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Multi-Systemic Benefits of Soy

By Yousry Naguib, PhD .

SIE (Supplement Industry Executive)


Soy foods and certain soy constituents, particularly
isoflavones, are becoming of increasing interest as nutritional

agents. Research studies have shown that soy may have a
positive effect on everything from menopausal symptoms to
cancer, osteoporosis and heart disease. In 1999, the U.S.
Food and Drug Administration (FDA) announced that eating 25
grams of soy protein a day lowers the risk of coronary heart
disease, and ruled that any food containing at least 6.25 grams
of soy protein per serving can carry a "healthy heart" label.

Chinese and Japanese, who for thousands of years used
soybeans as a source of nutrition, have recognized the
medicinal values of soybeans. Samuel Bowen introduced the
soy plant from China to the American colonies in 1765. Large-
scale production of soybeans in the U.S. began during the
1850s. In 1999, farmers planted soybeans on 72 million acres,
amounting to 27 percent of the total crop area in the U.S.
Soybeans are an economically important crop, valued at

approximately $15 billion annually, which serves as a source of
protein for animals and humans.

Consumption of soy foods is increasing because of beneficial
effects on health, which include lowering of plasma cholesterol
and reducing the risk of heart disease, as well as prevention of
cancer.

Soybeans and their products are consumed by humans in a
variety of forms, including whole soybeans, tofu, and soymilk.
Soy protein can be isolated from the whole bean for
consumption through processing.

Soy is also rich in bioactive isoflavones, of which daidzein,
genistein and glycitein are the main components. These sugar
free (aglycon) isoflavones occur in soybeans in the glycosidic

(glycone) form, meaning it is bound to a sugar molecule, and is
referred to as daidzin, genistin, and glycitin. Isolated soy
protein contains up to 50 percent of isoflavones found in
unprocessed beans. The amount of the isoflavone genistein in

most soy products ranges from 1 to 2 mg per g protein.

These phytoestrogenic isoflavones mimic estrogen and hence
they are capable of alleviating postmenopausal symptoms. The
anti-estrogenic effects of these isoflavones are ascribed to

their ability to bind estrogen receptor sites thereby making the
receptors unavailable for binding by the natural, more potent
estrogens of the body.

Bioavailability
In one human study, ingestion of 40 g of isoflavone-rich
vegetables for a period of five days significantly raised (1,000
times) the amount of isoflavones in the urine. Research also

showed that the bioavailability of isoflavones depends on the
efficiency of gut microflora to metabolize the glycosidic
isoflavones. These isoflavones are first cleaved in the gut, and
then absorbed into the blood.

Although most soy isoflavone products are sold in the glycon
form, there are some unique products that supply isoflavones
in the aglycon form. Hydrolyzing the isoflavone glycone frees

up the bioavailable isoflavone from the sugar moiety.

Clinical studies examining the efficacy of isoflavones
supplements must be carefully designed so as to rule out
effects attributable to isoflavones in the diet, which may lead to
false conclusions.

Cancer Prevention
Epidemiological studies have indicated that high dietary intake

of soybeans by Chinese and Japanese is associated with
lower incidence of cancers, particularly cancers of the breast
and prostate. The consumption of soy has also been indicated
in the prevention of colorectal, lung, and gastric cancers.

The incidence rates of breast and prostate cancers are high in
Western countries, such as the U.S., where consumption of
soy foods is low as compared to Eastern countries. Asians

consume about 10 to 35 g of soy foods daily per capita, which
translates to a daily dose of 25 to 100 mg isoflavones.
Conversely, Americans and Western populations ingest only a
few milligrams or less of isoflavones per day. A recent survey
showed the average intake of total isoflavones to be 15 mg per
day, which is broken down to 7 mg genistein, 6 mg daidzein,
and 2 mg glycitein.

The isoflavones genistein, daidzein, and glycitein in soy
products have been shown to exhibit anticancer effects.
Genistein has been recognized as the most potent of these
compounds in inhibiting various processes in the development

of cancer including cell proliferation and transformation. For
example, genistein has been found to inhibit the process of
angiogenesis (the process of growth of new blood vessels into
tissue) involved in the development of tumors. Genistein has
also been shown to decrease the amount of reactive oxygen

species produced by tumor cells.

Because of the similar chemical structure of these isoflavones
and the hormone estradiol, it was hypothesized that these
compounds may be related to the risk of breast cancer.
However, a recent study showed that individuals with the
highest levels of daidzein, glycitein and total isoflavonoids in
their urine samples had about half the cancer risk than those

with the lowest isoflavones levels. The study concluded that
high intake of soy foods may reduce the risk of breast cancer.

Clinical studies also appear to support these epidemiological
observations. In a case-control study, women with newly
diagnosed early breast cancer with a high intake of isoflavones
had a substantial reduction in breast cancer risk.

A recent review published in Journal of Nutrition also reported
that isoflavone supplements do not affect breast tissue density
in pre-menopausal women and may decrease density in
postmenopausal women. These effects are opposite to those
of hormone replacement therapy. The study suggested that
breast cancer patients might benefit from soy products.

In a recent study, pre-menopausal women between the ages of
25 and 55 years, free of breast cancer, were randomly

assigned to receive either a dietary supplement of isoflavones
(40 mg per day) or a placebo for 12 weeks. The hormone
estradiol and its metabolite estrone (anticipated to be a
carcinogen) decreased significantly in the isoflavone-group as
compared to the placebo. The study suggested that increased
isoflavone intake affects estrogen metabolism, thereby
demonstrating a potential to reduce the risk for breast cancer.

Cardiovascular Support
Elevated plasma levels of low-density lipoprotein (LDL) and
triglycerides present a risk for cardiovascular disease.
Consumption of plant proteins, such as soy, often results in
significant lowering of LDL and total cholesterol levels.
Research showed that rats fed soy-based diets had lower
serum cholesterol levels than those on a casein diet (animal
protein). It was hypothesized that the cholesterol-lowering

effect of soy protein is due to its ability to modulate LDL
receptor levels in the liver.

Studies have also demonstrated the ability of soy to lower total

cholesterol and low-density lipoprotein (bad cholesterol) levels
in humans. On the basis of a food-frequency questionnaire
given to 4899 Japanese men and women, researchers noted
decreasing plasma levels of cholesterol with increasing
consumption of soy products.


Researchers also investigated the role of soy isoflavones on
the risk of cardiovascular disease and menopausal symptoms
in women consuming soy-based diets, and noted significant
improvement in lipid and lipoprotein levels, and blood pressure
symptoms.

A double-blind study suggests that even partial replacement of

animal protein with a soy protein was effective in lowering of
plasma cholesterol in 21 severely hyper-cholesterolemic
patients.

Soy isoflavones have been suggested to have a role in
coronary heart disease prevention. Consumption of a high-
isoflavone soy diet (128.7 mg/day) by pre-menopausal women
for three menstrual cycles lowered LDL cholesterol by 7.6 to 10

percent.

The health benefit of soy products in the cardiovascular area
stems from their ability to lower total cholesterol and LDL-
cholesterol, to reduce their susceptibility to oxidation, and to
inhibit platelet aggregation.

Bone Health
Soy isoflavones have also been found to promote healthy

bones. Although calcium is the primary dietary factor that
dictates the course of osteoporosis, other variables, including
estrogen deficiency, exercise and protein composition of the
diet, come into play to influence the overall maintenance of
healthy bones. Diminished level of estrogens due to
menopause, lack of exercise, and excessive protein intake all
exert deleterious effects on bone integrity. To reduce these
negative effects, the use of soy protein in combination with

calcium has been suggested as an advantages way of
promoting calcium uptake and bone strength.

Analysis of data from a study of women aged 42 to 52 years
revealed that pre-menopausal Japanese women whose dietary
soy isoflavones intakes were high had high spine and femoral
neck body mineral density.

Women's Health Issues
Currently, there is an interest among postmenopausal women
to treat problems associated with menopause, such as hot
flashes, with natural products as opposed to synthetic estrogen

drugs. Indeed, clinical research showed isoflavones reduced
the incidence of hot flashes in menopausal women. These
compounds may be designated as healthy alternatives to
hormone replacement therapy.

A Japanese study on 284 women aged 40 to 59 years showed
that consumption of fermented soy products significantly
reduced hot flushes as compared to the control group.

In a double-blind, randomized study, postmenopausal women
given 400 mg per day of a standardized soy extract
(Soyselect), corresponding to 50 mg per day of isoflavones for
six weeks showed a significant reduction in the number of hot

flashes per week. The study concluded that Soyselect is safe
and efficacious in relieving hot flashes in women who seek
alternatives to hormone replacement therapy.

Apparently, too much of a good thing could be harmful, so one
needs to have a balanced intake of soy products and soy
supplements. A study published in the April issue of the
Journal of the American College of Nutrition presented

evidence that the brains of elderly people who ate tofu at least
twice a week for 30 years were aging faster than normal. The
estrogen-like substances in soy may also dampen the function
of the thyroid. A study found that after consuming 40 mg of
isoflavones for a few weeks, women experienced fatigue, and
overall body aches. Some women gained weight and reported
heavier menstrual periods.

Summary
Soy products have long proven to be effective in Asian
cultures, and are now becoming popular, both for men and
women's health benefits. Soy proteins and isoflavones have
been shown in various studies to combat cancer, osteoporosis,
menopausal symptoms, gastrointestinal disorders, and
cardiovascular diseases. SIE

 

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