Soy: Sunshine and Shadows
Stephen Holt, MD, LLD(Hon.) ChB., PhD, ND, FRCP (C) MRCP ( UK ), FACP, FACG, FACN, FACAM, OSJ
Throughout my writings, I applaud repeatedly the versatile and potent health benefits of the soybean. In recent times, however, there has been considerable argument about the proposed health benefits of soy. Predictably, the most vociferous criticisms of soy in the diet have emanated from the meat and dairy lobby and their representatives in the media and scientific community. Soy is probably the prime example of a �medicalized� food and although its health benefits are great, it is not to be used alone, with the exclusion of a balanced diet.
About ten years ago, there were several hundred medical citations per year on basic and clinical scientific research involving the biological effects of soy. In the calendar year 1999, there were several thousand such articles. Major universities, research institutions and the Federal Government have shown a willingness to fund research projects that examine the health benefits of soy. Soy contains several nutrient and phytochemical fractions that may prevent and perhaps treat a variety of chronic diseases such as atherosclerosis, hyperlipidemia, osteoporosis; and it may play a role in breast or prostate cancer prevention and perhaps treatment. The value of soy protein as a staple portion of the diet is being recognized in weight control and as nutritional support for athletic pursuits, with a special role in the maintenance of lean body mass.
Too good to be true!
Suspicion should arise in anyone’s account of a specific food type that claims this massive array of benefits. On the downside, unprocessed soy bean is unfriendly food and it does not appeal generally to the Western palate. The flatogenic potential (intestinal gas forming) and strong aftertaste of unprocessed soy is known to many. However, modern food processing and ancestral fermentation techniques renders soy quite palatable. These processes alter the flavor and mouth feel of soy so that it can satisfy Western taste preferences.
At first sight, the circumstances of �soy for health� seem ideal and thoughts about soyfood could consistently conjure up the idea of a panacea health benefits. However, a lot of soy food consumed in Western society is highly processed and as a consequence it is subject to the elimination of certain health giving fractions of soy. Some soy foods have uncertain advantages for health. A classic example of this circumstance is the widespread inclusion of hydrogenated soy bean oil in junk food. In fact, current estimates imply that soy bean oil in this format may be one of the principal sources of calories in the North American diet. We need little instruction concerning the demonstrated negative health consequences of hydrogenated oils, especially if they contain significant amounts of trans fatty acids. Trans fatty acids are damaged kinds of fat that have been associated with heart disease.
The tragedy is that unprocessed, fresh soy bean oil is one of the best sources of health giving omega-6 fatty acids and it is distinguished by being one principal plant source of precursors of omega-3 fatty acids, akin to flax seed oil. The adulteration of soy bean oil to fit our learned �fat taste preference� for junk food is one classic example of how commercial interests may relegate the importance of healthy nutrition. I must indicate my strong protagonist and unwavering opinion that soy has major health benefits, but modern humankind may not be using technology in ways that capitalize on the health benefits of soy.
Negatives and positives
Against this background, it seems relevant to address issues raised by several groups who focus on the negative perspectives of soy. The issue is that correctly prepared and unadulterated soy has few limitations as a primary source of health giving constituents in the diet. There is, however, a strong lobby to undermine the demonstrated health benefits of soy and this lobby is driven by huge commercial interests including, meat and dairy purveyors who are backed by the massive economic power of the fast food and junk food industries. The lay press tells us that if we placed each hamburger that had been consumed from fast food chains in a side by side lineup, we would have a pathway to the moon and back! I do not think that the occasional hamburger is unhealthy, but our intakes of hamburgers and other �goodies�, such as ice cream and chocolate, are staggering.
Opinions about any negative health consequences of soy food often result from misinterpretations of existing literature. There are some highly conservative, �educational� foundations that cling to the notion that excessive saturated fat intake is consistent with general health. In contrast, several �weight loss gurus� propose liberal saturated fat intake as an efficient way to lose weight. On balance, the evidence for excessive intake of unhealthy types of fat in the promotion of obesity, cardiovascular disease and cancer is overwhelming. In fact, obesity is the commonest nutritional problem in Western society and it goes hand in hand with heart disease which is the commonest cause of death.
This cautionary message should not be diluted by short term weight loss benefits of high fat and protein intake together with the focused criticism of vegetable protein diets by protagonists of the obsolete �meat and fried potato� movement. The induction of ketosis by severe carbohydrate restriction and increased fat intake induces weight loss as a consequence of early fluid loss, the induction of anorexia and the elimination of a substantial source of calories in the diet from carbohydrates. Whilst this approach to weight loss may cause short term success, it may be associated with unknown cardiovascular risks and other health problems, especially if this dietary approach is applied in a sustained manner. No credible evidence exists that high fat and high protein intake is healthy in the long term, even though it may have some questionable value as a �short term� adjunct to weight loss.
Soy and the heart-revisited
In the past year, not one journal in the professional, consumer or trade segment of the dietary supplement industry has failed to carry more than one article on the upside or downside of soy for health. This enthusiasm, or focused antagonism for soy has been growing over the past decade. After much lobbying, the Food and Drug Administration provided their support for the claim that soy protein in the correct amount and format is capable of lowering blood cholesterol and preventing heart disease.
Whilst this cardiovascular health benefit for soy is real, a certain amount of soy fractions in the correct format need to be consumed in a monotonous manner, in order to achieve this desired health benefit. Soy sales have grown exponentially in the health food industry in the past six months. This casts a great ray of sunshine on soy, but �lurking in the shadows� is the presence of irresponsible health claims about certain soy supplements. Some dietary supplements made from soy are presented in the wrong format to carry the claim of blood lipid lowering, or other claims about the useful biological effects of soy.
According to the FDA ruling, products that contain at least 25 grams of soy protein per serving and that meet the FDA’s criteria for a �low-fat, low-saturated fat and low-cholesterol food� may feature one of two claim wordings on the label, one of which reads: �25 grams of soy protein a day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease. A serving of (name of food) supplies ______ grams of soy protein�. The other claim label food manufacturers may use reads: �Diets low in saturated fat and cholesterol that include 25 grams of soy protein a day may reduce the risk of heart disease. One serving of (name food) provides ________ grams of soy protein�. Some commercial corporations have favored an abbreviation version of the claim that would be more consumer friendly, with qualification of 6.25 grams of soy qualifying for the claim.
The evidence that soy protein in a dose of at least 25 grams per day can be expected to lower blood cholesterol is quite convincing. In fact, this health advantage of soy has been known for approximately 50 years. One impediment to the popularization of soy protein for cholesterol lowering in medical practice has been an incomplete understanding about how soy lowers blood cholesterol. This question has not been completely answered in scientific studies and the current allowable claim by the FDA may represent a �deck of cards� with one or two cards short!
The amino acid profile of soy protein is known to affect insulin glucagon ratios in the blood and induce changes in the liver that may affect cholesterol synthesis and transport. Soy seems to alter thyroid status by producing modest elevations of serum thyroxine levels in animals and humans. Whole soy food contains soluble and insoluble soy fibers that can assist in cholesterol lowering by interfering with fat and cholesterol absorption. These mechanisms of action of soy on altering blood lipid profiles are still being clarified by biochemists.
One important fraction of soy that has measurable cardiovascular benefits are the isoflavones (principally genistein and daidzein). These isoflavones are powerful antioxidants and they may be a key fraction of soy that assist in the promotion of cardiovascular health, independent of an ability to contribute to the lowering of blood cholesterol. It has been accepted that soy protein alone is responsible for lowering blood cholesterol, but data are conflicting about the ability of isoflavones alone to contribute to the known cardiovascular benefits of soy.
The data on cholesterol lowering
A closer look at the data on the ability of soy protein to lower cholesterol that isoflavones are invariably present in soy protein isolates. These protein isolates have been studied in cholesterol lowering clinical trials and shown to be effective in a consistent manner. The FDA approved claim for soy and cholesterol focuses on the effects of soy protein alone. I believe that the value of soy isoflavones in promoting cardiovascular health should have been recognized by the FDA prior to the assent of the cholesterol lowering claim for soy, but arguments prevail.
There is a further issue of deficiency in the allowable claim for soy and cholesterol lowering. The amount of soy protein recommended for cholesterol lowering is 25 gm. This is at the lower limit of the amount of soy protein shown to be effective at lowering cholesterol in clinical trials. In fact, a dose of approximately 25 grams per day is probably optimal for lowering blood cholesterol in children but more may be required to achieve the ideal therapeutic outcome in adults.
I am concerned that consumers of soy may take 25 grams of soy protein per day and not realize that they may need to increase the dose if they do not achieve reductions in blood cholesterol. Therefore, the current claim approved by the FDA could contribute to premature conclusions about therapeutic failure of soy protein to lower cholesterol. This could in turn result in the premature prescription of a cholesterol lowering drug. Why is this situation so important?
Over-prescription of cholesterol lowering drugs?
Conventional medicine has been criticized for excessive and premature prescription of cholesterol lowering drugs without appropriate application of the first line options of dietary adjustment, exercise and adequate lifestyle changes. Lowering cholesterol is not a medical emergency. It seems that dietary adjustments with the application of natural agents that may lower blood cholesterol (e.g. soy protein, fish oil, garlic, yeast treated rice etc.) could obviate the need for the prescription of perhaps as much as 60 % of all lipid lowering drugs. This is a best guess.
Furthermore, these natural options are compatible with the simultaneous use of lipid lowering drugs and use of these cholesterol lowering, dietary supplements may permit the reduction of dosage requirements of blood lipid, lowering, drugs. Since adverse effects, such as altered liver function and muscle damage, may be somewhat dose related for �statin�-type lipid lowering drugs, there may be clear advantages for at least the adjunctive use of natural agents (such as soy protein) for the lowering of blood cholesterol. I reiterate that one must be vigilant about soy supplements carrying cholesterol lowering claims that do not contain the correct amount or fraction of soy to achieve this desired health effect.
Pushing the envelope
A good example of �pushing the envelope� on soy health claims has been the widespread popularity of chocolate bars containing soy that carry questionable, and perhaps even misleading health claims. It seems that certain segments of the health food industry want to adulterate soy whilst masquerading behind its defined health benefits – after compromising or destroying these benefits by �modern� manufacturing techniques. This circumstance exemplifies one of the principal difficulties of converting soybean foods or fractions to fit the Western palate, whilst still retaining its health benefits.
Examples of this �masquerade� are all too frequent in certain soy supplements. For example, chocolate bars containing soy protein in insufficient amounts to lower cholesterol or containing insufficient amounts of isoflavones to have the benefits of these phytochemicals should be perceived with the utmost skepticism, especially when health claims are made. Some of these �health� bars are spiked with hydrogenated oil or oils containing unwanted amounts of saturated fats, such as palm oil. They do not taste as good as popular, chocolate candy bars and have few definable, health advantages over this types of confection.
There is a minor price to pay if one wishes to derive measurable health benefits from soy protein. Soy protein isolates can be taken as bland tasting powder in a minimum dose of 25 grams per day. Most soy protein isolates contain an average total isoflavone content of about 2 mg/g. These powders can be used in cooking or they can be made into a �smoothie drink� that has an exceptionally good mouth feel; and it can be flavored as required with fruit juice. Some of these powders carry the added advantage of the inclusion of fractions of fermented soy.
Fermented or non-fermented soy?
A prevailing opinion exists among some nutritionists that the health benefits of soy are most likely to be delivered when soy is given in a fermented format. Soy has been a dietary staple in Eastern Asia for thousands of years and traditional, soy-based diets are composed often of fermented soy bean products including miso, natto or ancestrally fermented tofu. Much of the evidence for the health benefit of soy in the diet is derived from population studies that compare Eastern Asians on soy rich diets with Westerners taking diets that contain more animal protein and refined carbohydrates. These epidemiological studies show that the occurrence of breast or prostate cancer, heart disease and adverse symptoms associated with the menopause is less in populations consuming soy. In many circumstances the type of soy consumed in these populations is of the fermented variety.
This line of reasoning to support only the use of fermented soy for health is not entirely convincing because fractions of soy using modern food processing techniques, such as isolates of soy protein, have been shown in modern, well controlled, scientific studies to have measurable health benefits. The real advantage of fermentation is the partial digestion of protein and carbohydrate components of this legume. Enzyme inhibitors within soy are often denatured, removed or neutralized by fermentation and unabsorbable carbohydrate fractions of soy that cause digestive upset, such as abdominal gas and bloating, are substantially eliminated.
Recent research on the absorption and biodisposition of soy isoflavones shows that these compounds have a greater bioavailability (enhanced absorption) when presented to the gut for absorption in deconjugated form. The conjugated isoflavones genistin, daidzin and glycetin are converted variably to their unconjugated forms (genistein, daidzein and glycetein) by the breaking of a chemical bond during fermentation. Therefore, fermented soy can be expected to present freely bioavailable isoflavones that can be efficiently utilized. Pharmacokinetic studies of soy isoflavones support the notion that unconjugated isoflavones have enhanced systemic bioavailability (better absorption and availability to the body).
The story of the change of composition of soy fractions during fermentation is not simple. The various fractions of soy and their chemical make up may vary considerably due to many factors including the nature of starting substrates, agents (yeasts or fungi) used for fermentation and physiochemical factors used in various fermentation processes.
Although isoflavones are often present in the soybean seed as conjugated compounds, a variable amount of these phenolic compounds have a substitutions in their conjugated structure with a malonyl group. Furthermore, the chemical characteristics of the isoflavones can vary by their location within the seed. For example, the hypocotyl segment of the bean may have greater amounts of malonyl substituted conjugated isoflavones than other sites within the bean.
Examples of the variability in soyfoods as a consequence of biotransformation by fermentation or other processes include: a low concentration of malonyl substitution in roasted beans, a reduction of isoflavone levels in tofu because of aqueous processing, higher levels of isoflavones in aglycone (deconjugated format) in tempeh than in soynatto etc. The purpose of this discussion of variability of soy ingredients induced by fermentation and other food processing conditions is to reinforce some of the advantages of soy supplements which contain predictable amounts of certain fractions of soy. In addition, there is a relative absence of soy foods that are standardized for their health giving constituents. Soy is an ideal substrate for the development of dietary supplements or functional foods, but the health properties of �functional food� are only guaranteed by standardization of ingredients. This type of standardization (or engineering) of soyfood is not an easy task.
In summary, fermentation has some clear advantages in permitting the conversion of soy in its unfriendly crude format into a friendlier format. In addition, certain health giving fractions of soy may be more readily utilized after fermentation; most notably the isoflavones in soy that have been associated with potent and versatile health benefits.
The enigma of soy for health
The widespread interest in the health benefits of the soybean has political, economic and social implications for Western society. After many years of questioning the �meat and potatoes� diet of the West, the possibility of a major dietary switch from animal or dairy protein to vegetable protein, as found in soy, is now a real prospect. Diet plays a major role in disease prevention and causation. The negative consequences of a high meat or dairy protein intake couple with saturated fat and refined carbohydrates is eclipsed by the apparent, protean benefits of soy for health. In my view, these health benefits of soy require definition in the correct context.
Renaissance of Soy
The renaissance of interest in soy has occurred with predictable contentions and differences of opinion. Despite strong opinions about the health benefits of soy, I have reacted against certain panacea claims for the health benefits of soy, especially when soy is modified by certain types of food processing. In fact, the most commonly consumed fraction of soy is hydrogenated soybean oil. This oil is prime component of �junk food�. The use of soy as a �meat substitute� may not be the most ideal or healthy presentation of soy. Furthermore, it carries a connotation that soy is an inferior type of protein. Protein digestibility scores for soy show that soy is indeed an ideal protein.
The isoflavone debate
The most debated components of soy for health are the isoflavones, to which many health benefits have been attributed. The soy isoflavones, (genistein and daidzein) appear to exert cancer preventive benefits, especially if they are taken in early life. However, a small group of scientists have hypothesized that soy isoflavones may increase the risk of cancer in selected circumstances.
Population studies and animal experiments support the anticancer effects of soy isoflavones for breast and prostate cancer primarily, with more tenuous evidence that they may prevent lung, stomach and bowel cancer. The notion that isoflavones may promote the growth of cancer humans is merely an inference from the observations of the estrogenic actions of isoflavones in cancer tissue in vitro and in animal experiments; where estrogen dependent neoplasia has been studied. Much confusion prevails among lay persons and the scientific community about the cancer preventing (or promoting) properties of soy isoflavones.
Dissecting the actions of isoflavones
The confusion about the role of isoflavones in cancer inhibition or promotion is attributable to our current lack of knowledge about the biological actions of these compounds. One simplistic and misleading point of view has been to categorize isoflavones as �phytoestrogens� with unqualified, estrogenic effects. Isoflavones have an affinity for estrogen receptors but they tend to exert lower �levels� of estrogenic stimuli to cells than do endogenous estrogens, such as 17-beta-estradiol. In crude terms, this means that isoflavones could be a kind of �balancing act� for the effects of endogenous estrogen on tissues in the body. Extensions of this simple, conceptual model imply that isoflavones may become a kind of �biochemical adaptogen� for estrogen activity in the body.
Recent work suggests that isoflavones, like other phytoestrogens, could exert effects on estrogen status by altering the metabolism of estrogenic compounds in the body. Isoflavones do not have a consistent proestrogenic action. In states of estrogen dominance, their occupancy of estrogen receptors could make their overall effect antiestrogenic (blocking the action of more potent endogenous estrogens). Clearly, these circumstances of a potential role for soy isoflavones as a modifier of biological responses are not simple and they require further scientific exploration.
Conflicting data on isoflavones
An impressive and increasing body of data on the effects of isoflavones on cancer tissue has emerged in the past two years. Data in animal experiments that observe the growth of transplanted tumors have produced apparently conflicting data. Estrogen dependent tumors examined in vitro or in tumor transplants (e.g. xenografts) may show does dependent differences in response to isoflavones administration. The recent demonstrations of the experimental promotion of the growth of specific estrogen sensitive tumor types with isoflavones has led to a lot of �fence sitting� on the issue of isoflavones in cancer prevention. The key, however, to understanding the health benefits of isoflavones is to understand their potent and versatile biological effects that are independent of any effects that they have �estrogenic drive� in the body.
Versatility of isoflavones
Isoflavones many exert anticancer benefits by their function as potent antioxidants and free radical scavengers. Experiments in animals and limited human observations show that isoflavones exert an antiangiogenic effect. Angiogenesis is an important step in the pathogenesis of cancer. In addition, genistein can interfere with key enzymes that are important in cell proliferation and tumor growth. Isoflavones inhibit tyrosine kinase and DNA topoisomerase. Topoisomerase is involved in expression of cellular apoptosis.
Thus, the ingenious isoflavones have potential anticancer effects that act independent of any estrogenic or antiestrogenic activity. Despite these uncertainties about the actions of isoflavones, the sale of dietary supplements containing isoflavones rose by a factor of approximately 250% in a 12 month period, ending October 1999. This circumstance has caused concern in some ranks of food science.
Are isoflavones safe?
Soy isoflavones appear to be safe when used in doses where a precedent for safety exists. It is unlikely that an individual would consume more than a total daily intake of 150 mg of isoflavones, even in the most heavily enriched soy diet, such as may be encountered in a few oriental communities. Researchers have pointed to the strength of epidemiological data that supports the role of soy in diminishing the occurrence of cardiovascular disease, breast or prostate cancer and menopausal symptoms in Asian versus Western populations. However, there are clear problems when one draws conclusions from population studies alone, because the operation of several variables in such studies can confound suppositions or conclusions. However, carefully applied statistical techniques that are used to factor out other influences on health in population studies of the health benefits of soy tend to show an independent beneficial health effect of soy in the diet.
There is a general tendency for people to believe that soy consumption is very high in Eastern Asian communities. In fact, traditional soy based diets have peaked in their use and diets in the Orient are becoming increasingly �westernized�, especially in urban locations. Average levels of consumption of soy isoflavones in urban areas of Japan and Korea may be as little as 10 mg per day and falling! This phenomenon has shown us the �other side of the coin�. As Eastern diets convert more to Western cuisine, the typical Western disease profile shows a tendency to emerge in the Eastern culture.
Soy is not the whole story
Of course, soy may not be the whole story. The lower incidence of cardiovascular disease or prostate and breast cancer in Japan has been linked not only to soy but also to an enhanced intake of dietary fiber, fish products (omega-3 fatty acids) and vegetables. Whilst I acknowledge soy is not the whole story in accounts for the apparent improvements in certain disease profiles, I believe it to be of great importance.
There is a �trap of convenient thinking� when one looks at cardiovascular and cancer problems in Eastern Asia . The protagonists of soy for health seem to forget the alarmingly high occurrence of stroke and stomach or esophageal cancer in the Orient, compared with Europe and the US . One dietary factor causing this problem seems to be salt intake.
Scary reporting � The soy panic
Any issue in science that is reduced to lay reporting is subject to innocent distortion. The �story of soy� is the victim of this circumstance. On January 26 th , 2000 in the midst of excitement about the benefits of soy for health, the New York Times published an article entitled �Doubts Cloud Rosy News on Soy�. This account of soy and health focused on isoflavones, with the bold unsubstantiated statement �and there may be an increased risk of cancer associated with consuming the components soy called isoflavones in supplement form, particularly for post-menopausal women; and for these women, there may also be hazards in adding soyfoods to their diets�. This article sent many women running to their healthcare provider in a state of �soy panic�.
Although the article impeached the safety of soy by referring to interviews with scientists, not one of the interviewed scientists said outright that soy causes cancer. These scientists cautioned about the unknown effects of higher doses of isoflavones in supplement format. Some of the scientists interviewed by the New York times are on record as extolling the anticancer effects of soy and even presenting data on isoflavones as a viable alternative to estrogen replacement therapy in females of menopausal age. Clearly, unresolved contention exists and predictable confusion prevails.
Addressing this issue
Any estrogen (or pseudoestrogen) will be expected to exert an estrogenic effect, so why the need for panic? Recent data reassure us that several decades of use of estrogenic compounds in oral contraceptives have not produced major problems. Furthermore, potent estrogens are given by prescription for menopause, despite concerns about uterine and possible breast cancer promotion.
Soy isoflavones present the body with a much weaker estrogenic stimulus than these prescription drugs (contraceptives or hormone replacement therapy, HRT) and not one scientific study has ever shown that soy based diets promote cancer in humans. Furthermore, none of the other estrogens in our environment (xeno, pseudo or prescription) have the general array of benefits associated with soy isoflavones. Amidst the contention, medicine has embraced the use of tamoxifen, a potent carcinogen, to prevent breast cancer but it appears to have been forgotten that isoflavones could block the action of other undesirable or toxic endogenous or exogenous estrogens. �Naturally�, medicine’s bias towards the drug prescription has led to new research protocols to examine selective estrogen receptor modulating drugs in breast cancer prevention, rather than consider isoflavones.
Megadoses of isoflavones are not advised, except as part of an approved, experimental, clinical protocol. The problem is that a safe dose of isoflavones in supplement format defies accurate definition. Looking at isoflavone concentrations in soy enriched diets gives us a rough idea of the precedence of safety of isoflavones in humans. A guess for a safe dosage of isoflavones is about 80 mg/day of total isoflavones (in natural, conjugated format) but no more than 120 mg-day. These numbers have to be revised downwards in circumstances where freely bioavailable (aglycone, unconjugated) isoflavones are used, such as those found in fermented soy. In this format, a guess is perhaps no more than 45-60 mg of total aglycone, isoflavones per day. These recommendations have to be assessed with the knowledge that there is substantial inter-individual variation in the biodisposition, pharmacokinetic and pharmacodynamic effects of isoflavones.
I admit that these �recommended amounts� of isoflavones are estimates or guesses, based on safety precedents from oriental diets and some �inferences� from data on the amount of daily isoflavones required to provide, some desired biological effects or nutritional support for certain body functions. One must bear in mind that the beneficial effects of isoflavones on menopausal symptom relief may require a different dose than that required for prostate health. Effects on symptom relief in menopause appear dose dependent with perhaps a requirement for dose titration. These are the uncertainties of isoflavone dosage, together with the recognition that the most important compounds of soy for lowering cholesterol are soy proteins, not isoflavones. However, I reiterate isoflavones have cardiovascular benefits that are independent of their ability to be associated with changes cholesterol synthesis (e.g. interference with oxidation of LDL and antiplatelert clumping activity).
Concerns about isoflavones safety have been blown out of proportion by certain segments of the lay press. In my opinion, there is no convincing evidence that they are unsafe, except in very high doses, where the uncertain safety of any �nutrient� or phytochemical exists. In comparison to synthetic (or animal urine derived) estrogens, soy isoflavones pose less of a risk to health in terms of their �estrogenic� drive.
The Anti-aging benefits of soy
Fractions of soybeans with health giving properties are rapidly becoming the most popular category of dietary supplements. The mechanisms whereby soy may promote longevity have been overlooked despite considerable, contemporary research on soy fractions. In a condition specific, antiaging benefits of soy have been characterized (Table 1).
Table 1: Hypothetical Mechanisms for the Role of Soy Diets in Promoting of Longevity.
Condition Effects of Soya
Heart Disease Promotes cardiovascular
Hypertension and consequences Lowers blood pressure
Cancer Cancer preventative role, Isoflavones
Renal Failure Potential renal and prostate
Morbidity in old age due to:
Heart disease Promotes cardiovascular
Skeletal disorders Certain soya foods prevent
Or treat osteoporosis
Cancer Cancer preventative and therapeutic
Failing Physiological functions General good nutritional
Soy protein isolates containing isoflavones have been found to reduce cholesterol with a therapeutic equivalence to synthetic lowering drugs in Phase IV studies. Soy isoflavones have been shown to potential treatment effects in osteoporosis, cardiovascular disorder and the suppression of menopausal symptoms. Soy products have no significant adverse effects in these formulations at recommended dosages. Dietary supplements made from soy may accelerate the importance of condition specific nutritional management for the promotion of health and longevity.
• Proceedings of the Third International Symposium on the Role of Soy in
Preventing and Treating Chronic Disease, Oct 31 � Nov 3, 1999,
Washington , D.C.
• Holt S, Soya for Health, Mary Ann Liebert Inc., Larchmont, N7, 1996.
• Holt S, The Soy Revolution, Bantam Books, Dell Publishing, NY , NY , 1999.
• Messina M, Messina V, Setchell, KDR, The Simple Soybean and Your Health, Avery Press, Garden City, NY, 1995.
• Burros M, Eating Well, Doubts Cloud Rosy News on Soy, New York Times (Living Section), Jan. 26, 2000.
First International Symposium on the Role of Soy in Preventing and Treating Chronic Disease. The Journal of Nutrition, March 1995 Supplement, Volume 125, Number 3S.
Third International Symposium on the Role of Soy in Preventing and Treating Chronic Disease. Program Proceedings Oct. 31 – Nov. 3, 1999, Omni Sheraton Hotel, Washington DC .
Holt S., The Soy Revolution, Dell Publications, Bantam Books, NY, NY, 2000 and M. Evans Inc., NY, NY, 1998.
Holt S., Soya for Health, Mary Ann Liebert Publishers Inc., Larchmont , NY , 1996.
Messina M., Messina, V., Setchell K.D.R, The Simple Soybean and your Health, Avery Publishing Group, Garden City Park, NY, 1994.
This article, Soy: Sunshine and Shadows
• Discusses the importance of soy for health.
• Address issues of concern about the safety of soy isoflavone supplements.
• Discusses allowable claims for the cardiovascular benefits of soy.
• Reviews some of the conflicting data on the anticancer effects of soy.
• Describes available formats of soy in popular supplements and �health foods�.
• Proposes soy as valuable in antiaging medicine.
• 25 grams
• Genistein and daidzein
• Hydrogenated soybean oil
• Fermented types of soy
• Antiangiogenesis, Antioxidant, Enzyme inhibition
• Promotes cardiovascular health
Potential cancer prevention
Lowers blood pressure
Enhances renal function
Promotes healthy bones