I found this study on the AST website.. it sites MANY references to medical studies about soy protein.. telling ALL about the good and the bad.. it's a long read but for someone taking soy protein right now it might be helpful to read this..
Is soy a good protein for bodybuilders? The facts on soy protein’s benefits and health risks: The soy truth and nothing but the truth!
by Paul Cribb, B.H.Sci HMS
AST Director of Research
Research has only begun to reveal the impact that different dietary proteins have on human health. Soy protein has been the subject of extensive research however, a ton of conflicting information has been put forward by the scientific community regarding soy protein’s potential benefits and risks to health. While some studies extol the virtues of incorporating soy into the diet, an equal amount of research warns us of soy’s potential for undesirable side-effects. So who and what can consumers really believe? Just recently, I was asked by the United States Dairy Export Council to review all the research on soy protein. I dug deep into the science and unearthed some very interesting facts, many of them are important to bodybuilders. I also obtained a valuable insight behind the research. I decided to share this information so that the health-conscious person can make an informed decision on the best types of proteins they should consume in their diet. I must warn you that some of this information is going to surprise you and possibly shock some of you.
The nutritional profile of soy
Soy protein isolate (SPI) is produced from soy beans via water extraction, precipitation, washing and drying procedures. SPI is approx 90% protein and is very low in carbohydrate and fat and contains no cholesterol. Whereas dairy proteins are readily accepted as complete proteins (they contain all essential amino acids), soy protein is deficient in methionine and contains a low concentration of another essential amino acid, lysine. However, with fortification and the concentration of amino acids during its manufacture, SPI is considered to be a complete protein that contains adequate amounts of all essential amino acids (the building blocks of all proteins within the body).[1] Aside from its high protein content, SPI also contains naturally occurring phytochemicals (isoflavones) such as daidzein and genistein. These are the main isoflavones of soy and they have been widely researched; their concentration can be specifically increased or decreased during the manufacture of SPI.[2] Despite the claims made by marketers of soy products, it is still unclear whether the purported health benefits from SPI are due exclusively these isoflavones. Health benefits have been documented with soy proteins that are rich in, or totally devoid of these phytochemicals.[3]
The facts behind the research on soy’s health benefits
Soy protein’s ability to improve blood cholesterol profiles and reduce the risk of cardiovascular disease has become widely accepted by the health care community. This is due largely to a health claim approved by the Food and Drug Administration (FDA) back in 1999. However, this approval is still considered to be controversial.[4] Most of the evidence to substantiate this claim was obtained from the results of an inaccurate meta-analysis study published in 1995.[5] A more recent analysis of the all the relevant research on SPI supplementation and its effect on blood cholesterol concluded that no dose-response relationship could be found. In other words, the consumption of soy protein could not be attributed to improved blood cholesterol profiles.[6] Additionally, most of the recent studies that have shown benefits from SPI on blood cholesterol profiles have attributed the benefits to a reduction in animal fat and/or an increased intake of vegetables in the diet rather than any unique biological action from soy.[7,8,9,10]
Coronary heart disease remains the leading cause of death of adults in the United States. Soy isoflavone supplements and soy-fortified foods are often marketed to older adults to promote better cardiovascular health. However, no studies have been able to show that supplementation with isoflavones (in pills, capsules and fortified foods; 80-150mgs/day for up to six months) provides any protection against cardiovascular disease.[11,12,13,14,15] These results are particularly relevant as 80mgs of phytoestrogens is a reasonable level that can be obtained in the diet.[15]
One serious adverse effect on arterial health (endothelial tissues) has been reported.[66] In this study of 213 humans (108 men and 105 women, 50–75 years old), SPI supplementation (40gms/day for 12 weeks) did not improve vascular function. Aside from a 15% increase in blood fat levels, a decline in endothelial function was documented in the men that consumed SPI.[66] Endothelial dysfunction is an early marker of vascular disease. The results of this study showed that SPI treatment created a decline in brachial artery dilation (a clear indication of poor endothelial function) in men and had no beneficial effect on the in women.
Based on the results of cross-sectional studies on Asian females, soy products are often marketed to women in the United States to improve bone health. However, it must be noted that at least half of these studies show that soy foods provide no beneficial effect on bone health. [16-19] The most favorable data on soy’s effect on bone health has come from cell-culture and animal studies but in terms of research on humans, only two of five clinical trials have shown positive results.[21-25] Despite the weight of scientific evidence that suggests soy does not provide a clear beneficial effect on bone and cardiovascular health (as well as some research that has shown one bad side effect), the FDA has not with drawn its approved health claim about soy.
Soy protein’s immune and anti-cancer effects
The ability to avoid many forms of illness and disease depends largely upon a strong immune system. Research now shows that the type of protein in the diet can influence the efficacy of the immune response. Some studies with animals show that soy is capable of improving some aspects immune function. However, studies that have compared SPI to whey protein isolate show that supplementation with whey protein provided a superior immune-enhancing effect in every key facet of immune function.
An integral role of the immune system is to reduce oxidative stress. By virtue of its isoflavone content, soy protein shows the potential to reduce excessive free radical production that causes oxidative stress,[31] but research is yet to confirm this benefit in humans. Marketers of soy protein products often cite two studies that reported significantly greater reduction in oxidative stress from SPI in comparison to whey protein supplementation.[32,33] However, when quoting these studies, the marketers of soy products neglect to inform consumers that the methodologies employed in these investigations were very limited. In one study, the treatments were not disguised to prevent bias (not double-blinded) and a decrease in oxidative stress was reported from only one blood collection after the exercise/supplementation treatment.[33] Usually, these kinds of studies obtain multiple (hourly) blood collections for up to 24 hours as well as daily samples for a further 21 days! The other study reported that SPI reduced plasma lipid peroxides (a marker of oxidative stress).[32] Scientists in this area of research recommend that correlations from at least two or more biological assays should be apparent before any discussion regarding oxidative stress can be made.[34]
The glutathione (GSH) antioxidant system controls many of the key processes of immune function. Optimization of the immune system is attributed directly to a greater production of GSH in the immune cells, particularly the lymphocytes.[34] Maintaining adequate GSH stores within cells is also shown to correlate with better improvements in body composition during exercise. [35] While supplementation with high quality whey proteins (20-60gms/day) are shown to improve GSH status under a variety of conditions (from HIV to intense athletic training), soy protein is shown to have no beneficial effect on GSH production. [26,28,30,37] Maintaining GSH helps build muscle and strip away body fat as well as strengthen the immune system. Therefore, bodybuilders and other athletes need to be aware that only high quality whey proteins such as VP2 Whey Isolate are the only protein sources capable of improving GSH status.
Of all environmental factors known to influence the risk of cancer, diet appears to be one of the most significant. Evidence from cell-culture and animal studies suggest that soy may protect against some forms of cancer. However, in studies that have compared the effects of whey to soy protein, whey protein’s ability to inhibit/reduce carcinogenesis is shown to be twice as effective. [37-40]
Soy products are often marketed to women to provide protection against estrogen-dependant cancers such as breast cancer. However, only one intervention study has managed to provide evidence that soy protein supplementation affects estrogen metabolism to provide a cancer-preventative effect.[41] All the other studies that have examined this topic report that soy protein supplementation (40 to 80gms/day) exert no effect on estrogen metabolism in young and older women.[41-45] Some studies with animals suggest that a diet high in soy isoflavones may protect men against development of prostate cancer.[46] However, only one randomized, double-blinded clinical trial has been completed and the results showed that 12 months of SPI supplementation offered no protection against a gradual increase in circulating PSA levels (an intermediate marker of tumor growth) in older men.[47]
Effects on metabolism, muscle gains and fat loss
Soy proteins such as SPI contain a much lower concentration of the essential amino acids than dairy proteins (such as those found in VP2 Whey Isolate and Ny-Tro PRO-40). The ratio of amino acids within SPI is also very different to dairy proteins. These two important aspects underline the different impact that soy and dairy proteins have on the metabolism and the ability to build muscle. Unlike dairy proteins, SPI does not exert an anabolic effect on muscle. A high proportion of SPI’s amino acids undergo deamination (degradation) by the liver during digestion.[47,48] Therefore, the amino acid pattern that enters circulation is ineffective at stimulating protein synthesis and depositing nitrogen in muscle and other tissue.[47,48,50]. In comparison, the consumption of whey protein results in stimulation of protein synthesis and high net protein gains within muscle after each meal.
Bodybuilders know that a high protein diet is essential for muscle gains and effective fat loss. One recent study has shown that SPI supplementation may actually retard muscle gains when consumed as part of a high protein diet.[51] In this study, supplementation with SPI (38gms/day for an 80kg person) during a high protein diet resulted in a loss of dietary nitrogen (protein) compared to supplementation with dairy proteins.[51] The results showed that SPI supplementation increased the amount of protein in the diet that is converted to urea (an unusable by product of protein metabolism excreted by the body). Therefore, SPI supplementation appears not only to be less effective at stimulating the mechanisms that promote recovery and muscle gains; the consumption of SPI during a high protein diet actually promotes the loss of protein within the body. The exact opposite of what bodybuilders want to achieve. When it comes to nutritional choices for building muscle, misguided doctors and nutritionists will tell you that protein is protein. However, the results of this study clearly demonstrate that SPI supplementation increases protein losses within the body and this effect would definitely not help a person gain muscle during weight training exercise.
Bodybuilders know that intense resistance (weight) training is the only activity that promotes a simultaneous increase in lean tissue and a decrease in body fat. Supplementation with dairy proteins after a weight training workout is shown to provide higher net gains in muscle protein compared to soy.[52] In the long term, the benefits of incorporating VP2 whey Isolate into the diet during resistance training are clear. Studies have shown that VP2 provides faster recovery, a 2-5 fold better gain in lean body mass and muscle strength as well as effective fat loss compared to other supplements. No well-designed studies have been able to show that SPI may promote muscle or strength gains or fat loss during weight training exercise.
Some proteins provide an appetite-suppressing effect that makes dieting for fat loss much easier.[53] High quality whey proteins are also shown to stimulate an appetite-suppressing via a higher secretion of two gastrointestinal hormones (cholecystokinin and glucagon-like peptide-1) that control appetite. A whey protein shake consumed 30 minutes before a meal provides a greater feeling of satiety (fullness) from the consumption of less food. In comparison, soy proteins do not provide these benefits. [54]
The concern for adverse health effects from soy protein consumption
The general public (as well as a lot of scientists), are confused about the real facts on the safety concerns of soy protein. The anxiety about soy’s potential for adverse effects pertain exclusively to its isoflavone concentration and the impact dietary isoflavones may have on sex steroid metabolism. The potential estrogen-mimicking effects of soy isoflavones has raised the concern that these phytoestrogens may be a double edged sword; provide benefits to some populations while creating risks in others. However, after careful perusal of all the literature on this topic, I’ve found at least one paradox.
Some scientists caution that a high consumption of soy isoflavones by humans may alter sex steroid metabolism and increase the potential for developmental toxicity and estrogen-related carcinogenesis.[55] To fuel these concerns, data from some animal studies have shown that high levels of isoflavones cause various reproductive problems. However, important consideration to specie differences in the metabolism of isoflavones has been largely ignored in the application to humans.[3] In contrast, clinical intervention trials in both men and women reveal virtually no impact (beneficial or adverse) on sex hormone metabolism from soy protein consumption.[42,43,44,45,56] A modest effect on estrogen metabolism has been documented only in older women, and this effect is most likely to be beneficial.[41]
Concern has been raised that a high intake of soy isoflavones may cause thyroid metabolism abnormalities.[55] This is based on studies that show genistein is capable of inhibiting thyroid peroxidase, a key enzyme in the production of thyroid hormones.[57,58] Genistein (a major soy isoflavone) injected into mice at 8 mg/kg per day caused significant thymic atrophy.[59] These results are relevant as the serum genistein levels obtained from the injections are comparable to those reported in soy-fed human infants.[59] Thyroid plays a key role in human development. Infants that are fed soy formula are the largest consumers of soy in the North America.[60] However, it has been established that the biological effects of naturally occurring isoflavones contained in SPI differ substantially to the effects of purified isoflavones.[61] Additionally, the potential adverse effects of purified isoflavones have not been replicated with high dose SPI or soy infant formula.[61] Extensive reviews on the safety of soy-based infant formulations have been unable to find data that suggests soy protein consumption may affect human growth, development or reproduction.[60]
The biggest misnomer in the literature has been the liberal classification of soy isoflavones as “estrogens”. Soy isoflavones are non-steroidal in chemical structure but due to the presence of the phenolic rings (particularly the 4-hdroxyl) they have the ability to bind to parts of the estrogen receptor (ER) complex. However, when soy’s isoflavones bind to the ER complex they provide distinctly different transcriptional actions to estrogen.[62] Insightful x-ray crystallographic studies have shown that the conformational binding of soy isoflavones to the ER complex is very different to estrogen and very similar to selective estrogen receptor modulators (SEMS) such as raloxifene.[63,64] Soy isoflavones bind to the ER and act more like SEMS and therefore, are more likely to provide protection against estrogen related cancers [3,62] While clinical trials are warranted to clarify this, it is difficult to find clear evidence that refutes this hypothesis that was made over 20 years ago.[65]
There are some isolated findings that warrant further explanations such as arterial dilation in men[66] and depression of some markers of immune function.[29] However, when viewed in its entirety, the vast majority of the literature regarding the potential for genotoxicity, carcinogenicity, reproductive and developmental toxicity, supports the safety of soy protein consumption in the typical U.S. diet.[60,61,67,68,69] It is interesting to note that some of the scientists who support the safety of soy consumption also caution that as long as nutraceutical companies persist in flooding the market with products that contain high levels of soy isoflavones, far in excess of the amounts shown to provide beneficial effects, there exists the potential for long term negative consequences.[70]
The bottom line from all this information is that unfortunately, consumers can’t believe everything they read about many “health foods”. Despite an FDA approved health claim, the scientific literature on soy protein’s beneficial effects on bone and cardiovascular health is at best, contradictory. Although soy protein demonstrates immune-enhancing, anti-cancer properties, studies that have compared soy to whey proteins directly, show that whey proteins are twice as effective at protecting against cancer and enhancing immune function. In contradiction to the health scares, human trials reveal a benign effect from soy protein consumption on estrogen metabolism. The fact is it’s difficult to find evidence that soy protein consumption has an adverse effect on sex steroid metabolism in men or women, young or old. From a bodybuilding perspective, protein metabolism research demonstrates that soy exerts very little effect on the mechanisms that build muscle tissue, and some data suggests that SPI supplementation promotes the loss of protein within the body. This effect would definitely impede a person’s ability to recover and build muscle during training. These are the facts on soy protein; the soy truth and nothing but the truth!
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