Introduction to and perspectives from the Fifth International Symposium on the Role of Soy in Preventing and Treating Chronic Disease.

The proceedings from the First International Symposium on the Role of Soy in Preventing and Treating and Chronic Disease were published in this journal in 1995. For a decade this symposium has been the seminal gathering place for investigators and health professionals to discuss the latest research on the health effects of soy foods and soybean constituents. The conference this year attracted nearly 300 participants from 20 different countries. In total there were 200 oral and poster presentations. Certainly, this volume of research attests to the continued interest in soy and to the number and variety of laboratories working in this area. Although many questions regarding health effects remain unanswered, the extensive research underway provides cause for optimism that over the ensuing years some answers will become clear, or at least sufficiently clear so as to provide the foundation for conducting long-term randomized clinical trials that use clinical outcomes such as fractures and coronary events as endpoints. These trials are needed to definitely establish both efficacy and safety, although the long history of Asian soy food use and the existing literature of human clinical trials certainly support the latter. Not surprisingly, research into the health effects of soy in humans has consisted of mostly short-term trials involving relatively few subjects. Such studies have generally used intermediate markers of risk. A few small multiyear trials have also been conducted, and several large multiyear randomized clinical trials in the bone area are in progress. The nutrition literature is not without inconsistencies, and soy is no exception. There are many obvious reasons for the variation in study results, but one discussed throughout the symposium and addressed in part by Erdman et al. in these proceedings is the varied composition of soy products used in research. It is self-evident that differences in chemical composition among the different soy products can affect biological activity; however, the extent to which these products differ chemically may not have been previously appreciated. Clearly, isoflavone supplements devoid of protein differ from isoflavone-rich soy protein products, but isoflavone supplements can also differ markedly in their isoflavone profile and soy protein products differ markedly in their isoflavone content. Preliminary evidence presented at this symposium suggests that commercial processing of the soybean affects the structure of soy protein and the products of its intestinal digestion in humans. The significance of these observations is clear when considered along with emerging research suggesting that peptides of fairly long length can be absorbed and exert effects in vivo. For health outcomes thought to be primarily affected by soy protein, such as cholesterol reduction, it now seems important to establish how processing affects biological activity. It should be noted that most of the clinical research supporting health benefits of soy has involved the use of commercially processed soy proteins and not traditional soy foods. Recent research indicates that soy peptides can now be added to the list of potential bioactive components of soy. Peptides from proteins other than soy are also under investigation and we could ask whether intensified efforts on the effects of processing on the protein structure of other food proteins are warranted. Two other perspectives with potentially important implications for understanding the health effects of soy foods were discussed at this symposium. One was the issue of the variable actions of intestinal microflora on isoflavone glycones and their subsequent absorption and metabolism. Differences in microflora can markedly affect the amounts and types of isoflavones found in body tissues from person to person. Some of the inconsistencies reported in the literature may result from these differing serum isoflavone levels. Most importantly, only 30– 50% of the adult population possesses the intestinal bacteria capable of converting the soybean isoflavone daidzein into the isoflavonoid equol. Intriguing but still quite speculative data suggest that equol production is advantageous. Certainly, equol appears to have a number of unique actions. One recommendation from the symposium is that researchers consider analyzing data from studies according to equol status and consider stratifying subjects according to equol status when 1 Published in a supplement to The Journal of Nutrition. Presented as part of the Fifth International Symposium on the Role of Soy in Preventing and Treating Chronic Disease held in Orlando, FL, September 21–24, 2003. This conference was supported by The Solae Company; United Soybean Board; Archer Daniels Midland Company; Cargill Health and Food Technologies; Cargill Soy Protein Solutions; Dr. Chung’s Food Co., Ltd.; Illinois Soybean Association/Illinois Soybean Checkoff Board; Indiana Soybean Board; Nichimo International Inc.; Solbar Plant Extracts Ltd.; Soyatech, Inc.; Wyeth Consumer Healthcare; AOCS; DrSoy Nutrition; and Soyfoods Association of North America. Guest editors for this symposium were Mark Messina, John Erdman, and Kenneth D.R. Setchell. 2 To whom correspondence should be addressed. E-mail: markm@olympus.net.