Ăn Đậu Nành Và Sản Phẩm Đậu Nành Lợi Hại Ra Sao ?



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Cancer
Allegation:
The argument has been put forth that the phytoestrogens (plant estrogens) contained in soy promote the growth of cancers.

Reality:
While a few studies have found that animals who are implanted with cancer cells and then fed soy protein isolates show increased growth of the cancer cells, the majority of the research shows soy to have an inhibitory effect on cancer growth. A recent meta-analysis of the literature relating to soy and cancers of the breast, colon, and prostate, found that individuals who consumed soy had a reduced risk of developing all three of these types of cancers [5].

When results are not in favor of their conclusion, the opponents of soy often call into question the research method used. Meta-analyses have been questioned as a less than valid research method. SOS has stated in their Marketplace Newsletter that meta-analyses are, “a method upon which many in the scientific community frown.”

This same newsletter also claims that meta-analyses that show benefits to consuming soy are flawed because, “there is also the added temptation for researchers, particularly those funded by industry, to omit studies that prevent desired conclusions.” Omission of studies that find the opposite of what one has already concluded is certainly a significant flaw and the conclusions drawn by meta-analyses are appreciably dependent upon proper use of the research tool. A meta-analysis involves conducting a systematic review of the research on a particular topic. If one uses a narrative approach rather than a systematic approach, that is picks and chooses which studies to include based upon personal bias, there is plenty of room for inaccurate conclusions. The key words here being systematic (an organized, unbiased synthesis of the data) versus narrative (an account based upon personal selection).

In fact, properly conducted meta-analyses are one of the more powerful statistical tools for assessing the effect of health interventions and are not “frowned upon” by any scientific community with which I am familiar. The meta-analysis, to which I referred, above, was systematically conducted and showed no apparent bias.

With that aside in mind, women may want to exercise some caution if they have a history of estrogen dependent breast-cancer. While there is no definite proof that consumption of phytoestrogens increases the risk of a reoccurrence, and some studies even show a reduction in risk of reoccurrence, the jury is still out in this area. There is some indication that consumption of soy isoflavones may interact with the anti-breast cancer drug, tamoxifen, reducing its efficacy [6]. While this effect is not certain, it would be wise to discuss your consumption of soy products with your doctor if you have a history of breast cancer.

The most logical course to take if one is concerned about the possible negative effects of plant estrogens contained in soy is to avoid consuming highly processed forms of soy, or reduce consumption of those products. It has been suggested by a few scientists that the degree of processing effects how soy phytoestrogens will react with the human body, with the more highly processed soy products (especially soy protein isolates) exerting a more estrogenic effect in the body. Just to put this in perspective, some of the same researchers who have found estrogenic effects on animals when feeding them high concentrations of soy protein isolates, have also found similar estrogenic effects for isolates of other plants – namely cabbage and brussel sprouts [7]. No one is suggesting that we all stop eating cabbage because it obviously offers significantly more benefits than it does risks. We just generally do not eat extracts of freeze-dried cruciferous vegetables. The same should hold true for soy and any other food – the closer to its whole form as possible is probably the best choice.



Brain Health
Allegation:
Soy causes Alzheimer’s disease, dementia, and reduced brain functioning.

Reality:
The great majority of the research relating to soy consumption and brain health shows soy to have a protective effect on the brain, not a damaging effect on the brain. One article that has frequently been cited as “proof” that soy damages the brain found some possible benefits and some possible harm for male rats fed a diet high in phytoestrogens [8]. The researchers who conducted this study have also conducted a number of other studies wherein the conclusions were that soy phytoestrogens are protective to the brain.

Edwin Lephart, the lead researcher on the above noted study, has this to say in response to his article being cited as proof of soy causing neurodegeneration of the brain: “In general, phytoestrogens, and more specifically isoflavones, appear to be neuroprotective. Meaning these molecules protect the brain cells and brain function. The research that you state via the Price foundation citing our article is but one study. There are many studies and many molecules that isoflavones influence in the brain and when one examines the overall effect of isoflavones the current evaluation, in my opinion, is that phytoestrogens derived from soy are neuroprotective. [9]”



Thyroid Health
Allegation:
Soy consumption reduces thyroid function and/or causes thyroid cancer.

Reality:
Some older studies of infants fed soy-based formula not fortified with iodine showed reduced thyroid functioning in those infants. Further research has shown that, in the absence of an iodine deficiency, soy does not reduce thyroid function [10]. In relation to infants with congenital hypothyroidism, there is not yet complete consensus amongst the scientific community as to whether soy formula complicates this pre-existing condition. If you have an infant with congenital hypothyroidism, again, soliciting the advice of your doctor or health care provider would be a wise decision.

As far as thyroid cancer is concerned, large population-based studies show that soy not only does not increase the risk of thyroid cancer, it exerts a protective effect [11].



Infertility and reproductive health
Allegation:
Soy causes infertility, hormonal imbalances, hypospadias, and desmasculinization of males.

Reality:
A few studies of the offspring of rodents who were fed soy isolates during pregnancy and lactation and rodents who were injected with soy isoflavones in infancy have found evidence of negative reproductive outcomes. However, there is a significant difference in the amount of estrogen to which fetal rats and fetal humans are normally exposed. Fetal rats are normally exposed to very small quantities of estrogen in utero whereas human fetuses are normally exposed to large quantities of estrogen in utero – this is without any soy consumption on the mother’s part. It has been suggested that rats, unlike humans, are not meant to be exposed to significant quantities of estrogen in utero and their reproductive organs are, therefore, more biologically sensitive to the effects of isoflavones. [12]

Whatever the mechanism for the poor outcomes for the rodents, these results have not been replicated in humans. In fact, research on human infants exposed to soy in utero and during infancy has found no statistically significant differences in sexual development or reproductive health other than one study that found slightly longer menstrual periods in women who were fed soy formula as infants [12]. Clinical studies of infants fed soy formula, arguably the infants with the highest exposure to soy, have found no hormonal defects, no increase in infertility and normal sexual maturation. [13] [14] [15] [16]

The one human study that implicated a vegetarian diet during pregnancy as a cause of hypospadias [17] (a congenital defect of the male genitalia in which the opening is not at the tip of the penis) should not be entirely dismissed, but is certainly not conclusive either. The researchers followed a large cohort of pregnant women in Britain and looked at many factors that could influence the development of hypospadias, including maternal diet. They then followed up to determine which factors were associated with a greater instance of hypospadias. Among those factors considered, the only ones that increased the risk of having a male child born with this defect were iron supplementation during pregnancy, being vegetarian during the pregnancy, and/or influenza during the first trimester.

Without looking any further, these findings may be alarming. However, we need to consider what aspect of their environment may have increased the instance of hypospadias among the boys born to the vegetarian mothers – soy is certainly not the only possibility and perhaps not even the most logical suspect once the remainder of the findings are considered. The researchers do hypothesize in the abstract of their article that “vegetarians have greater exposure to phytoestrogens than do omnivores, these results support the possibility that phytoestrogens have a deleterious effect on the developing male reproductive system. [18]”

We must understand that a hypothesis is only a tentative explanation and not a tested theory. Yes, it is possible that phytoestrogens played a role, but it is also possible that the pesticides on the larger quantities of produce eaten by the vegetarian women played a role, another hypothesis that the researchers offer in this paper. (Very few of the women in the study ate organic produce. Of those who did, none had a son born with hypospadias, but the numbers of women who fell into this category – consuming only organic produce – was so small that it was not possible to calculate if the protective effect of organic produce was statistically significant.)

Again, if we bothered to read the entire article, we would find the statement that, “the association of hypospadias with a vegetarian diet was not obviously explicable by the components of a vegetarian diet. There were differences in the proportion of hypospadias cases born to mothers consuming soya milk or other products, but they were not significant, possibly because there were too few mothers who reported consuming such foods. [19]” [Emphasis mine] Thus, there was an association with being vegetarian during pregnancy and increased risk in having a son born with hypospadias, but there was not an increase in risk related to consuming the two soy products that the dietary questionnaire accounted for: soy milk and soy “meats.”

Without a more thorough analysis of the dietary habits of pregnant women, it is impossible to determine if soy was the cause of the increased incidence of hypospadias among the vegetarian women included in this study or if there was some other dietary or other environmental cause. Further research is warranted, but until these findings are replicated with a more careful dietary analysis, we really do not know what caused the increase in hypospadias in the infants in the study.

Soy Formula
Then we have the issue of soy formula. The feeding of soy-based formula to infants is highly contentious. All doctors, scientists and health professionals with whom I spoke (myself included) would recommend breast feeding over any kind of formula when at all possible. With that aside, it is hard to determine the true effects of soy formula on human infants because so few studies have been done on human infants. The Arkansas Children’s Nutrition Center based at the University of Arkansas for Medical Sciences (UAMS) has a research team who is in the process of conducting the largest and most complete study to date of infants fed soy formula, cow’s milk formula and human breast milk. The lead researcher for this study, Tom Badger, was kind enough to answer some questions for me via email and to speak with me on the phone.

Dr. Badger stated that the number of children fed soy formula in the U.S. is larger than in any other nation (25% of the four million infants born in the U.S. each year are fed soy-based formula). This sets the U.S. up as the perfect location for testing the long-term effects of this feeding choice. Dr. Badger estimates that 1 million infants are fed soy formula each year in the U.S. and “thus, we have a lot of experience with this food source for infants… These children grow and develop normally and have disease and disorder rates equal to those of infants fed milk-based formula. All of our research thus far suggests that there are health benefits rather than adverse effects of consuming soy formula. Therefore, any adverse effects would need to be very subtle or occur much later in life, say after age 40-45 years. [20]”

The Arkansas study currently has hundreds of children enrolled with more children being enrolled every week. The oldest children in the study are three years old at this point and have been followed since four weeks of age. The children in the study are seen every month for the first year of life with each visit lasting between two to six hours. The study participants are seen yearly thereafter until age six, with the hopes that funding will be extended to allow the children to be followed through puberty. Thus far, all evidence from this study (which includes body composition, brain growth and function, endocrinology, and metabolism) shows no difference in the children fed soy-based formula versus cow’s milk-based formula.

Dr. Badger’s team did an in-depth review of prior studies that showed adverse effects on young animals who were injected with or fed soy derivatives. They spoke with the researchers of those studies and concluded that there were major flaws in the studies and/or there were other factors that made the studies inapplicable to human infants. Dr. Badger did note that animal studies are not always flawed by virtue of the fact that they were done on non-human animals and the flaws found varied depending on the studies.



Animal Studies
In general, the concern with the animals studies that relate to isoflavones fall into a few areas. One concern is that many of the studies that found increases in cancer dealt with immunocompromised animals and/or female animals whose ovaries and uteruses had been removed. An average adult or child has not had a complete ovo-hysterectomy nor is s/he immunocompromised. It is not possible to generalize to a whole population based upon a small component of that population with different circumstances.

Also, some animal models inject purified isoflavones into rats. Isoflavones found in soy are bound into a completely different form in the whole food (soy milk and tofu are included in this discussion as “whole foods” as the processing involved – heat from cooking and blending of the whole soybeans with water and coagulants – does not turn them into purified isoflavones). Soy consumed as a whole food, including soy milk, tofu and fermented soy products, must be metabolized in order to extract the isoflavones. Feeding or injecting an animal with purified isoflavones skips over this metabolic process and is basically the same as giving the animal high doses of a drug.

Unfortunately, animal studies that include feeding soy products (not just purified isoflavones) cannot always be easily translated into human effects either. For instance, studies that have found reduced testosterone levels in male monkeys fed soy formula, failed to take into account the different intestinal bacteria found in monkeys that are not found in humans. Despite our close genetic relation, monkeys have bacteria in their intestines that metabolizes daidzein (a soy isoflavone) into a highly estrogenic substance; humans do not have this same bacteria.

The animal models can be a good place to start, but should not be relied upon for making health decisions for humans without replication in human subjects. At this point, those studies that have been conducted on humans, and even the majority of those conducted on animals, have leaned towards the conclusion that soy is beneficial to health, not detrimental.



What forms of soy and how much soy should you be eating?
Since most of the studies that raise concerns about soy consumption seem to focus on pre-metabolized isolates or other similarly processed forms of soy, the wisest choice to is to choose to eat soy foods as part of a balanced diet and in the least processed form available. Soy can be a valuable source of protein in a vegetarian or vegan diet, but it should not be relied upon as the sole source of protein. We should also be careful with drawing the conclusion that, if a little bit of something is good, a lot must be even better. Variety in your diet is an excellent way to ensure balance and good health.

Choosing traditional and less processed forms of soy (such as tofu, miso, tempeh, edamame and even soy milk) over highly processed soy foods (such as soy cheeses, soy meats, and soy protein isolates) is likely to be a safer choice, as well. We all need our treats sometimes and the research does not support the conclusion that eating a little vegan soy cheese on your pizza is going to cause health problems, so go ahead and allow yourself some indulgences every now and then if you want to. Just don’t make soy cheese and soy sausage casserole the mainstay of your diet.



Footnotes:
1. Setchell KD, et al. Isoflavone content of infant formulas and the metabolic fate of these early phytoestrogens in early life.
Am J Clin Nutr 1998 Dec;68(6 Suppl): 1431S-1435S.
2. Nagate C, et al. Inverse association of replacing meat with soyabean in the diet on sex hormone concentrations in Japanese men.
Nutr Cancer 2000; 36(1): 14-8.
3. Habito RC, et al. Effects of replacing meat with soyabean in the diet on sex hormone concentrations in healthy adult males.
Br J Nutr 2000 Oct;84(4): 557-63.
4. Gradern-Thorpe D, et al. Dietary supplements of soya flour lower serum testosterone concentrations and improve markers of oxidative stress in men.
Eur J Clin Nutr 2003 Jan;57(1): 100-6.
5. Badger TM, et al. Soy Protein Isolate and Protection Against Cancer.
J Am Col Nutr 2005: 245(2): 146S-9S
6. Ju YH, et al. Dietary genistein negates the inhibitory effect of tamoxifen on growth of estrogen-dependent breast cancer (MCF-7) cells implanted in athymic mice.
Cancer Res 2002 May; 62(9): 3474-7.
7. Ju YH, et al. Estrogenic Effect of Extracts from Cabbage, Fermented Cabbage, and Acidified Brussel Sprouts on Growth and Gene Expression of Estrogen-Dependent Human Breast Cancer (MCF-7) Cells.
J Agric Food Chem 2000; 48(10): 4628-34.
8. Lephart, et al. Phytoestrogens decrease brain calcium-binding proteins but do not alter hypothalamic androgen metabolizing enzymes in adult male rats.
Brain Res 2000 Mar 17; 859(1): 123-31.
9. Personal communication, August 2005
10. Bruce B, et al. Isoflavone supplements do not affect thyroid function in iodine-replete postmenopausal women.
J Med Food 2003 Winter; 6(4): 309-16.
11. Haselkorn T, et al. Why Are Thyroid Cancer Rates So High in Southeast Asian Women Living in the United States? The Bay Area Thyroid Cancer Study.
Cancer Epidemiology Biomarkers and Prev 2003 Feb; 12: 144-50.
12. Merritt RJ and Jenks BH. Safety of Soy-based Infant Formulas Containing Isoflavones: The Clinical Evidence.
J Nutr 2004 May; 134: 1220S-4S.
13. Munro IC, et al. Soy Isoflavones: a safety review.
Nutr Rev 2003; 61:1-33.
14. Strom BL, et al. Exposure to soy-based formula in infancy and endocrinological and reproductive outcomes in young adulthood.
J Am Med Assn 2001; 286:807-14
15. Churella HR, et al. Growth and protein status of term infants fed soy protein formulas differing in protein content.
J Am Coll Nutr 1994; 13:262-7.
16. Businco L, et al. No oetrogens hormonal effects in long-term soy formula fed children.
J Allergy Clin Immunol 1999; 103:S169.
17. North K and Golding J. A maternal vegetarian diet in pregnancy is associated with hypospadias. The ALSPAC Study Team. Avon Longitudinal Study of Pregnancy and Childhood.
British J Urology 2000 Jan; 85(1): 107-13.
18. Ibid. Pg. 107
19. Ibid. Pg. 111
20. Personal communication, August 2005

VegFamily Resources: Visit the VegFamily Shopping Guide for vegan products and companies that support VegFamily.

Christa has a Masters degree in Public Health and works part-time as a health educator. She lives in Colorado with her husband and two daughters. Christa has been vegetarian for 20 years and vegan for nearly 17 years.

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Nguồn tài liệu của bài sau đây:

http://www.healingdaily.com/detoxification-diet/soy.htm

Is soy healthy?

Soy is not the health food that you think it is.

From tofu and tacos to baby formula and burgers, soy products have swept the nation as a healthy source of protein, with a reputation for being all natural and good for you. New studies have however raised questions over whether the ingredients in soy might increase the risk of breast cancer in some women, affect brain function in men and lead to hidden developmental ab-normalities in infants.



The core of their concerns rests with the chemical makeup of soy: in addition to all the nutrients and protein, soy contains a natural chemical that mimics estrogen, the female hormone. Some studies in animals show that this chemical can alter sexual development. And in fact, 2 glasses of soy milk/day, over the course of one month, contain enough of the chemical to change the timing of a woman’s menstrual cycle.

Isoflavones in soybeans

Soybeans contain an impressive array of phytochemicals (biologically active components derived from plants), the most interesting of which are known as isoflavones. Isoflavones are the compounds which are being studied in relation to the relief of certain menopausal symptoms, cancer prevention, slowing or reversing osteoporosis and reducing the risk of heart disease.

Soy critics point to the fact that soybeans, as provided by nature, are not suitable for human consumption. Only after fermentation for some time, or extensive processing, including chemical extractions and high temperatures, are the beans, or the soy protein isolate, suitable for digestion when eaten.

Soybeans also reportedly contain an anti-nutrient called "phytic acid", which all beans do. However, soybeans have higher levels of phytic acid than any other legume. Phytic acid may block the absorption of certain minerals, including magnesium, calcium, iron and zinc. Epidemiological studies have shown that people in 3rd World Countries who have high consumption of grains and soy also commonly have deficiencies in these minerals. It must also be noted that this may be of particular concern with regard to babies who are using soy-based infant formulas.



What is the truth when it comes to soy?

So how does one get to the truth when it comes to soy? Usually, the first question I ask is… "Where is the money? Who has something to be gained from one side or the other?" With the soy issue, there does not seem to be an easy answer here either… and that's because there appear to be strong financial incentives on both sides of the argument.

Who has something to gain from the consumption of soy? Perhaps companies like Monsanto which produce the genetically modified soybean seeds. Perhaps companies like Cargill Foods or SoyLife which produce countless soy-based foods. Or soybean councils in several states which represent farmers who grow this new, emerging bumper crop. And, of course, all of the companies which are constructing factories all over the world to do the processing which is necessary to make soybeans edible.


Каталог: Chuong%20Vit
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