image: University of Toronto professor Laura Chiavaroli (left) and PhD student Gabrielle Viscardi
Credit: University of Toronto
A University of Toronto study is providing reassuring evidence about the consumption of soy foods in women* who are postmenopausal.
The analysis of 40 randomized controlled trials in over 3,000 participants found that estrogen-like compounds in soy had no effect on key markers of estrogen-related cancers, supporting its safety as both a food and potential therapy.
Several health advocacy groups including the Canadian Cardiovascular Society already recommend soy foods as part of a healthy diet. They are a high quality and complete source of protein and are recognized by several national governmental health agencies — including Health Canada and the US Food and Drug Administration — as effective in reducing the risk of heart disease. Soy foods have also been shown to alleviate hot flashes associated with menopause, which affect many women and impact their quality of life.
“The risk of cardiovascular disease increases substantially as women go through menopause, so soy can offer dual benefits during this particular phase of life,” says Laura Chiavaroli, the study’s senior author and an assistant professor of nutritional sciences at U of T’s Temerty Faculty of Medicine.
Yet she notes that many people are hesitant to eat soy foods because they contain estrogen-like compounds called isoflavones, which are naturally found in plants and have a similar structure to the hormone estrogen. In animal studies, large doses of isoflavones have been linked to a higher risk of cancer.
“Something we hear very often is that people have a lot of concern about consuming soy because there are so many conflicting messages out there,” says Gabrielle Viscardi, a second-year PhD student in the department of nutritional sciences and the study’s lead author.
In their systematic review and meta-analysis, published in Advances in Nutrition, the researchers gathered results from trials that compared the effects of soy isoflavones on four different biological outcomes related to risk for endometrial and other female-related cancers. Those outcomes included the thickness of the uterus lining, the vaginal maturation index — a measure of estrogen status within the vaginal environment — and levels of circulating estrogen and follicle-stimulating hormone.
The trials followed postmenopausal women from around the world who had consumed either soy isoflavones or a non-isoflavone control for at least three months.
After assessing the risk of bias and quality of the evidence, the researchers concluded that consumption of soy isoflavones did not affect these four estrogen-related markers. Their findings support the idea that soy isoflavones behave differently from human estrogen, particularly when it comes to cancers that depend on estrogen to develop.
“We have estrogen receptors throughout our bodies but, contrary to the hormone estrogen, isoflavones from soy don’t bind to all the estrogen receptors equally,” says Viscardi, who is also a registered dietitian.
“That’s why we see a beneficial effect on the cardiovascular system and no effect on the female reproductive system.”
This difference in biological activity explains why soy isoflavones have been considered as a possible alternative to hormone replacement therapy (HRT), which is used to treat menopause symptoms by replacing the estrogen that the body stops producing during this period.
Chiavaroli, who is also an affiliate scientist at the Li Ka Shing Knowledge Institute of St. Michael’s Hospital, Unity Health Toronto, notes that some people do not want to take HRTs and are seeking alternative options.
Further, HRTs may also not be a good option for people at an increased risk of estrogen-sensitive cancers like breast cancer, as well as those with a history of heart disease and stroke. For these individuals, consuming soy foods as part of a balanced diet could help manage their menopausal symptoms while also reducing their risk for cardiovascular disease.
Chiavaroli says the study findings also align with Health Canada’s dietary guidelines that encourage people to choose plant-based proteins more often, a move that would also convey benefits for the environment.
“We hope our study will help people feel more comfortable including soy foods in their diet without being concerned that it’s going to increase their risk of estrogen-dependent cancer,” says Chiavaroli.
*Although menopause is sex-specific, we use the term women here to reflect the original study and the published trials it references. We recognize that some persons experiencing menopause may identify differently than with this gender.
This study was funded by the United Soybean Board (United States Department of Agriculture) and the Canadian Institutes of Health Research through the Canada-wide Human Nutrition Trialists’ Network.
Journal
Advances in Nutrition
Method of Research
Systematic review
Subject of Research
People
Article Title
Effect of Soy Isoflavones on Measures of Estrogenicity: A Systematic Review and Meta-Analysis of Randomized Controlled Trials
Article Publication Date
27-Nov-2024
COI Statement
AZ is a part-time research associate at INQUIS Clinical Research Ltd, a contract research organization, and has received consulting fees from Glycemic Index Foundation. TAK has received research support from the Canadian Institutes of Health Research (CIHR), the International Life Science Institute (ILSI), and National Honey Board. He has been an invited speaker at the Calorie Control Council Annual meeting for which he has received an honorarium. He has received funding from the Toronto 3D Knowledge Synthesis and Clinical Trials foundation. MM was employed by the Soy Nutrition Institute Global, an organization that receives funding from the United Soybean Board (USB) and from members involved in the soy industry. CWCK has received grants or research support from the Advanced Food Materials Network, Agriculture and Agri-Foods Canada (AAFC), Almond Board of California, Barilla, Canadian Institutes of Health Research (CIHR), Canola Council of Canada, International Nut and Dried Fruit Council, International Tree Nut Council Research and Education Foundation, Loblaw Brands Ltd, the Peanut Institute, Pulse Canada, and Unilever. He has received in-kind research support from the Almond Board of California, Barilla, California Walnut Commission, Kellogg Canada, Loblaw Companies, Nutrartis, Quaker (PepsiCo), the Peanut Institute, Primo, Unico, Unilever, and WhiteWave Foods/Danone. He has received travel support and/or honoraria from the Barilla, California Walnut Commission, Canola Council of Canada, General Mills, International Nut and Dried Fruit Council, International Pasta Organization, Lantmannen, Loblaw Brands Ltd., Nutrition Foundation of Italy, Oldways Preservation Trust, Paramount Farms, the Peanut Institute, Pulse Canada, Sun-Maid, Tate & Lyle, Unilever, and White Wave Foods/Danone. He has served on the scientific advisory board for the International Tree Nut Council, International Pasta Organization, McCormick Science Institute, and Oldways Preservation Trust. He is a founding member of the International Carbohydrate Quality Consortium (ICQC), Executive Board Member of the Diabetes and Nutrition Study Group (DNSG) of the European Association for the Study of Diabetes (EASD), is on the Clinical Practice Guidelines Expert Committee for Nutrition Therapy of the EASD, and is a Director of the Toronto 3D Knowledge Synthesis and Clinical Trials foundation. DJAJ has received research grants from Saskatchewan & Alberta Pulse Growers Associations, the Agricultural Bioproducts Innovation Program through the Pulse Research Network, the Advanced Foods and Material Network, Loblaw Companies Ltd., Unilever Canada and Netherlands, Barilla, the Almond Board of California, Agriculture and Agri-food Canada, Pulse Canada, Kellogg’s Company, Canada, Quaker Oats, Canada, Procter & Gamble Technical Centre Ltd., Bayer Consumer Care, Springfield, NJ, Pepsi/Quaker, International Nut & Dried Fruit Council (INC), Soy Foods Association of North America, the Coca-Cola Company (investigator initiated, unrestricted grant), Solae, Haine Celestial, the Sanitarium Company, Orafti, the International Tree Nut Council Nutrition Research and Education Foundation, the Peanut Institute, Soy Nutrition Institute (SNI), the Canola and Flax Councils of Canada, the Calorie Control Council, the Canadian Institutes of Health Research (CIHR), the Canada Foundation for Innovation (CFI), and the Ontario Research Fund (ORF). He has received in-kind supplies for trials as a research support from the Almond Board of California, Walnut Council of California, the Peanut Institute, Barilla, Unilever, Unico, Primo, Loblaw Companies, Quaker (Pepsico), Pristine Gourmet, Bunge Limited, Kellogg Canada, and WhiteWave Foods. He has been on the speaker’s panel, served on the scientific advisory board and/or received travel support and/or honoraria from Nutritional Fundamentals for Health (NFH)-Nutramedica, Saint Barnabas Medical Center, The University of Chicago, 2020 China Glycemic Index (GI) International Conference, Atlantic Pain Conference, Academy of Life Long Learning, the Almond Board of California, Canadian Agriculture Policy Institute, Loblaw Companies Ltd, the Griffin Hospital (for the development of the NuVal scoring system), the Coca-Cola Company, Epicure, Danone, Diet Quality Photo Navigation (DQPN), Better Therapeutics (FareWell), Verywell, True Health Initiative (THI), Heali AI Corp, Institute of Food Technologists (IFT), Soy Nutrition Institute (SNI), Herbalife Nutrition Institute (HNI), Saskatchewan & Alberta Pulse Growers Associations, Sanitarium Company, Orafti, the International Tree Nut Council Nutrition Research and Education Foundation, the Peanut Institute, Herbalife International, Pacific Health Laboratories, Barilla, Metagenics, Bayer Consumer Care, Unilever Canada and Netherlands, Solae, Kellogg, Quaker Oats, Procter & Gamble, Abbott Laboratories, Dean Foods, the California Strawberry Commission, Haine Celestial, PepsiCo, the Alpro Foundation, Pioneer Hi-Bred International, DuPont Nutrition and Health, Spherix Consulting and WhiteWave Foods, the Advanced Foods and Material Network, the Canola and Flax Councils of Canada, Agri-Culture and Agri-Food Canada, the Canadian Agri-Food Policy Institute, Pulse Canada, the Soy Foods Association of North America, the Nutrition Foundation of Italy (NFI), Nutra-Source Diagnostics, the McDougall Program, the Toronto Knowledge Translation Group (St. Michael's Hospital), the Canadian College of Naturopathic Medicine, The Hospital for Sick Children, the Canadian Nutrition Society (CNS), the American Society of Nutrition (ASN), Arizona State University, Paolo Sorbini Foundation, the Institute of Nutrition, Metabolism and Diabetes, the Lawson Centre Nutrition Digital Series, and the 19th Annual Stare-Hegsted Lecture. He received an honorarium from the United States Department of Agriculture to present the 2013 W.O. Atwater Memorial Lecture. He received the 2013 Award for Excellence in Research from the International Nut and Dried Fruit Council. He received funding and travel support from the Canadian Society of Endocrinology and Metabolism to produce mini cases for the Canadian Diabetes Association (CDA). He is a member of the International Carbohydrate Quality Consortium (ICQC). His wife, Alexandra L Jenkins, is a director and partner of INQUIS Clinical Research for the Food Industry, his 2 daughters, Wendy Jenkins and Amy Jenkins, have published a vegetarian book that promotes the use of the foods described here, The Portfolio Diet for Cardiovascular Risk Reduction (Academic Press/Elsevier 2020 ISBN:978-0-12-810510-8), and his sister, Caroline Brydson, received funding through a grant from the St. Michael’s Hospital Foundation to develop a cookbook for one of his studies. He is also a vegan. JLS has received research support from the Canadian Foundation for Innovation, Ontario Research Fund, Province of Ontario Ministry of Research and Innovation and Science, Canadian Institutes of health Research (CIHR), Diabetes Canada, American Society for Nutrition (ASN), International Nut and Dried Fruit Council (INC) Foundation, National Honey Board (U.S. Department of Agriculture [USDA] honey “Checkoff” program), Institute for the Advancement of Food and Nutrition Sciences (IAFNS; formerly ILSI North America), Pulse Canada, Quaker Oats Center of Excellence, The United Soybean Board (USDA soy “Checkoff” program), Protein Industries Canada (a Government of Canada Global Innovation Clusters), The Tate and Lyle Nutritional Research Fund at the University of Toronto, The Glycemic Control and Cardiovascular Disease in Type 2 Diabetes Fund at the University of Toronto (a fund established by the Alberta Pulse Growers), The Plant Protein Fund at the University of Toronto (a fund which has received contributions from IFF), and The Nutrition Trialists Network Research Fund at the University of Toronto (a fund which has received donations from the Calorie Control Council, Physicians Committee for Responsible Medicine, and vegan grants through the Karuna Foundation). He has received food donations to support randomized controlled trials from the Almond Board of California, California Walnut Commission, Peanut Institute, Barilla, Unilever/Upfield, Unico/Primo, Loblaw Companies, Quaker, Kellogg Canada, Danone, Nutrartis, Soylent, and Dairy Farmers of Canada. He has received travel support, speaker fees and/or honoraria from ASN, Danone, Dairy Farmers of Canada, FoodMinds LLC, Nestlé, Abbott, General Mills, Nutrition Communications, International Food Information Council (IFIC), Calorie Control Council, International Sweeteners Association, International Glutamate Technical Committee, Arab Beverages Association, and Phynova. He has or has had ad hoc consulting arrangements with Perkins Coie LLP, Tate & Lyle, Inquis Clinical Research, Ingredion, and Brightseed. He is a former member of the European Fruit Juice Association Scientific Expert Panel and a former member of the Soy Nutrition Institute (SNI) Scientific Advisory Committee. He is on the Clinical Practice Guidelines Expert Committees of Diabetes Canada, European Association for the study of Diabetes (EASD), Canadian Cardiovascular Society (CCS), and Obesity Canada/Canadian Association of Bariatric Physicians and Surgeons. He serves as an unpaid member of the Board of Trustees of IAFNS and formerly served as an unpaid scientific advisor for the Carbohydrates Committee of IAFNS. He is a Director at Large of the Canadian Nutrition Society (CNS), a founding member of the International Carbohydrate Quality Consortium (ICQC), an Executive Board Member of the Diabetes and Nutrition Study Group (DNSG) of the EASD, and a director of the Toronto 3D Knowledge Synthesis and Clinical Trials foundation. His spouse is an employee of AB InBev. LC has received research support from Protein Industries Canada (a Government of Canada Global Innovation Clusters), Alberta Pulse Growers, The United Soybean Board (USDA soy “Checkoff” program), and the Canadian Institutes of Health Research (CIHR). All other authors report no conflicts of interest to disclose.