Soya and health 2002 – clinical evidence, dietetic applications

On May 30–31 2002, an International Soya and Health Conference was held at the Queen Elizabeth Centre in London. Leading experts from all over the world were brought together to discuss the findings of soya research and focus on health-related topics. This report highlights some of the presentations. The conference provided academics, physicians, dieticians, nutritionists and representatives from the food industry with an opportunity to debate new research findings and to discuss how they may impact on dietary intakes. Speakers covered various aspects of soya in the diet and its health implications. Topics included soya protein and effects on hypertension and heart disease; soya and breast cancer; soya and women's health; the role of soya saponins; soya and vegetarian diets in renal disease and the effect of soya on bone loss and memory. Professor Cesare Sirtori from the University of Milan, Italy, discussed the value of a soya protein diet in the treatment of paediatric hypercholesterolemia. An Italian study with pre-pubertal children found a reduction in cholesterolemia of around 25% after substituting 20 g/day of animal protein with soya protein. He stated that lower cholesterolemia and lower coronary risk in populations consuming soya support the hypothesis that this diet may result in coronary prevention. Extensive research in this area has resulted in the American Food and Drug Administration granting approval of a claim for soya proteins for coronary prevention via cholesterol reduction. Mechanism(s) of action has not been defined regarding cholesterol regulation. Cholesterol balance studies in patients have indicated that cholesterol reduction is not associated with increased cholesterol/bile acid excretion. The suggestion that isoflavones present in soya may regulate cholesterolemia, has not been unequivocally established. It is likely that a combination of components working together in soya result in depression of cholesterol levels. Dr Helen Wiseman, of King's College, London, discussed the role of soya and the mechanisms of vascular protection. She felt that although cholesterol lowering is probably the best-documented cardioprotective effect of soya, vascular protection is also likely to contribute and may be mediated via a number of mechanisms including effects on arterial function, cellular effects and oestrogen receptor-mediated effects. Another mechanism of vascular protection of soya is thought to be its antioxidant properties. The oxidative modification of LDL is important in the pathogenesis of atherosclerotic lesions. Thus, inhibiting oxidation of LDL should decrease and prevent atherosclerosis. Metabolism of isoflavones: importance of equol, Professor Kenneth Setchell, of the Children's Hospital Medical Centre, USA, presented evidence from his research suggesting that the beneficial effects of isoflavones are dependent on the ability of the body to convert them into a metabolite known as equol. Equol is exclusively a product of intestinal bacterial metabolism of daidzein, one of the two main isoflavones found in abundance in soybeans and most soya foods. Equol possesses significant oestrogenic activity having affinity for both oestrogen receptors. Equol is far more potent as an oestrogen and is superior to all other isoflavones in its antioxidant activity. Professor Setchell highlighted that it is now apparent that there are two distinct subpopulations of people and that ‘bacterio-typing’ individuals for their ability to make equol may hold the clue to the effectiveness of soya protein diets in the treatment or prevention of hormone-dependent conditions. He suggested identifying equol producing individuals as a possible way forward for the future, and estimated that over 70% of the Japanese, compared with 30–50% of US, and probably UK, populations were producers. Given subjects are either ‘equol-producers’ or ‘non-equol producers’, Professor Setchell suggested that this could explain some of the variance in reported data in previous clinical studies on the health benefits of soya on bone, vasomotor symptoms of menopause, and lipid-lowering. According to recent studies, equol-producers generally consume a diet lower in saturates and higher in carbohydrates. However, it is important to note that equol-producers can only produce equol if they consume daidzein and must consume soya in the diet. Given that antibiotics can affect the production of equol, another question was raised: can diet, functional foods or drugs manipulate equol production? Current research shows pre and/or probiotic foods could possibly introduce the appropriate bacteria to the gut to produce equol however, knowledge in this area is limited and requires further investigation. Professor Barbara Meyers, from the University of Wollongong, Australia, discussed the hypercholesterolemic effect of chronic soya consumption and suggested that it may be linked to equol. Her research group examined the cardiovascular health benefits of foods containing whole soybean extracts containing soya protein, soya isoflavones and polyunsaturated fatty acids including alpha-linolenic (n-3) acid. A total of 26 mildly hypercholesterolemic and/or hypertensive volunteers were randomised in a placebo-controlled crossover trial to consume 4 servings a day of either soya-based milk and yoghurt or equivalent dairy products for 5 weeks, followed by the alternative foods for a further 5 weeks. In 23 subjects who completed the study, whole soya supplementation increased plasma and urinary isoflavone levels 23 and 6-fold, respectively, but there were no overall differences in plasma lipids, blood pressure or arterial compliance between the soya and dairy diets. Retrospective analysis, however, revealed that in eight equol-positive subjects, there were highly significant reductions of total cholesterol (8.5%), LDL-cholesterol (10%), LDL: HDL ratio (13.5%), plasma triglycerides (21%) and lipoprotein(a) (11%) with the soya diet. It appears that regular consumption of whole soybean foods improves plasma lipids in equol-positive subjects. This has led to the suggestion that equol may contribute to the hypercholesterolemic effect of soya consumption. Research shows that regular consumption of soya products has a cholesterol-lowering effect; however, the relative importance of specific components of whole soya in mediating health benefits is still unclear. Professor Mark Messina, of Loma Linda University, VA, USA, discussed the role soya might play in reducing the rate of breast cancer. Initial investigations into the low breast cancer mortality rate in Asia led to beliefs that soya might play a role in reducing breast cancer. This was supported by animal work indicating isoflavones inhibited mammary tumour development, and the potential for weak oestrogens to exert anti-estrogenic effects. Research shows there are multiple ways in which soya may reduce breast cancer risk including hormonal and non-hormonal mechanisms. However, Dr Messina concluded that there is little epidemiological data to support the notion that the adult consumption of soya reduces post-menopausal breast cancer and only modestly suggests that it is protective against pre-menopausal breast cancer. Eva Lydeking-Olsen reported on the findings from her research at the Institute for Optimum Nutrition. She reported her study as being amongst the first to explore the beneficial role of the complete soya bean in the form of soymilk, on bone health in post-menopausal women. The research found consumption of soymilk to be protective towards bone mineral content and density. The study was initiated by her concerns over the potential decrease in quality of life, as a result of the ageing population. Poor bone health in post-menopausal women may lead to an inability to work thus greater reliance on the government for health and financial support. The aim of the study was to evaluate the effect on plasma lipoproteins and tolerance of 2 years consumption of soymilk (400–500 mL daily) supplying 14–17.5 g dietary protein per day, the use of transdermal progesterone (25 mg/day), or both, on bone mineral density. Two soymilk preparations were used: one with intact soya protein and a high isoflavone content (100 mg isoflavones per day) prepared from whole soybeans, and one prepared from alcohol-extracted soya protein free of isoflavones. Two transdermal preparations were tested, one with and one without progesterone. The results drew the following conclusions; isoflavone-rich soymilk prevented bone loss in the lumbar spine and transdermal progesterone had a bone-sparing effect in postmenopausal women. Soymilk, in the absence of progesterone, increased HDL-cholesterol. The isoflavone-rich soymilk reduced LDL-cholesterol and the total cholesterol/HDL-cholesterol ratio. Progesterone combined with either of the soymilk preparations decreased LDL-cholesterol and the total cholesterol/HDL-cholesterol ratio. The combined treatment, isoflavone-rich soymilk plus progesterone, showed a negative interaction, resulting in bone-loss to a greater extent than either treatment alone, but less pronounced than placebo. Professor Venket Rao, from the University of Toronto, Canada, discussed the possible beneficial effects of soya saponins on human health. Although once thought of as ‘anti-nutrients’, they are now believed to be beneficial. They have been shown to have anti-carcinogenic, hypercholesterolemic and immune stimulatory properties in animal models. Saponins are present in many plants, with soybeans constituting the major source of dietary saponins. He presented data to illustrate an inverse relationship between the consumption of soybeans and saponins and the incidence of several chronic diseases. Prevention of chronic disease requires increased consumption of plant food, i.e. fruit, vegetables, cereals and legumes. Thus, generally a diet low in fat, high in fibre and micronutrients, is required. During his presentation, Professor Roa outlined the challenges he has faced in studying soya saponins. There are several different saponins and they constitute less than one per cent of the soybean. Problems include a lack of saponin standards, large amounts of purified saponins being required for intervention studies and the sophisticated HPLC techniques required to isolate saponins. Biological properties of saponins include bitter tastes, natural surfactant, cell hemolysis, growth retardation, lower nutrient availability and decreased enzyme activity. Professor Roa predicts that saponins will play an important role in diabetes, cardiovascular disease and cancers, e.g. colorectal. However, the significance of dietary soya saponins in human health needs to be established. Their use as drugs and/or functional foods was also discussed. Professor Sandra File, from King's College, London, spoke about soya and its effects on human memory. Her presentation included the findings of two recent studies suggesting that soya can improve human cognition. In the first study, 27 male and female students were randomly allocated to receive a supervised diet that was either low (0.5 mg total isoflavones/day) or high (100 mg total isoflavones/day) in isoflavones for 10 weeks. Subjects completed a battery of cognitive tests at baseline and after 10 weeks of diet. Those receiving the high isoflavone diet showed significantly greater improvements than those on the low isoflavone diet in short- and long-term memory and in mental flexibility. These improvements were found in both the men and women. The second study was a double-blind study in which 33 post-menopausal women were randomly allocated to placebo or soya supplements (Solgen, 60 mg/day total isoflavone equivalents). Subjects completed a series of cognitive tests at baseline and after 12 weeks of supplements. Those receiving Solgen showed significantly greater improvements in episodic memory, in mental flexibility and in ability to plan, than did those on placebo. The results of these two studies suggest that soya can improve cognition in both men and women, and in both a younger and older age group. The pattern of cognitive benefits suggests that the isoflavones were having significant effects in the hippocampus and frontal cortex. Although the results were significant, Professor File highlighted there is still a need to find out the long-term effects of soya, and the differences from dietary and supplementary sources. With the majority of presentations focusing on the clinical application of soya, Mr Karl Weingartner, of University of Illinois, USA, discussed the development of the soya industry. He outlined the various products that can be made from soya, changes in the methods of soya processing, and the explosion of new soya foods in the marketplace. Until recently, only large companies have processed soya. These companies’ products were often used as a protein source for animal feed and as an ingredient to improve the functional properties of foods. In the 1990s, the soya industry in North America underwent some significant changes. The mid-1990s heralded several innovative medium-scale processes for both dry and wet soy processing and in October 1999, the American Food and Drug Administration (FDA) allowed a health claim for soya protein. These changes resulted in the development of soya foods intended for consumers at large. The soybean is a nutritious, versatile product. The functional properties of soya include water absorption, emulsification and texture. Soybeans are processed into soya flour (50% protein), soya protein concentrate (70% protein) and isolated soya protein (90% protein). The defatted soya flour is generally used in weaning food, gruel, cookies, crackers, muffins, breads, cereals, cakes, doughnuts, pastas, dry mixes, tortillas, pancakes, pizza dough and ground meat. Textured vegetable protein, often used for vegetarian food and as an ingredient with ground meat for patties and sausages, generally has a 12-month shelf life. Soya concentrate is used in meat products, baked goods and speciality items. Soya isolate is used as an ingredient in high-protein foods including dairy, as a milk replacement and nutritional supplements (bodybuilding drinks and energy bars). Green soybeans, which are harvested earlier, can be frozen as a vegetable, either in pods or shelled. Jacqui Lynas, dietician for the Family Heart Association, suggested the recommended intake of 25 g of soya protein on a daily basis is quite a challenge to the majority of people in the UK, yet the intake is feasible and possible owing to the range of products available on the market. Products soon to appear on the supermarket shelves include peanut butter, soya burgers, ethnic foods, smoothies and flavoured tofu. In 1996, the UK government's scientific advisory committee, the Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment (COT) was asked for a view on the public health implications of dietary phytoestrogens. The COT expressed concern over the potential for phytoestrogens to cause adverse effects, particularly in infants fed soya-based infant formula. However, at the time the COT was unable to reach a conclusion due to insufficient information. In 2000, the COT established a working group to review the data from the research programme and the scientific literature to assess the risks and benefits of dietary phytoestrogens to human health. Tom Barlow, from the Food Standards Agency, London, discussed the working group's review and the problems faced when interpreting the data. The Working Group addressed the following key points: on the basis of current evidence, does ingestion of soya-based infant formula pose any risk for human infants; are there health implications to other subgroups of the population from the ingestion of dietary phytoestrogens; to consider the evidence for beneficial effects of dietary estrogens; to make recommendations for further research. The COT aim to publish a report of the group's findings in autumn 2002. Tanya Carr, a nutrition consultant in the UK, discussed the process of obtaining a health claim for soya in the UK via the Joint Health Claims Initiative (JHCI). In July 2002 a health claim for soya was approved by the JHCI and states: ‘the inclusion of at least 25 g of soya protein per day, as part of a diet low in saturated fat, can help reduce blood cholesterol levels.’ (http:www.jhci.co.uk) Products that wish to use this claim must contain at least 6.25 g of soya protein per serving and must retain naturally occurring isoflavones. For full details visit the website.

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