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 In this section you will find updates on recently published scientific studies on soy, combined with a commentary from a member of the International Soy Advisory Board regarding the application of these findings to consumers health and well-being. Click on a title to jump straight to the study abstract and commentary, or use the browser to scroll down the page. Research Update Last updated - April 2004 Soy intake related to menopausal symptoms, serum lipids, and bone mineral density in postmenopausal Japanese women. Title: Soy intake related to menopausal symptoms, serum lipids, and bone mineral density in postmenopausal Japanese women. Abstract: OBJECTIVE: To evaluate the effects of dietary isoflavones in soy products on menopausal symptoms, lipid profiles, and bone mineral densities in postmenopausal Japanese women. METHODS: We estimated the daily intakes of isoflavones in the diets of 478 postmenopausal Japanese women who reported soy consumption. We recorded serum values of fasting total cholesterol, triglyceride, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and apolipoproteins. Bone mineral density was measured at the lumbar spine (L2-L4) by dual energy x-ray absorptiometry. Women were assigned to two groups according to years since menopause (early and late postmenopausal groups), and each group was subcategorised into four groups according to dietary isoflavone intake. Relationships between isoflavone intake, menopausal symptoms, lipid profiles, and bone mineral density were examined in each group. RESULTS: The mean estimated intake of isoflavones among 478 women was 54.3 mg/day. With stepwise regression analysis we found that weight and years since menopause were significant independent predictors of bone mineral density. Bone mineral densities adjusted to years since menopause and weight were significantly different in the highest intake compared with lowest intake category (P <.001) within the early and late postmenopausal groups. In the early postmenopausal group, significant differences were found in palpitation and backaches between the high and low intake categories but were not significant in the late postmenopausal group. CONCLUSION: High consumption of soy products is associated with increased bone mass in postmenopausal women and might be useful for preventing hypoestrogenic effects. Editors comment*: Isoflavones have been suggested as potential natural alternatives to alleviate symptoms resulting from oestrogen deficiency in the menopause. In this population-based study, the post-menopausal women with the highest intakes of isoflavones (> 65 mg per day) had a higher bone mass in the spine, compared to women with intakes less than 35 mg per day. However, there were only small or insignificant differences in menopausal symptoms and no differences in blood fat profiles according to level of isoflavone intake. These findings are interesting since on average, Japanese women already have a much higher intake of isoflavones compared to women from Western countries who usually consume < 1-5mg per day. It seems that in this population at least, a higher intake of isoflavones might provide additional benefits for bone. The authors of this study speculate that the lack of differences seen for post-menopausal symptoms and blood fats, might have something to do with the fact that even the 'lowest intake group' was probably already within the biologically active concentration where isoflavones can exert some health effects. * Sue Radd, Member of the International Soy Advisory Board Title: Effect of soy-based breakfast cereal on blood lipids and oxidised low-density lipoprotein. Abstract: Consumption of soy protein may reduce the risk of cardiovascular disease both through reduction in serum lipids and by the antioxidant properties of protein-associated soy isoflavones. However, the effect that processing required for the manufacture of breakfast cereals may have on the lipid lowering and antioxidant activities of soy has not been studied. We have therefore assessed the health benefits of soy incorporation into breakfast cereals. Twenty-five hyperlipidemic men and women took soy (providing 36 g/d soy protein and 168 mg/d isoflavones) and control breakfast cereals, each for 3 weeks in a randomised crossover study with a 2-week washout period between treatments. Fasting blood samples were obtained pretreatment and at weeks 2 and 3 of each treatment. No significant difference was seen in serum lipids between treatments at week 3 apart from a 3.8% +/- 1.5% higher apolipoprotein A-1 level on control versus soy (P = .021). However, oxidised low-density lipoprotein (LDL) was reduced on the test compared with the control both as total dienes in LDL and as the ratio of conjugated dienes to cholesterol in the LDL fraction by 9.2% +/- 4.3% (P = .042) and 8.7% +/- 4.2% (P = .050), respectively. High isoflavone intakes in soy breakfast cereals may decrease the risk of cardiovascular disease by reducing oxidised LDL, while having no significant effect on the absolute concentration of LDL cholesterol. Editor's comment*: This Canadian study is the first in the world to show that soy breakfast cereals can deliver important antioxidant benefits. The men and women who consumed a soy breakfast cereal (containing a large proportion of soy flour) daily for 3 weeks, were found to have lower levels of oxidised LDL-cholesterol. This is the 'really bad' form of cholesterol that readily deposits in blood vessel walls and is very difficult to remove, leading to hardening of the arteries. Dietary antioxidants are thought to play an important role in protecting cholesterol from being oxidised thereby reducing the risk of cardiovascular disease. Most soy foods are a good source of isoflavone antioxidants, while fruits, vegetables, nuts and wholegrains supply many other types of antioxidants to the diet. While demonstrating antioxidant benefits, the study did not show that this soy breakfast cereal reduced the actual level of cholesterol. The authors speculate that the processing used in the manufacture of breakfast cereals might have an effect on the cholesterol lowering potential of soy protein. Previous studies, where the diet was supplemented with the amount of soy protein present in this breakfast cereal, have shown cholesterol-lowering effects in men and women with high cholesterol levels. * Sue Radd, Member of the International Soy Advisory BoardTitle: NAMS Fellowship Findings: Dietary inclusion of whole soy foods results in significant reductions in clinical risk factors for osteoporosis and cardiovascular disease in normal postmenopausal women. Abstract: OBJECTIVE: To determine the effects of dietary inclusion of soy foods on clinical markers for cardiovascular disease (CVD) and osteoporosis in normal postmenopausal women. DESIGN: This was a single open-group prospective clinical intervention. Forty-two normal postmenopausal women consumed three daily servings for 12 consecutive weeks of whole soy foods containing approximately 60 mg/d of isoflavones. Blood and urine specimens were obtained at baseline and after 12 weeks of dietary intervention. RESULTS: Serum and urine levels of individual and total isoflavones increased significantly (7-19 fold, p < 0.001) from baseline. A significant increase (9.3%, p < 0.05) in the mean lag-time of low-density lipoprotein cholesterol oxidation was seen and was positively correlated with serum phytoestrogens (p < 0.05). Significant increases were found in mean levels of high-density lipoprotein cholesterol (HDLc) (3.7%, p < 0.05) and serum osteocalcin (10.2%, p < 0.025). Significant decreases were observed in total cholesterol:HDLc ratios (5.5%, p < 0.006) and mean urinary N-telopeptide excretion (13.9%, p < 0.02). Urinary excretion of total isoflavones was negatively correlated with very-low-density lipoprotein cholesterol, triglycerides, and total cholesterol:HDLc ratios (p < 0.04). No significant changes from baseline in HDLc peroxidation, total cholesterol, triglycerides, low-density lipoprotein cholesterol, very-low-density lipoprotein cholesterol, bone-specific alkaline phosphatase, follicle-stimulating hormone, or estradiol levels were observed. CONCLUSIONS: Dietary inclusion of whole soy foods containing 60 mg/d of isoflavones results in significant serum levels of phytoestrogens and reductions in several key clinical risk factors for CVD and osteoporosis in normal postmenopausal women. Long-term, placebo-controlled clinical trials are needed to evaluate the effect of phytoestrogens on the clinical endpoints of CVD and osteoporosis in this population. Editor's comment*: The notable finding from this study is that estrogen deficient women who are not taking ERT (estrogen replacement therapy), may benefit from the inclusion of 3 servings of soy foods daily to reduce risk factors for both cardiovascular disease and osteoporosis. This level of soy foods taken over a period of 3 months provided antioxidant effects to protect cholesterol from being oxidized and raised HDL-cholesterol (the protective type). These are important outcomes since heart disease is the biggest killer of post-menopausal women. In addition, osteocalcin, a marker of bone formation was increased while NTX, a marker of bone degradation, was decreased suggesting possible bone protective benefits. Although isoflavone supplements are currently being marketed to post-menopausal women to help manage menopausal symptoms, the authors of this study chose to use whole soy foods due to the greater variety of nutrients that would be provided and the wider range of likely benefits. Women selected the 3 servings of soy foods using a mix n' match approach during the day. One serving was equal to either 10 grams roasted soy nuts or 250mls soy drink#. While the findings of this study are promising for guarding the health of post-menopausal women, especially since there is poor compliance with the use of ERT, more placebo-controlled studies are required of longer duration to confirm these results. * Sue Radd, Member of the International Soy Advisory Board#The soy drink used was Sanitarium So Good, which was manufactured especially to contain no added calcium and minimize the interference of calcium in interpreting the bone effects of soy. Title: Soyfood intake during adolescence and subsequent risk of breast cancer among Chinese women. Editor's comment*: The Shanghai Breast Cancer Study is the first in the world to report that soy food intake during adolescence may strongly protect against breast cancer in adult life. Women who consumed the higher amounts of soy foods as adolescents had half the risk of breast cancer compared to women who consumed the lowest levels. Breast cancer risk also progressively decreased as the level of soy product intake increased e.g tofu, soy milk and other soy products. Dried legumes such as red beans and mung beans were less strongly linked with risk reduction while fresh legumes such as peas, beans, and string beans, which contain the lowest amounts of phytoestrogens, were not related to the risk of breast cancer. These findings are striking since women living in China are already a low risk population having breast cancer incidence rates that are six-fold lower than in Australian women. While the study cannot prove causality, it lends credence to recent studies in rats where short-term neonatal and prepubertal intake of soy protein or genistein (a phytoestrogen in soy) significantly reduced the risk of mammary cancer later in life induced by chemical carcinogens. The likelihood of soy phytoestrogens being involved in early programming of the breast to make it more resistant to breast cancer in adult life is currently being researched. This study highlights the importance of initiating cancer prevention strategies early in life. The intake of soybeans and other legumes is low in Australian and New Zealand adolescents. Dietary guidelines to reduce cancer risk recommend an increased intake of plant foods such as vegetables, fruits, wholegrains and legumes. These recommendations also apply to teenagers. * Sue Radd, Member of the International Soy Advisory BoardTitle: Exposure to soy-based formula in infancy and endocrinological and reproductive outcomes in young adulthood. Abstract: CONTEXT: A large body of evidence documents the role of phytoestrogens in influencing hormone-dependent states. Infants fed soy formula receive high levels of phytoestrogens, in the form of soy isoflavones, during a stage of development at which permanent effects are theoretically possible. However, a paucity of data exists on the long-term effects of infant soy formulas. OBJECTIVE: To examine the association between infant exposure to soy formula and health in young adulthood, with an emphasis on reproductive health. DESIGN, SETTING, AND PARTICIPANTS: Retrospective cohort study conducted from March to August 1999 among adults aged 20 to 34 years who, as infants, participated during 1965-1978 in controlled feeding studies conducted at the University of Iowa, Iowa City (248 were fed soy formula and 563 were fed cow milk formula during infancy). MAIN OUTCOME MEASURES: Self-reported pubertal maturation, menstrual and reproductive history, height and usual weight, and current health, compared based on type of formula exposure during infancy. RESULTS: No statistically significant differences were observed between groups in either women or men for more than 30 outcomes. However, women who had been fed soy formula reported slightly longer duration of menstrual bleeding (adjusted mean difference, 0.37 days; 95% confidence interval [CI], 0.06-0.68), with no difference in severity of menstrual flow. They also reported greater discomfort with menstruation (unadjusted relative risk for extreme discomfort vs no or mild pain, 1.77; 95% CI, 1.04-3.00). CONCLUSIONS: Exposure to soy formula does not appear to lead to different general health or reproductive outcomes than exposure to cow milk formula. Although the few positive findings should be explored in future studies, our findings are reassuring about the safety of infant soy formula. Editor's comment*: Although it's been known since 1987 that infants fed soy infant formulas receive high levels of isoflavones, questions about the long-term health and safety effects of these phytochemicals have only surfaced relatively recently. This large study is a world first in that it sought to find evidence of any delayed effects in young adults who had been fed soy infant formula as babies. No statistically significant differences were observed between those adults who had been fed soy infant formula as infants compared to those fed cow milk infant formula in more than 30 outcomes studied. The outcomes included the timing of puberty and pubertal maturation, fertility, cancer, reproductive organ disorders, hormonal disorders, libido dysfunction, sexual orientation and birth defects in the subjects' offspring. Women who were fed soy infant formula as infants, did report that their menstrual bleeding was 0.37 days longer and that they experienced greater discomfort with menstruation but it is uncertain as to what this finding means and whether it is clinically relevant, or whether it occurred by chance. In a study with over 30 variables it is expected that about two would be statistically significant simply due to chance. A strength of the study was that soy formula intake was assessed based on existing university feeding records rather than relying on the memory of subjects, which may have biased the results. Although the actual isoflavone content of the soy infant formulas was not measured, the authors expect this to be similar to the isoflavone content of soy formulas sold today, as manufacturing processes have changed very little over this time. Based on the reassuring findings of this study, Dr Brian Strom, the chief investigator has publicly stated: "the good news is that, for children that need formula, soy infant formula is as safe as cow milk formula". Breast milk however remains the gold standard, and should continue to be promoted as the best choice over any formula. * Sue Radd, Member of the International Soy Advisory Board Title: Dietary phytoestrogens and their effect on bone: evidence from in vitro and in vivo, human observational, and dietary intervention studies Abstract: Impressive data from the many studies on cultured bone cells and rat models of postmenopausal osteoporosis support a significant bone-sparing effect of the soy isoflavones genistein and daidzein. Translating this research to the clinic has been more challenging, and thus far only a few clinical studies have attempted to tease out the influence of phytoestrogens on bone from the many other components of the diet. Human studies have shown promising although variable results. Studies have been mostly of short duration and with relatively small sample sizes, making it difficult to observe significant and accurate changes in bone. Levels of intake of the soy protein and isoflavones are varied, and the optimal isoflavone intake for bone-sparing effects remains to be determined. Clinical studies thus far performed can be broadly divided into those that have assessed biochemical evidence of reduced bone turnover from measurement of surrogate markers of osteoblast and osteoclast activity, and those that have examined changes in bone mineral density. There are no studies examining effects on fracture rate. This review focuses specifically on the potential influence of phytoestrogens on bone by examining the evidence from 17 in vitro studies of cultured bone cells, 24 in vivo studies of animal models for postmenopausal osteoporosis, 15 human observational/epidemiologic studies, and 17 dietary intervention studies. On balance, the collective data suggest that diets rich in phytoestrogens have bone-sparing effects in the long term, although the magnitude of the effect and the exact mechanism(s) of action are presently elusive or speculative. Editors comment*: The search for natural alternatives to estrogen is at an all time high, given the reluctance of women to take HRT (for fear of breast cancer) and the escalating rates of osteoporosis in Australia and other ageing Western countries. By the year 2020, one in three hospital beds will be occupied by elderly women with fractures, according to the Garvin Institute. Of all natural therapies under investigation, phytoestrogens appear to be the most promising. This review paper is timely, and provides a comprehensive overview of the effect of phytoestrogens from soy and other plant foods on bone. Convincing data is presented from test tube studies and animal models of postmenopausal osteoporosis, that dietary phytoestrogens prevent bone loss. Studies on humans are currently too few to draw final conclusions, but the data is provocative. Of note, is a two year Danish study showing prevention of bone loss in post-menopausal women who consumed two cups of phytoestrogen-rich soy milk daily. Some important issues are raised. First, what happens if you start to consume phytoestrogens early in life, and perhaps at a lower dose (as consumed in traditional Asian diets) rather than the relatively higher doses used in short-term research studies? One study on breast cancer in Chinese women found that those who consumed the highest amounts of soy during adolescence had the lowest risk of this cancer in adulthood. Second, the authors point out that people may gain varying degrees of benefit from soy. New findings from the Danish study mentioned above show that people who are able to produce 'equol', from consuming soy foods, gain the strongest bone benefits. Equol is a phytoestrogen made in the intestines by the action of intestinal bacteria on one isoflavone found in soy - but not everyone makes equol. While researchers investigate the exact mechanisms and just how effective phytoestrogens are in protecting our bones, it would seem reasonable and potentially beneficial to include soy foods in the diet as part of a range of lifestyle habits thought to be important in reducing the risk of osteoporosis. These include being physically active, not smoking, not drinking alcohol (or limiting the amount if you do), getting enough calcium, vitamin D and vitamin K, eating plenty of vegetables (especially green), cutting down on salt, eating less animal protein and minimising caffeine intake from coffee, cola and 'high energy' soft drinks. * Sue Radd, Member of the International Soy Advisory Board Title: Soy food consumption is associated with lower risk of coronary heart disease in Chinese women. Abstract: Soy food intake has been shown to have beneficial effects on cardiovascular disease risk factors. Data directly linking soy food intake to clinical outcomes of cardiovascular disease, however, are sparse. We examined the relationship between soy food intake and incidence of coronary heart disease (CHD) among participants in the Shanghai Women's Health Study, a population-based prospective cohort study of 75,000 Chinese women aged 40-70 y at the baseline survey that was conducted from 1997 to 2000. Included in this study were 64,915 women without previously diagnosed CHD, stroke, cancer and diabetes at baseline. Information on usual intake of soy foods was obtained at baseline through an in-person interview using a validated food-frequency questionnaire. Cohort members were followed biennially through in-person interviews. After a mean of 2.5 y (162,277 person-years) of follow-up, 62 incident cases of CHD (43 nonfatal myocardial infarctions and 19 CHD deaths) were documented. There was a clear monotonic dose-response relationship between soy food intake and risk of total CHD (P for trend = 0.003) with an adjusted relative risk (RR) of 0.25 (95% CI, 0.10-0.63) observed for women in the highest vs. the lowest quartile of total soy protein intake. The inverse association was more pronounced for nonfatal myocardial infarction (RR = 0.14; 95% CI, 0.04-0.48 for the highest vs. the lowest quartile of intake; P for trend = 0.001). This study provides, for the first time, direct evidence that soy food consumption may reduce the risk of CHD in women. Editors comment*: Many studies have demonstrated that soy foods can reduce key risk factors for heart disease, such as high blood cholesterol. However, this is the first showing that healthy Chinese women with the highest intake of soy products have the lowest risk of non-fatal heart disease - the type where you have a heart attack but survive. Women who consumed the most soy (equivalent to about 2 cups soy milk per day) had an 86 per cent lower risk of developing heart disease compared to women who consumed the least (about ½ cup soy milk per day). The strengths of the study are that it was conducted on a large number of women, and especially those who represent a high and diverse intake of soy foods, such as soy milk, tofu and other processed soy foods available in China. Further, the use of face-to-face interviews and a validated (road-tested) dietary questionnaire help make the results more reliable. An intriguing finding is that soy seems to guard against heart disease quite separately to the protection afforded by fish, tea, Vitamin E and other multivitamins, which are also believed to impact on heart disease risk. A limitation is that results are currently only available for a short follow-up period, namely 2.5 years. However, the authors are planning to run the study for at least 15 to 20 years so future results will be of interest. The findings are of great relevance to Australian women, and people from other western countries, where cardiovascular disease remains the nations biggest killer. The authors believe their study provides the strongest argument to date for the American Heart Association recommendation to increase soy food intake to promote heart health. Including soy milk on your cereal each morning and a tofu burger (or other soy food) at night may be a highly effective way to guard against heart attack. * Sue Radd, Member of the International Soy Advisory Board Title: Effects of a dietary portfolio of cholesterol-lowering foods vs Lovastatin on serum lipids and C-reactive protein. Abstract: CONTEXT: To enhance the effectiveness of diet in lowering cholesterol, recommendations of the Adult Treatment Panel III of the National Cholesterol Education Program emphasize diets low in saturated fat together with plant sterols and viscous fibers, and the American Heart Association supports the use of soy protein and nuts. OBJECTIVE: To determine whether a diet containing all of these recommended food components leads to cholesterol reduction comparable with that of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins). DESIGN: Randomized controlled trial conducted between October and December 2002. SETTING AND PARTICIPANTS: Forty-six healthy, hyperlipidemic adults (25 men and 21 postmenopausal women) with a mean (SE) age of 59 (1) years and body mass index of 27.6 (0.5), recruited from a Canadian hospital-affiliated nutrition research center and the community. INTERVENTIONS: Participants were randomly assigned to undergo 1 of 3 interventions on an outpatient basis for 1 month: a diet very low in saturated fat, based on milled whole-wheat cereals and low-fat dairy foods (n = 16; control); the same diet plus lovastatin, 20 mg/d (n = 14); or a diet high in plant sterols (1.0 g/1000 kcal), soy protein (21.4 g/1000 kcal), viscous fibers (9.8 g/1000 kcal), and almonds (14 g/1000 kcal) (n = 16; dietary portfolio). MAIN OUTCOME MEASURES: Lipid and C-reactive protein levels, obtained from fasting blood samples; blood pressure; and body weight; measured at weeks 0, 2, and 4 and compared among the 3 treatment groups. RESULTS: The control, statin, and dietary portfolio groups had mean (SE) decreases in low-density lipoprotein cholesterol of 8.0% (2.1%) (P =.002), 30.9% (3.6%) (P<.001), and 28.6% (3.2%) (P<.001), respectively. Respective reductions in C-reactive protein were 10.0% (8.6%) (P =.27), 33.3% (8.3%) (P =.002), and 28.2% (10.8%) (P =.02). The significant reductions in the statin and dietary portfolio groups were all significantly different from changes in the control group. There were no significant differences in efficacy between the statin and dietary portfolio treatments. CONCLUSION: In this study, diversifying cholesterol-lowering components in the same dietary portfolio increased the effectiveness of diet as a treatment of hypercholesterolemia. Editors comment*: While dietary intervention should be the first line of therapy before drugs are offered to treat high blood cholesterol, typical cholesterol lowering diets result in only a modest reduction in cholesterol of 4-13 per cent. The important finding of this new study is that an intensive dietary approach (dubbed the 'portfolio diet') can lower blood cholesterol just as effectively (by about 30 per cent) as the starting dose of a statin - the most commonly used drug for treating high cholesterol. In other words, scientific evidence now exists that the right type of diet can rival a drug approach! In addition to being low in saturated fat/cholesterol, the portfolio diet includes cholesterol lowering foods to provide sufficient amounts of soy protein, plant sterols, soluble fibre, as well as almonds each day. The US Food and Drug Administration permits separate health claims that such foods reduce heart disease risk by lowering blood cholesterol. But according to this Canadian study it is the combination of these foods that provides the most powerful approach. The authors estimated that the portfolio diet could reduce the risk of coronary heart disease by around 25 per cent! While this study has some clear limitations - it was conducted in a relatively small number of people and only for a short period - the findings are good news. This is particularly true for those who are highly motivated, cannot tolerate statins or choose lifestyle medicine over a drug approach. However, further research is needed to see whether the portfolio diet can be recommended for widespread use, because apart from having high blood cholesterol the subjects were otherwise healthy. Also, it will be important to find out if people can manage this type of diet on their own and stick to it for more than four weeks. Soy is a valuable food that complements many other beneficial foods in lowering high blood cholesterol. * Sue Radd, Member of the International Soy Advisory Board
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