The Journal of Nutrition Supplement: Soy Summit—Exploration of the Nutrition and Health Effects of Whole Soy Insights Gained from 20 Years of Soy Research

Soyfoods have long been recognized for their high-protein and low-saturated fat content, but over the past 20 y an impressive amount of soy-related research has evaluated the role of these foods in reducing chronic disease risk. Much of this research has been undertaken because the soybean is essentially a unique dietary source of isoflavones, a group of chemicals classified as phytoestrogens. The estrogen-like properties of isoflavones have also raised concern, however, that soyfoods might exert adverse effects in some individuals. There is intriguing animal and epidemiologic evidence indicating that modest amounts of soy consumed during childhood and/or adolescence reduces breast cancer risk. Evidence also suggests that soy reduces prostate cancer risk and inhibits prostate tumor metastasis, but additional clinical support for the chemopreventive effects of soyfoods is needed. Soy protein is modestly hypocholesterolemic and there is suggestive epidemiologic evidence that soyfoods lower risk of coronary heart disease (CHD) independent of effects on cholesterol. In clinical studies, soy favorably affects multiple CHD risk factors; however, with the exception of improved endothelial function, the data are too limited and/or inconsistent to allow definitive conclusions to be made. In regard to bone health, although recent clinical data have not supported the skeletal benefits of isoflavones, 2 large prospective epidemiologic studies found soy intake is associated with marked reductions in fracture risk. Soybean isoflavones also modestly alleviate hot flashes in menopausal women. Finally, other than allergic reactions, there is almost no credible evidence to suggest traditional soyfoods exert clinically relevant adverse effects in healthy individuals when consumed in amounts consistent with Asian intake. J. Nutr. 140: 2289S–2295S, 2010. Introduction A mere 2 decades ago, unless their client or patient was a vegetarian, health professionals had little reason to know much about the health attributes of soyfoods, perhaps other than that they were good sources of protein. No longer is this the case. The popularity of foods made from the soybean, which have been consumed for centuries in many Asian countries, has increased markedly in the United States and other Western countries. This increased popularity has occurred largely because of consumer belief that soyfoods may confer health benefits independent of their nutrient content. Soyfoods also appeal to those interested in eating a plant-based diet for ethical and environmental reasons, the latter of which is gaining scientific support (1). Nevertheless, the role of soyfoods in an overall healthy diet has become somewhat of a confusing and contentious issue in recent years. Understanding and interpreting the enormous amount of soy research conducted is challenging, because it requires understanding the strengths and weaknesses of a wide variety of experimental models and designs. The extent to which inconsistencies in the literature result from soy product-specific effects is a matter of much discussion (2). These products range from isolated soybean constituents such as isoflavones to “whole soyfoods,” although there is no uniform definition of the latter. 2 Author disclosure: M. Messina owns a consulting company whose clients include those who manufacture and/or sell soyfoods, soy protein, or isoflavone supplements. He also received travel costs and an honorarium from a nonrestricted educational grant provided by Pharmavite LLC to Columbia University for the Soy Summit, which served as the basis for this article. The grant provided funding for the summit and also covered the cost of this journal supplement. 1 Published in a supplement to The Journal of Nutrition. Presented at the conference, “Soy Summit: Exploration of the Nutrition and Health Effects of Whole Soy,” held in New York, NY, September 21–22, 2009. The conference was organized by the Institute of Human Nutrition, Columbia University, through an unrestricted educational grant from Pharmavite, LLC. The supplement coordinators for this supplement are Sharon R. Akabas, Columbia University, and Connie M. Weaver, Purdue University. Supplement Coordinator disclosure: S. Akabas and C. Weaver received travel costs and an honorarium from a nonrestricted educational grant provided by Pharmavite LLC to Columbia University for the Soy Summit, which served as the basis for this supplement. The grant provided funding for the summit and also covered the cost of this journal supplement. Connie M. Weaver serves on Pharmavite’s Advisory Board. The Guest Editor for this supplement is Neil Shay. Guest Editor Disclosure: Neil Shay declares no conflict of interest. The supplement is the responsibility of the guest editors to whom the Editor of The Journal of Nutrition has delegated supervision of both technical conformity to the published regulations of The Journal of Nutrition and general oversight of the scientific merit of each article. Publication costs for this supplementwere defrayed in part by the payment of page charges. This publication must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact. The opinions expressed in this publication are those of the authors and are not attributable to the sponsors or the publisher, Editor, or Editorial Board of The Journal of Nutrition. * To whom correspondence should be addressed. E-mail: markm@olympus.net. ã 2010 American Society for Nutrition. 2289S First published online October 27, 2010; doi:10.3945/jn.110. 124107. by gest on D ecem er 1, 2011 jn.nition. org D ow nladed fom Most soy research has focused on isoflavones and soy protein. However, not only may other soybean components exert important health effects, but there is the potential for interactions among the various components to result in outcomes difficult to predict from knowledge of the individual soybean components (3). Clearly, however, in some cases, the health effects of soyfoods are ascribed to specific components. The perceived inconsistency between findings from Asian epidemiologic studies, which are generally viewed as supportive of health benefits, and the clinical studies, which are viewed as being less so, is commonly cited as an example of soy products differentially affecting health outcomes. The epidemiologic data are based on the intake of traditional soyfoods, such as tofu, miso, and soymilk, whereas the intervention products almost exclusively have been isolated soy protein (ISP; by definition ISP is $90% protein) and soy isoflavone supplements. However, even if one accepts that a discrepancy between the epidemiologic and clinical datasets exists, there are explanations aside from differences in the chemical composition of the soy products in question that might account for this inconsistency. These include the timing and duration of exposure and ethnic differences in response to soy. There is also the possibility that the Asian epidemiologic studies are simply identifying a “healthy user effect” and not a direct effect of soy intake. Soyfoods and the Dietary Guidelines That the soybean (Glycine max) is a legume can be overlooked, because for the most part it is not consumed directly as the bean, as are most legumes, but rather as already noted, in the form of foods such as tofu, soymilk, tempeh, and miso. These foods have little obvious physical resemblance to the native bean. Even edamame or green (immature) soybeans look and taste more like a vegetable than a legume. Soy protein products such as soy protein concentrate, ISP, and soy flour are even less likely to conjure up images of beans. Legumes are an underutilized food source in the United States despite their being included in the Dietary Guidelines in both the meat and bean group and the vegetable group. Soyfoods represent a convenient way to meet the legume recommendation and for this reason alone their consumption can be encouraged. The Dietary Guidelines recommend consuming 3 cups (6 servings or ~540 g) of legumes per week, but few Americans meet that goal. Data from the NHANES 1999–2002 revealed that only 7.9% of the adult population consumed beans, peas, or lentils on any given day (4). Europeans (5) and North Americans (6) typically get only a fraction of their protein from legumes, which contrasts with the situation in Asian countries, such as Japan (7), andmany central and SouthAmerican countries, such asNicaragua and Brazil in particular (8). In addition to protein, legumes are excellent sources of fiber, resistant starch, and certain vitamins and minerals such as folate and potassium, the latter of which is a nutrient of concern (9). U.S. potassium intake is only about one-half the dietary recommended intake (10). In addition, many legumes also have a very high antioxidant content, with oxygen radical absorbance capacity values equaling those of fruits touted for their antioxidant activity (11). Also, despite their high-carbohydrate content, the glycemic load of beans is relatively low because of their low glycemic index (12). There is arguably some question about the extent to which some soy protein products mimic legumes in a way that warrants their classification in the vegetable group (e.g. they are low in soluble fiber). But clearly both the traditional soyfoods and the soy protein products are excellent sources of protein. In fact, compared with other legumes, soybeans are much higher in protein (13) and the quality of soy protein is superior (protein digestibility correct amino acid scores typically range between 0.9 and 1.0) (14). Not unexpectedly, given the high protein digestibility corrected amino acid scores, the digestibility of soy protein is quite high, typically $90%, and the indispensible amino acid concentration (mg/g protein) of soy protein exceeds the dietary requirements (15). Soybeans are also much higher in fat (;40% of total energy) (13) than most