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      Guidance from an NIH Workshop on Designing, Implementing, and Reporting Clinical Studies of Soy Interventions1–4

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          Abstract

          The NIH sponsored a scientific workshop, “Soy Protein/Isoflavone Research: Challenges in Designing and Evaluating Intervention Studies,” July 28–29, 2009. The workshop goal was to provide guidance for the next generation of soy protein/isoflavone human research. Session topics included population exposure to soy; the variability of the human response to soy; product composition; methods, tools, and resources available to estimate exposure and protocol adherence; and analytical methods to assess soy in foods and supplements and analytes in biologic fluids and other tissues. The intent of the workshop was to address the quality of soy studies, not the efficacy or safety of soy. Prior NIH workshops and an evidence-based review questioned the quality of data from human soy studies. If clinical studies are pursued, investigators need to ensure that the experimental designs are optimal and the studies properly executed. The workshop participants identified methodological issues that may confound study results and interpretation. Scientifically sound and useful options for dealing with these issues were discussed. The resulting guidance is presented in this document with a brief rationale. The guidance is specific to soy clinical research and does not address nonsoy-related factors that should also be considered in designing and reporting clinical studies. This guidance may be used by investigators, journal editors, study sponsors, and protocol reviewers for a variety of purposes, including designing and implementing trials, reporting results, and interpreting published epidemiological and clinical studies.

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          Most cited references95

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          Estimated Asian adult soy protein and isoflavone intakes.

          There is substantial interest in the possible anticancer effects of soy foods. In part, this is because of the historically low incidence rates of breast and prostate cancer in Asia. Of the several putative soybean chemopreventive agents, isoflavones have received the most attention. Awareness of this research has led increasing numbers of consumers to use soy foods, isoflavone-fortified foods, and isoflavone supplements. Therefore, there is a need for guidance regarding appropriate isoflavone intake levels. To this end, this article analyzed soy protein (as a surrogate for isoflavones) and isoflavone intake of the major soy food-consuming countries using individual dietary surveys for the bulk of the information. In total, 24 surveys from 4 countries that met the inclusion criteria were identified: Japan (n = 11), China (n = 7), Hong Kong (n = 4), and Singapore (n = 2). The results indicate that older Japanese adults consume approximately 6-11 g of soy protein and 25-50 mg of isoflavones (expressed as aglycone equivalents) per day. Intake in Hong Kong and Singapore is lower than in Japan, whereas significant regional intake differences exist for China. Evidence suggests that < or =10% of the Asian population consumes as much as 25 g of soy protein or 100 mg of isoflavones per day. The applicability of these findings for making soy intake recommendations for non-Asians is discussed.
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            Evidence for lack of absorption of soy isoflavone glycosides in humans, supporting the crucial role of intestinal metabolism for bioavailability.

            The isoflavones daidzein and genistein occur naturally in most soyfoods, conjugated almost exclusively to sugars. Controversy exists regarding the extent of bioavailability of isoflavone glycosides, and the mechanism of intestinal absorption of isoflavones in humans is unclear. Evidence from intestinal perfusion and in vitro cell culture studies indicates that isoflavone glycosides are poorly absorbed, yet isoflavones are bioavailable and appear in high concentrations in plasma, irrespective of whether they are ingested as aglycones or glycoside conjugates. The objective was to determine whether isoflavone glycosides are absorbed from the intestine intact and reach the peripheral circulation unchanged. Plasma was collected at timed intervals before and after healthy adults ingested 50 mg of one of the isoflavone beta-glycosides (daidzin or genistin) or 250 mL soymilk containing mainly isoflavone glycosides. Electrospray ionization mass spectrometry was used to detect daidzin and genistin after solid-phase extraction of these conjugates from plasma. Bioavailability of isoflavones was confirmed by gas chromatography-mass spectrometry analysis. Specific and sensitive electrospray mass spectrometry failed to detect even traces of daidzin or genistin in plasma collected 1, 2, and 8 h after their ingestion as pure compounds or in a soyfood matrix. However, plasma was enriched in isoflavones that were hydrolyzable with a combined beta-glucuronidase and sulfatase enzyme preparation. Isoflavone glycosides are not absorbed intact across the enterocyte of healthy adults, and their bioavailability requires initial hydrolysis of the sugar moiety by intestinal beta-glucosidases for uptake to the peripheral circulation.
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              Phytoestrogen content of foods consumed in Canada, including isoflavones, lignans, and coumestan.

              Phytoestrogens may play a role in hormone-related diseases such as cancer, but epidemiological and clinical data are conflicting in part due to inadequate databases used in intake estimation. A database of nine phytoestrogens in foods relevant to Western diets was developed to more accurately estimate intakes. Foods (N = 121) available in Ontario, Canada were prepared as commonly consumed and analyzed for isoflavones (genistein, daidzein, glycitein, formononetin), lignans (secoisolariciresinol, matairesinol, pinoresinol, lariciresinol), and coumestan (coumestrol) using gas chromatography-mass spectrometry methods. Data were presented on an as is (wet) basis per 100 g and per serving. Food groups with decreasing levels of total phytoestrogens per 100 g are nuts and oilseeds, soy products, cereals and breads, legumes, meat products, and other processed foods that may contain soy, vegetables, fruits, alcoholic, and nonalcoholic beverages. Soy products contain the highest amounts of isoflavone, followed by legumes, meat products and other processed foods, cereals and breads, nuts and oilseeds, vegetables, alcoholic beverages, fruits, and nonalcoholic beverages. Decreasing amounts of lignans are found in nuts and oilseeds, cereals and breads, legumes, fruits, vegetables, soy products, processed foods, alcoholic, and nonalcoholic beverages. The richest sources of specific phytoestrogens, including coumestrol, were identified. The database will improve phytoestrogen intake estimation in future epidemiological and clinical studies particularly in Western populations.
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                Author and article information

                Journal
                J Nutr
                jnutr
                The Journal of Nutrition
                American Society for Nutrition
                0022-3166
                1541-6100
                June 2010
                June 2010
                : 140
                : 6
                : 1192S-1204S
                Affiliations
                [5 ]Office of Dietary Supplements,; [6 ]National Center for Complementary and Alternative Medicine,; [7 ]National Cancer Institute, and [8 ]Division of Nutrition Research Coordination, National Institutes of Health, Bethesda, MD 20892; [9 ]Department of Nutrition, Loma Linda University, Loma Linda, CA 92350; [10 ]Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration, College Park, MD 20740; [11 ]Department of Nutritional Sciences, University of Toronto, Toronto, Ontario, Canada M5S 3E2; [12 ]Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, AR 72202; [13 ]Department of Foods and Nutrition, Purdue University, West Lafayette, IN 47907
                Author notes
                [* ]To whom correspondence should be addressed. E-mail: kleinm@ 123456mail.nih.gov .
                [14]

                Current address: Office of Dietary Supplements, NIH, 6100 Executive Boulevard, Room 3B01, Bethesda, MD 20892.

                Article
                121830
                10.3945/jn.110.121830
                2869505
                20392880
                b9292730-3b6a-4a1e-84f6-1195c7d809aa
                Copyright © 2010, American Society for Nutrition
                History
                Categories
                Supplement: Guidance from an NIH Workshop on Designing, Implementing, and Reporting Clinical Studies of Soy Interventions

                Nutrition & Dietetics
                Nutrition & Dietetics

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