helpful
as the foods from which they are derived. In the United
States, dietary supplements are regulated differently than drugs. The
makers of dietary supplements can sell them without having to prove
they are effective, or even safe, as long as they don’t claim they can
prevent, treat, or cure a specific disease.
What is the history behind it?
Only a few years ago, the term "phytochemical" was barely
known. But doctors, nutritionists, and other health care practitioners
have long advocated a low-fat diet that includes a variety of fruits,
vegetables, legumes, and whole grains. Historically, cultures that
consume such a diet have lower rates of certain cancers and heart
disease.
Since the passage of the Dietary Supplement Health and
Education Act (DSHEA) in the United States in 1994, a large number of
phytochemicals are being sold as as dietary supplements.
What is the evidence?
It has become a widely accepted notion that a diet rich in
fruits, vegetables, legumes, and grains reduces the risk of cancer,
heart disease, and other illnesses. But only recently have researchers
begun to try to learn the effects of specific phytochemicals
contained in those foods.
Much of the evidence so far has come from observations of
cultures whose diets consist mainly of plant sources, and which seem to
have lower rates of certain types of cancer and heart disease. For
instance, the relatively low rates of breast and endometrial cancers in
some Asian cultures are credited at least in part to dietary habits.
These cancers are much more common in the United States, possibly
because the typical American diet is higher in fat and lower in fruits,
vegetables, legumes, and grains.
Because of the number of phytochemicals and the complexity of
the chemical processes they are involved in, researchers face a
challenging task in trying to determine which phytochemicals in foods
may fight cancer and other diseases, which may have no effect, and
which may even be harmful.
Many studies have looked at the relationship between cancer
risk and eating fruits and vegetables, legumes, and whole grains. Most
of the evidence indicates that eating large proportions of these foods
seems to lower the risk of some cancers and other illnesses.
Some of the links between individual phytochemicals and
cancer risk found in studies in the lab are very compelling and make a
very strong case for the need for further research. So far, however,
none of the findings is conclusive. It is still uncertain which of the many
phytochemicals in fruits and vegetables actively helps the body fight
disease.
Researchers have also shown much interest in phytochemical
supplements. Some lab studies in cell cultures and animals have shown
that certain phytochemicals have some activity against cancer cells or
tumors. But at this time there have been no strong studies in humans
showing that any phytochemical supplement can prevent or treat cancer.
Until conclusive research findings emerge, health care
professionals advise a balanced diet with an emphasis on fruits,
vegetables, legumes, and whole grains. The interaction between certain
phytochemicals and the other compounds in foods is not well understood,
but it is unlikely that any single compound offers the best protection
against cancer. A balanced diet that includes 5 or more servings a day
of fruits and vegetables along with foods from a variety of other plant
sources such as nuts, seeds, whole grain cereals, and beans is likely
to be more effective in reducing cancer risk than eating one particular
phytochemical in large amounts.
Are there any possible problems
or complications?
These products are sold as a dietary supplement in the United States. Unlike drugs (which must be tested before being allowed to be sold), the companies that make supplements are not required to prove to the Food and Drug Administration that their supplements are safe or effective, as long as they don't claim the supplements can prevent, treat, or cure any specific disease.
Some such products may not contain the amount of the herb or substance that is written on the label, and some may include other substances (contaminants). Actual amounts per dose may vary between brands or even between different batches of the same brand.
Most such supplements have not been tested to find out if they interact with medicines, foods, or other herbs and supplements. Even though some reports of interactions and harmful effects may be published, full studies of interactions and effects are not often available. Because of these limitations, any information on ill effects and interactions below should be considered incomplete.
Phytochemicals in the amounts consumed in a healthy diet are likely to be helpful and are unlikely to cause any major problems. Some people assume that because phytochemical supplements come from "natural" sources, they must be safe and free from side effects, but this is not always true. It is important to note that, especially when taken in large amounts, many of them have side effects and possible interactions with some drugs. Some of these interactions may be dangerous. Before taking a phytochemical in supplement form, consider talking to your doctor and pharmacist to be sure it won’t interact harmfully with other medicines or herbs you may be taking.
Relying on the use of phytochemicals alone, and avoiding or delaying conventional medical care, may have serious health consequences.
Additional Resources
More Information From Your
American Cancer Society
The following information on complementary and alternative
therapies may also be helpful to you. These materials may be ordered
from our toll-free number (1-800-ACS-2345).
References
Craig WJ. Health-promoting properties of common herbs. Am J Clin Nutr. 1999;70:491S-499S.
Gruenwald J, Brendler T, Jaenicke C, eds. PDR for Herbal Medicines, Third Edition. Thomson PDR, Montvale NJ, 2004.
Kushi, L.H., Byers, T., Doyle, C., Bandera, E.V., McCullough, M., Gansler, T., et al. American Cancer Society guidelines on nutrition and physical activity for cancer prevention: Reducing the risk of cancer with healthy food choices and physical activity. CA: A Cancer Journal for Clinicians 2006; 56, 254–281.
Setchell KDR, Cassidy A. Dietary isoflavones: biological effects and relevance to human health. J Nutr. 1999;129:758S-767S.
Wang YH, Chao PD, Hsiu SL, et al. Lethal quercetin-digoxin interaction in pigs. Life Sci. 2004 Jan 23;74(10):1191-7.
Note: This information may not
cover all possible claims, uses, actions, precautions, side effects or
interactions. It is not intended as medical advice, and should not be
relied upon as a substitute for consultation with your doctor, who is
familiar with your medical situation.
Revised: 06/19/2007
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