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Other common
name(s): soy, soya, soy protein, soy powder, glycine soja
Scientific/medical
name(s): Glycine
max
Description
The soybean plant is an annual plant native to southeast Asia.
It has oblong pods that contain 2 to 4 seeds or beans. Soybeans are
legumes, a member of the pea family and are a source of high-quality
protein. They are processed to make various foods and food additives.
Overview
In laboratory studies, animal studies, and research looking at
groups of people and their dietary habits, certain chemical components
of soy have appeared to show protective effects against breast and
prostate cancer. Randomized clinical trials are needed to understand
how these findings apply to cancer prevention in humans.
Results of research on the effects of consuming isoflavones (a
soy component) on colon cancer risk have been mixed. Some human studies
on individual soy components have been conducted and others are still
underway. Most studies that have shown benefit have used whole soy
protein rather than soy components and extracts.
How is it promoted for use?
Soybean products are promoted for their protective properties
against breast, prostate, colon, and lung cancer. The effects of soy
are thought to be due to substances called isoflavones, although other
substances may also contribute. Isoflavones are sometimes called plant
estrogens or phytoestrogens because they mimic (although weakly)
estrogen that is produced in humans and animals. Genistein, daidzein,
and glycitein are isoflavones that are present in small amounts in
other foods but are most abundant in soy.
As a protein source, soybean products are promoted as a
healthier alternative to meat and as an aid to weight loss. Soy
products are also used to lower cholesterol and blood pressure, and to
relieve symptoms of menopause and osteoporosis. Proponents also suggest
that including soy protein in a diet low in saturated fat and
cholesterol may help reduce the risk of heart disease.
What does it involve?
Soy can be consumed in many forms with tofu, soy milk, soy
powder, and textured vegetable protein being some of the more popular.
The amount of isoflavone varies by type of soy products. Soy is also
available as a dietary supplements or pill. Soy protein powders and
bars are available in nutrition stores and health food markets. The
powders can be added to drinks or used in cooking. Isoflavone
supplements are also available, although most tests that show benefit
have used whole soy protein.
What is the history behind it?
The soybean has been used as a food source for more than 5,000
years. Today, there are more than 2,500 varieties of soybeans that are
grown throughout the world. It was not until relatively recently that
studies began on the potential health promoting properties of the
soybean.
Plant estrogens were first identified in the early 1930s, when
it was discovered that soybeans, willows, dates, and pomegranates
contained compounds similar in structure to estrogens. Scientists began
studying the role isoflavones play in reducing breast cancer risk in
the 1960s. In a 1981 prospective study in Japan, researchers found that
daily intake of miso, a soybean paste, was linked to lower death rates
from stomach cancer in more than 260,000 men and women. Around that
time, other studies on soy began to be published in the United States.
In October 1999, the U.S. Food and Drug Administration (FDA) agreed to
allow health claims about soy's role in reducing heart disease on food
products containing soy protein.
What is the evidence?
Researchers believe that the isoflavones in soy, such as
genistein, daidzein, and glycitein, may play a role in reducing cancer
risk. A number of laboratory and animal experiments and human
observational studies have found that soy isoflavones may reduce the
risk of several types of cancer, including breast, prostate, and colon
cancer. However, these results have not yet been reflected in human
clinical trials, so no definite conclusions can be made.
There is enough evidence, scientists believe, for
phytoestrogens to be studied in clinical trials as an addition to
conventional breast or prostate cancer treatment. Human studies
sponsored by the National Cancer Institute are under way. Large studies
that looked at groups of women with a high soy intake showed a lower
risk of breast cancer and endometrial cancer, but there are many
possible explanations other than the soy. Further studies that control
for these factors are needed. It is also possible that the weak
estrogen-like effect of soy might be helpful in prostate cancer
prevention, but large human studies are needed.
Some studies have suggested that the effect of soy foods on
breast cancer risk depends on the age when they are consumed. It is
thought that high soy intake by young women at a time when breast
tissue is developing and estrogen levels are relatively high may offer
some protection. However, it is unclear whether soy intake after
menopause, when estrogen levels are naturally low, is of any benefit or
could even be harmful.
Several clinical studies of women with breast cancer have been
done to determine whether soy capsules help with symptoms of menopause.
The results have not shown any consistent improvement of symptoms such
as hot flashes.
Several studies of men with prostate cancer have suggested
that soy foods and/or supplements may reduce levels of
prostate-specific antigen (PSA), a substance that typically increases
as prostate cancer grows. In another study, while PSA levels did not
decrease during soy treatment, they increased less rapidly than they
had before the study began. Although these results are encouraging,
further research is needed to learn whether soy products help men with
prostate cancer to live longer.
Soybeans and soy foods have been shown in clinical trials to
lower cholesterol and reduce blood pressure.
The American Cancer Society's nutrition guidelines recommend
eating a balanced diet that includes five or more servings a day of
vegetables and fruit, choosing whole grains over processed and refined
foods, and limiting red meats and animal fats in order to help reduce
cancer risk. Using soy foods as a substitute for some servings of
animal protein is one way to reduce red meat and animal fat intake (see
Vegetarianism).
It is best to choose foods from a variety of fruits, vegetables and
other plant sources such as nuts, seeds, whole grain cereals, and
beans. (For more information, see American Cancer Society
Guidelines on Nutrition and Physical Activity for Cancer Prevention.)
Are there any possible problems or
complications?
This product is 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.
Eating soybeans is generally considered safe for those who are
not allergic to them. Side effects are rare, but may include occasional
intestinal problems such as stomach pain, loose stools, and diarrhea.
The isoflavones in soy have weak estrogen-like activity, and
it remains uncertain how they could affect the growth of estrogen
receptor-positive breast cancers. Some researchers suggest they may act
as anti-estrogens and reduce cancer growth, while others suggest their
estrogen-like activity could cause cancer to grow faster. Until this
issue is resolved, many oncologists recommend that people taking
tamoxifen or aromatase inhibitors and people with estrogen-sensitive
breast tumors should avoid adding large amounts of soy, including soy
supplements or isoflavones, to their diets.
Soy isoflavone supplements appear to be safe for most people,
although it is possible that there may be risks not yet identified.
Isoflavone supplements have not been studied in pregnant women, and
these concentrated sources may not be healthy for the fetus. Soy
products are considered safe in pregnancy.
A few people are allergic to soy proteins and may have serious
or life-threatening reactions to soy-containing foods. These people
should avoid all forms of soy and supplements made from it. Soy
ingredients may also be listed as soya.
Relying on this type of treatment alone and avoiding or
delaying conventional medical care for cancer 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 found on
our Web site (www.cancer.org)
or ordered from our toll-free number (1-800-ACS-2345).
References
Dalais FS, Meliala A, Wattanapenpaiboon N, et al. Effects of a
diet rich in phytoestrogens on prostate-specific antigen and sex
hormones in men diagnosed with prostate cancer. Urology.
2004;64:510-515.
Fournier DB, Erdman JW Jr, Gordon GB. Soy, its components, and
cancer prevention: a review of the in vitro, animal, and human data. Cancer Epidemiol Biomarkers Prev.
1998;7:1055-1065.
Gruenwald J, Brendler T, Jaenicke C, eds. PDR for Herbal Medicines,
Third Edition. Thomson PDR, Montvale NJ, 2004.
Henkel J. Soy: Health claims for soy protein, questions about
other components. US Food and Drug Administration. Accessed at:
http://www.fda.gov/fdac/features/2000/300_soy.html on June 10, 2008.
Jacobsen BK, Knutsen SF, Fraser GE. Does high soy milk intake
reduce prostate cancer incidence? The Adventist Health Study. Cancer Causes Control.
1998;9:553-557.
MacGregor CA, Canney PA, Patterson G, McDonald R, Paul J. A
randomised double-blind controlled trial of oral soy supplements versus
placebo for treatment of menopausal symptoms in patients with early
breast cancer. Eur J
Cancer. 2005;41:708-14.
MD Anderson Cancer Center. Herbal/Plant Therapies: Soy
(Glycine max[L.] Merr.) Accessed at:
www.mdanderson.org/departments/cimer/display.cfm?id=4B0FB06E-7655-4487-9146CCE58AA7D403&method=displayFull&pn=6EB86A59-EBD9-11D4-810100508B603A14
on June 10, 2008.
Messina M. Soy, soy phytoestrogens (isoflavones), and breast
cancer. Am J Clin Nutr.
1999;70:574-575.
Messina M, Bennink M. Soyfoods, isoflavones and risk of
colonic cancer: a review of the in vitro and in vivo data. Baillieres Clin Endocrinol Metab.
1998;12:707-728.
Moyad MA. Soy, disease prevention, and prostate cancer. Semin Urol Oncol.
1999;17:97-102.
Nikander E, Kilkkinen A, Metsa-Heikkila M, et al. A randomized
placebo-controlled crossover trial with phytoestrogens in treatment of
menopause in breast cancer patients. Obstet Gynecol.
2003;101:1213-1220.
PDR. Soy Isoflavones. Accessed at:
http://www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/soy_0238.shtml
on June 10, 2008.
Pendleton JM, Tan WW, Anai S, Chang M, Hou W, Shiverick KT,
Rosser CJ. Phase II trial of isoflavone in prostate-specific antigen
recurrent prostate cancer after previous local therapy. BMC Cancer.
2008;8:132.
Quella SK, Loprinzi CL, Barton DL, et al. Evaluation of soy
phytoestrogens for the treatment of hot flashes in breast cancer
survivors: A North Central Cancer Treatment Group Trial. J Clin Oncol.
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Memorial Sloan-Kettering Cancer Center. Soy. Accessed at:
www.mskcc.org/mskcc/html/69383.cfm on June 10, 2008.
Schröder FH, Roobol MJ, Boeve ER, et al. Randomized,
double-blind, placebo-controlled crossover study in men with prostate
cancer and rising PSA: effectiveness of a dietary supplement. European Urology.
2005; 48:922-930.
Thanos J, Cotterchio M, Boucher BA, Kreiger N, Thompson LU.
Adolescent dietary phytoestrogen intake and breast cancer risk
(Canada). Cancer Causes
Control. 2006;17:1253-1261.
US Food and Drug Administration. FDA Talk Paper: FDA approves
new health claim for soy protein and coronary heart disease. Rockville,
Md: National Press Office; October 20,1999. Talk Paper T99-48.
Van Patten CL, Olivotto IA, Chambers GK, et al. Effect of soy
phytoestrogens on hot flashes in postmenopausal women with breast
cancer: a randomized, controlled clinical trial. J Clin Oncol.
2002;20:1449-1455.
Wu AH, Wan P, Hankin J, Tseng CC, Yu MC, Pike MC. Adolescent
and adult soy intake and risk of breast cancer in Asian-Americans. Carcinogenesis.
2002;23:1491-1496.
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.
Last Medical Review: 11/01/2008
Last Revised: 11/01/2008
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