Nutritional value
Soy is a leguminous plant characterized by
its high content of proteins and by its nutritional
quality. Due to its chemical composition, it is placed
between the legumes and the oleaginous because it has
more proteins (40%) than the other legumes but less
fat (21%) than the other oleaginous seeds.
Soy is a good resource to complement our meals since
it has a high nutritional value that contributes to
achieve a varied, complete and nutritive diet.
There is a growing interest in the food uses of soy
due to the high biological value of its proteins, the
great proportion of polyunsaturated fatty acids of
its lipids, and the versatility of its food use.
Soy and the products derived from it are placed among
the main sources of proteins since as they have fat
of vegetable origin, they constitute a protective food
product. Among other benefits the proteins of soy have
proved to reduce (in various studies) the blood cholesterol
level, opposite effect to the one produced by the protein
products from animals.
The lipids of soy are composed of fatty acids among
which we identify oleic, linoleic, and linolenic acid.
Besides soy has phospholipids such as lecithin, an
important emulsionant that helps in the fat absorption.
Soy is also a good source of the B Vitamins Complex
(Thiamine, Niacin, Piridoxine, and folic acid). As
any vegetable food, soy is obviously free from cholesterol,
while all other sources of animal protein contain it.
50% of its carbohydrates are oligosaccharids (unassimilable
sugars of low glucoforming power) and the other 50%
correspond to dietary fiber, important for weight-reducing
diets. Since it doesn’t contain starch or lactose
(main milk glucid) soy is recommended for people intolerant
to this last substance.
A lot of research done at nutritional levels in the
last years has revealed not only the high nutritional
value of soy (due to its composition of macronutrients)
but also the great amount of health benefits produced
by certain substances contained in it.
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Protein Quality
Proteins are one of the essential nutrients in our
meals since they provide the essential amino acids
to our organism. The quality of a protein is established
according to its content of essential amino acids and
to their availability after being digested.
What is important regarding the protein of soy is that
it contains the nine essential amino acids and a great
part of the no-essential amino acids, thus resembling
and in some cases surpassing the protein of animal
food products
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Soy and essential
amino acids
At the beginning of the 90s, the FDA (Food and Drug Administration), as well
as the Food and Agriculture Organization (FAO) and the World Health Organization
(WHO), established the PDCAAS method (Protein Digestibility-Corrected Amino Acid
Score) to evaluate the quality of proteins. This method determines the quality
of the protein under study according to its profile of amino acids compared to
the requirement in human beings. The proteins that after being evaluated by this
method provide an equal or higher quantity of amino acids with regard to the
requirement already mentioned have a PDCAAS equal to 1. This value means that
when it is consumed as the only source of proteins it can fulfil the recommended
protein requirement for children older than 2 years old and adults. This is the
case of the protein of soy that has a score of 1.
Before, when the biological method PER (Protein Efficiency Ratio) was used to
evaluate the quality of proteins, the protein of soy was considered to be of
lower quality than the protein of animal origin. This was due to the fact that
laboratory animals require a greater amount of methionine than human beings.
The WHO established that the protein of soy contains all the essential amino
acids in adequate amount to suit the protein requirements when it is consumed
in quantities according to age and biological needs.
If we take the FAO Protein as our pattern, the chemical index values of soy (adequately
inactivated) are of 100, just like eggs or meat, as you can see in the following
chart:
| Histidine |
28 |
19 |
| Isoleucine |
50 |
28 |
| Leucine |
85 |
66 |
| Lysine |
70 |
58 |
| Methionine + Cysteine |
28 |
25 |
| Phenylalanine + Tyrosine |
88 |
63 |
| Threonine |
42 |
34 |
| Tryptophan |
14 |
11 |
| Valine |
53 |
15 |
| Total Essential Amino Acids (without Histidine) |
430 |
320 |
| % of protein |
40 |
|
| Chemical index % (FAO Pattern 85) |
100 |
|
*Soybeans inactivated by heat
Experimental results obtained in the CEMPAM CEIGRA
Source: “Introduction to the Biochemistry and
Technology of Foods” Volume II. J.C.Cheftel and
H. Cheftel. Publishing Company: Acribia. 1976.
This means that the proteins of soy have a particular
profile of amino acids that resembles the pattern of
amino acids recommended by the FAO /WHO for children
from 2 to 5 years old and has a PDCAAS of 1.This is
the highest value for a protein.
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Other nutritive elements
Soy contains a variable proportion of the B Vitamins
Complex, especially Vitamin B1 (Thiamine), B2 (Riboflavin),
Niacin, Folic Acid and minerals such as calcium, phosphorus,
magnesium, iron and zinc.
Therefore, when the food products based on soy are
consumed as part of a mixed diet they contribute to
fulfil the individual’s requirement of minerals
and vitamins.
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Soy isoflavones
In the last years soy and the products derived from
it have received a great deal of attention from researchers
and doctors. Epidemiologist studies show that Asian
people have lower rates of heart disease, osteoporosis,
and certain cancers such as breast, prostate and colon
cancer. In the case of women, it has also been noticed
a lesser incidence of menopausal symptoms.
The fact that Asian people lose this advantage when
they adopt occidental ways of eating has lead researchers
to consider that the cause of that advantageous situation
is the Asian diet.
Phytoestrogen (vegetable estrogen) is the generic name
used to define a kind of compounds that are not steroids.
They can be of vegetable origin or derived from the
metabolism “in vivo” of the precursors
present in the plants ingested by man. Phytoestrogens
help regulate the growth of plants and protect them
from stress and from the harmful effects of the ultraviolet
radiation.
Phytoestrogens are weaker than natural estrogens (their
activity is 1/1000 to 1/100000 of natural estrogens)
and differ noticeably from the environmental synthetic
estrogens because they are easily metabolized, they
are not stored in the body tissue and they circulate
through the organism for a very short time. These compounds
are capable of emulating the effects of estrogens because
their structure is quite similar to that of human estrogens
and thus the organism accepts them as such.
The FDA (Food and Drug Administration) has recently
authorized (in the year 2000) to label the soy extract
with the following sentence: “25 g of soy protein
a day as part of a diet low in saturated fatty acids
and cholesterol can reduce the risk of heart disease”.
The soy and isoflavone food products are receiving
a great deal of attention these days because of their
remarkable role in the prevention and treatment of
certain cancers and osteoporosis. The low death rates
of cancer in Asian countries and the anti-estrogenic effect of isoflavones have produced a series of statements
that consider the soy food products to be nutritious
substances that can reduce the risk of cancer.
The most important research carried out by Anderson
(1) revealed that consuming 17 to 25 g of soy protein
a day can produce a significant effect on the decrease
of the cholesterol levels of the organism. This effect
is produced when the animal protein is substituted
in the diet for the soy protein, or when the soy protein
is just added to the diet. This contributes to the
cholesterol decrease, what represents a decrease in
the risk of developing heart disease.
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Potential mechanism
of protection from cardiovascular disease
The protein of soy and its content of isoflavones have very beneficial effects.
Thorough research has shown that a daily intake of soy is associated with
favorable changes in the lipid concentrations. The meta-analysis carried
out by Anderson (1) and some collaborators expressed it in the following
way:
he results obtained show a:
- 9.3% decrease in the total blood cholesterol
- 12.9%
decrease in the LDL cholesterol
- 10% decrease in
the blood TG
- 2.4% decrease in the HDL cholesterol
values
(1) Meta-analysis (intensive revision of the
whole research) carried out by James Anderson, MD, Professor of Medicine
at the University of Kentucky. Published in 1995 in the New England Journal
of Medicine.
The researches done on the soy protein are
very important as they can be considered a useful
factor in the prevention of heart disease, not only
because of the alteration produced by the concentration
of blood lipoproteins, but also because of the antioxidant
function and favorable effects upon the health of
the vascular endothelia encouraged by isoflavones.
ALL
THESE BENEFITS ARE THE REASON WHY SOY SHOULD
BE ADDED TO OUR FOOD INTAKE. ACCORDING TO THE
RESEARCH DONE ON THE SUBJECT, ONE SHOULD TRY
TO INCORPORATE 25 TO 45 ISOFLAVONES A DAY. |
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