Soy foods, including tofu have been in traditional Chinese diet over
thousands of year, according to Chinese literature. The reduced risk of
chronic disease in Asian population, including metabolic syndrome such as cardiovascular
diseases, obesity and diabetes and lesser menopause symptoms in advanced
age, may be aided by eating a lot of soy food accompanied with large
portion of vegetables and fruits. Indeed, according to the study, only
10% of women in the East are experience symptoms of menopause in
advanced age compared to over 70% of their Western counterparts.
According to Dr. Mark Messina, Ph.D., Soy foods contributed from 6.5%8
to 12.8%7 of total protein intake in older adult in Japan.(b)
The approval of cardiovascular benefit of soy by FDA in 1999 accompanied
with the discovery of health benefits in clinical studies over past
decade, prompted the promotion and advertisement of soy's health
benefits in every aspect in Western society. Evidences could be seen by
walking through the supermarkets and drug stores. Soy supplements and
products such as tofu, soy milk, soy-based infant formula, and meatless
“texturized vegetable protein” burgers were widely available. According
to the United Soybean Board’s 2004–2005, 25% of Americans consumed soy
foods or beverages at least once per week, and 74% viewed soy products as
healthy.
Today, the promotion of soy is no longer existed, it may be results of
discovery of adverse effects in single ingredient and animal studies, as
intake of soy is associated to induce risk of certain mammary cancers and
infertility. The publication of the result have drawn many criticisms.
According to Thomas Badger, director and senior investigator at the
Arkansas Children’s Nutrition Center in Little Rock, these effects are
seen only under certain experimental conditions that are not likely to
occur in humans—and therein lies the crux of the debate(a). Equol
(4',7-isoflavandiol), an isoflavandiol metabolized from daidzein may be
the causes, as 90% of Eastern population are equol producers but only
30% in the West.
The explanation of the positive effect of soy isoflavones in reduced
risk of mammary cancers by University of Goettingen may be interesting,
as researchers said" Most importantly, there is dispute as to whether
isoflavones derived from soy or red clover have negative, positive or any effect at all on the mammary gland or endometrium. It is beyond any doubt that soy products may have cancer
preventing properties in a variety of organs including the mammary
gland. However, these properties may only be exerted if the developing
organ was under the influence of isoflavones during childhood and
puberty".
Soybean is genus Glycine, the family Fabaceae, one of the legumes that
contains twice as much protein per acre as any other major vegetable or
grain crop, native to Southeast Asia. Now, it is grown worldwide with
suitable climate for commercial profits.
Nutrients
1. Carbohydrates
2. Dietary fiber
3. Fat
4. Protein
5. Essential amino acid
6. Vitamin A
7. Vitamin B6
8. Vitamin B12
9. Vitamin C
10. Vitamin K
11. Calcium
12. Iron
13. Magnesium
14. Phosphorus
15. Potassium
16. Sodium
17. Zinc
18. Etc.
Phytochemicals
1. Isoflavones
2. Genistein
3. Saponins
4. Beta-sitosterol
5. Daidzein
I. Soy in Eastern population
A. The Japanese population
Japan, an island nation in the Pacific Ocean, lies to the east of the
Sea of Japan, China, North Korea, South Korea and Russia, stretching
from the Sea of Okhotsk in the north to the East China Sea and Taiwan in
the south(1). According to Moriyama, Japanese women and men live longer
and healthier than everyone else on Earth, it may be result of
healthier Japanese diet and lifestyle. According to the World Health
Organization, the Japanese have an average of 75 years healthy
living with disability-free, it may be due to average soy intake 10 to
70 times higher than in Western
people(1a)(1b)
A.1. Soy and the risk of cerebral infarction (CI) and myocardial infarction (MI) in Japan population
The searching of the Keywords in PubMed, soy and heart diseases and
stroke in Japan found 3 studies, all showed the positive effect of soy
in reduced risk heart disease and stroke.
Cerebral infarction (CI) is defined as a type of ischemic stroke due to
blockage in the blood vessels supplying blood to the brain.
Myocardial infarction (MI) is also known as heart attack. It is defined
as a condition of blood stop flowing properly to part of the heart as a
result of not receiving enough oxygen.
According to National Cardiovascular Center, Japan, the studied 40,462
Japanese (40 to 59 years old, without cardiovascular disease or cancer
at baseline), yields interest results.
People who consume more soy are less likely to be current smokers but
more likely to be hypertensive, with men are more
likely to have diabetes mellitus. The frequency of soy intake was
positively related to daily intake of rice, vegetables, fruits, fish,
potassium, calcium, carbohydrate, polyunsaturated fatty acid, saturated
fatty acid, fiber, and isoflavones for both
sexes.
The study started in the 1990 with food-frequency questionnaire included
44 foods with 3 questions to assess soy, bean, and miso consumption.
The 1995 follow-up questionnaire covered 147
foods with 8 questions on soy products.
The result is astonishing, during a follow-up period that averaged 12.5
years, 1230 strokes were documented, of which 1137 were confirmed
through imaging or autopsy. eventhrough high isoflavone
intake was associated with reduced risk of CI and MI in middle-aged
Japanese subjects, but not in men and dietary
isoflavones and may be beneficial to
postmenopausal women for the prevention of ischemic CVD(2). Intake of
miso soup showed to reduce risk of hypertension but did not
contributed to ischemic CVD mortality in neither men or women.
Strong evidences of epidemiological studies from the East and West have
shown that hyperlipidemia is a major risk factor in contribution to
heart diseases, notably on intermediate end points(3)(4). Soy foods
intake has been known to contain lowering cholesterol and blood pressure
effects. According to the Veterans Affairs Medical Center, daily soy
protein showed a significantly decreased serum concentrations of total
cholesterol, LDL cholesterol, and triglycerides without significantly
affecting serum HDL cholesterol concentrations.(4). But the study
suggested that the mechanism of reduced risk of cerebral infarction
(CI) and myocardial infarction (MI) for postmenopausal Japanese women
may not be through reduction of lipid profile but
through exposure to a large quantity of isoflavones, which act as
estrogen agonist because estrogen receptors are not occupied with plasma
estradiol in postmenopausal women.
In case of hypertension in the subject of study, although the disease
have been shown to contribute to the early risk factor for the
progression heat disease and stroke(6)(7)(8)(9). Consumption of soy has
no effect in reduce risk of the development of cerebral infarction (CI)
and myocardial infarction for people with histories of hypertension
and diabetes mellitus and medication use for
hypercholesterolemia, even soy has shown effectively in reduced high
blood pressure(12)
In support to the above, the dietary intervention study targeting female students by using cake
containing soybean protein and isoflavone at the Mukogawa Women's
University, 4 weeks dietary intake of soy
protein found to reduce CHD risk among Japanese female students with a
high plasma cholesterol level(10) and Dr. Nagata C. at the Gifu
University School of Medicine, Gifu, Japan, in the study of association between soy product intake and mortality from cancer and heart disease in Japan, suggested that soy foods intake showed a preventive role in against stomach cancer and heart disease death(11).
Dr. Yoshihiro Kokubo and the research team also acknowledged the
limitation of the study such as ethic group, measurement errors with
nutrient intake or due to it self report, but insisted that nationwide
annual health screenings may ease the self report concern.
They also clarified that the result of the study of dietary intake of
isoflavones, are not relevant to the association of isoflavone
supplement use with ischemic CVD.
In deed, the effectiveness of soy isoflavone in reduced risk of cerebral
infarction (CI) and myocardial infarction in this case, yields some
questions due to it ethnicity.
a. If soy is found to be effective in reduce risk of hypertension and
hyperlipidemia, why it does not contribute to the reduce risk of
cerebral infarction (CI) and myocardial infarction in men with histories
of hypertension and diabetes mellitus and
medication use for hypercholesterolemia.
Would the medication be the cause? As epidemiological study insisted
the lowering effect of blood pressure and cholesterol are associated to
reduce risk heart disease and stroke.
b. Although soy isoflavone showed an effectiveness in reduce risk of
cerebral infarction (CI) and myocardial infarction and mortality, would
dietary with high in fruit and vegetable also best known for the reduce
risk of heart disease and stroke be also taken into account?
c. The effectiveness of the study may only be true for equol producers population as 90% of subjects' study are equol producers?
d. Would the "Japanese Phenomenon" interfere with the study, as administration of isoflavone "inexperienced" women
at the time of menopause, the phytoestrogens appear to share the same
effects as estrogen used in classical preparations for hormone
replacement therapy?
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References
(a) The Science of Soy: What Do We Really Know? by Julia R. Barrett
(b) Guideline for healthy soy intake(the Unite Soybean board)
(1) Japan, Wikipedia
(1a) Erdman JW Jr. AHA Science Advisory: soy protein and cardiovascular
disease: a statement for healthcare professionals from the Nutrition
Committee of the AHA. Circulation. 2000; 102: 2555–2559
(Soy protein and cardiovascular disease)
(1b) van der Schouw YT, Kreijkamp-Kaspers S, Peeters PH, Keinan-Boker L,
Rimm EB, Grobbee DE. Prospective study on usual dietary phytoestrogen
intake and cardiovascular disease risk in Western women. Circulation.
2005; 111: 465–471(Cardiovascular diseases in women)
(5) Soy intake and breast cancer risk: an evaluation based on a systematic review of epidemiologic evidence among the Japanese population by Nagata C1, Mizoue T, Tanaka K, Tsuji I, Tamakoshi A, Matsuo K, Wakai K, Inoue M, Tsugane S, Sasazuki S; Research Group for the Development and Evaluation of Cancer Prevention Strategies in Japan.(PubMed)
(6) Probiotic Beverage with Soy Isoflavone Consumption for Breast Cancer Prevention: A Case-control Study by Toi M1,
Hirota S, Tomotaki A, Sato N, Hozumi Y, Anan K, Nagashima T, Tokuda Y,
Masuda N, Ohsumi S, Ohno S, Takahashi M, Hayashi H, Yamamoto S, Ohashi
Y.(PubMed)
(7) Associations of intakes of fat, dietary fiber, soy isoflavones, and alcohol with levels of sex hormones and prolactin in premenopausal Japanese women by Tsuji M1, Tamai Y, Wada K, Nakamura K, Hayashi M, Takeda N, Yasuda K, Nagata C.(PubMed)
(8) Plasma isoflavone level and subsequent risk of breast cancer among Japanese women: a nested case-control study from the Japan Public Health Center-based prospective study group by Iwasaki M1, Inoue M, Otani T, Sasazuki S, Kurahashi N, Miura T, Yamamoto S, Tsugane S; Japan Public Health Center-based prospective study group.(PubMed)
(9) Isoflavones--safe food additives or dangerous drugs? by Wuttke W1, Jarry H, Seidlová-Wuttke D.(PubMed)
(10) Effect of a soybean product on serum lipid levels in female university students by Takahashi K1, Kamada Y, Hiraoka-Yamamoto J, Mori M, Nagata R, Hashimoto K, Aizawa T, Matsuda K, Kometani T, Ikeda K, Yamori Y.(PubMed)
(11) Ecological study of the association between soy product intake and mortality from cancer and heart disease in Japan by Nagata C.(PubMed)
(12) Association of blood pressure with intake of soy products and other food groups in Japanese men and women by Nagata C1, Shimizu H, Takami R, Hayashi M, Takeda N, Yasuda K.(PubMed)
(13) Effects of dietary intake of soy protein and isoflavones on cardiovascular disease risk factors in high risk, middle-aged men in Scotland by Sagara M1, Kanda T, NJelekera M, Teramoto T, Armitage L, Birt N, Birt C, Yamori Y.(PubMed)
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