Soy Health and Nutrition Research

Hundreds of peer-reviewed studies focused on the safety and health benefits of soyfoods and soybean components have been published over the past three decades. Through the Soy Health and Nutrition Research Program, funded by the United Soybean Board, the Soy Nutrition Institute has supported research on priority health outcomes. Current and recent SNI research initiatives are noted below.

Research projects (in progress):
• Soy Protein and Metabolic Syndrome
• Soybean Oil and Cardiometabolic Health
• Clinical Effects of Soy on Skin Health (research underway)
• “Soybean oil consumption does not lead to a pro-inflammatory or pro-oxidative state” (expected publication: Spring 2021)

Recent Research Published in Peer-Reviewed Journals

SOY ISOFLAVONES

Title: Neither soyfoods nor isoflavones warrant classification as endocrine disruptors: a technical review of the observational and clinical data
Journal:  Critical Reviews in Food Science and Nutrition
Authors:  Mark Messina, Sonia Blanco Mejia, Aedin Cassidy, Alison Duncan, Mindy Kurzer, Chisato Nagato, Martin Ronis, Ian Rowland, John Sievenpiper, Stephen Barnes
Date published in journal: 2021 (available online March 2021)
Citation: Mark Messina, Sonia Blanco Mejia, Aedin Cassidy, Alison Duncan, Mindy Kurzer, Chisato Nagato, Martin Ronis, Ian Rowland, John Sievenpiper & Stephen Barnes (2021) Neither soyfoods nor isoflavones warrant classification as endocrine disruptors: a technical review of the observational and clinical data, Critical Reviews in Food Science and Nutrition, DOI: 10.1080/10408398.2021.1895054
ABSTRACT:
Soybeans are a rich source of isoflavones, which are classified as phytoestrogens. Despite numerous proposed benefits, isoflavones are often classified as endocrine disruptors, based primarily on animal studies. However, there are ample human data regarding the health effects of isoflavones. We conducted a technical review, systematically searching Medline, EMBASE, and the Cochrane Library (from inception through January 2021). We included clinical studies, observational studies, and systematic reviews and meta-analyses (SRMA) that examined the relationship between soy and/or isoflavone intake and endocrine-related endpoints. 417 reports (229 observational studies, 157 clinical studies and 32 SRMAs) met our eligibility criteria. The available evidence indicates that isoflavone intake does not adversely affect thyroid function. Adverse effects are also not seen on breast or endometrial tissue or estrogen levels in women, or testosterone or estrogen levels, or sperm or semen parameters in men. Although menstrual cycle length may be slightly increased, ovulation is not prevented. Limited insight could be gained about possible impacts of in utero isoflavone exposure, but the existing data are reassuring. Adverse effects of isoflavone intake were not identified in children, but limited research has been conducted. After extensive review, the evidence does not support classifying isoflavones as endocrine disruptors.

SOY AND TESTOSTERONE

Title: Neither soy nor isoflavone intake affects male reproductive hormones: An expanded and updated meta-analysis of clinical studies
Journal: Reproductive Toxicology
Authors: Katharine E. Reed, Juliana Camargo, Jill Hamilton-Reeves, Mindy Kurzer, Mark Messina
Date published in journal: March 2021 (available online December 2020)
Citation: Reed KE, Camargo J, Hamilton-Reeves J, et al. Neither soy nor isoflavone intake affects male reproductive hormones: An expanded and updated meta-analysis of clinical studies. Reprod Toxicol. 2021;100:60-7.
ABSTRACT:
Concerns that the phytoestrogens (isoflavones) in soy may feminize men continue to be raised. Several studies and case-reports describing feminizing effects including lowering testosterone levels and raising estrogen levels in men have been published. For this reason, the clinical data were meta-analyzed to determine whether soy or isoflavone intake affects total testosterone (TT), free testosterone (FT), estradiol (E2), estrone (E1), and sex hormone binding globulin (SHBG). PubMed and CAB Abstracts databases were searched between 2010 and April 2020, with use of controlled vocabulary specific to the databases. Peer-reviewed studies published in English were selected if (1) adult men consumed soyfoods, soy protein, or isoflavone extracts (from soy or red clover) and [2] circulating TT, FT, SHBG, E2 or E1 was assessed. Data were extracted by two independent reviewers. With one exception, studies included in a 2010 meta-analysis were included in the current analysis. A total of 41 studies were included in the analyses. TT and FT levels were measured in 1753 and 752 men, respectively; E2 and E1 levels were measured in 1000 and 239 men, respectively and SHBG was measured in 967 men. Regardless of the statistical model, no significant effects of soy protein or isoflavone intake on any of the outcomes measured were found. Sub-analysis of the data according to isoflavone dose and study duration also showed no effect. This updated and expanded meta-analysis indicates that regardless of dose and study duration, neither soy protein nor isoflavone exposure affects TT, FT, E2 or E1 levels in men.

FOOD ALLERGIES

Title: Recent surveys on food allergy prevalence
Journal: Nutrition Today
Authors: Mark Messina and Carina Venter
Date published in journal: January/February 2020
Citation: Messina M & Venter C (2020) Recent surveys on food allergy prevalence. Nutr Today 55, 22-29.
ABSTRACT:
Substantial numbers of children and adults report having immunoglobulin E–mediated food allergies. However, generating accurate food allergy prevalence data is difficult. Self-reported data can overestimate prevalence when compared with prevalence estimates established by more rigorous methods. As of 2004, in the United States, the Food Allergen Labeling and Consumer Protection Act mandated that the label should declare the source of the food if the product contains that food or a protein-containing ingredient from that food (not all proteins in a major food allergen cause allergic reactions) in the manner described by the law. The 8 major food allergens are milk, eggs, fish, crustacean shellfish, tree nuts, peanuts, wheat, and soybeans, commonly referred to as the “Big 8.” These 8 allergens are thought to account for 90% of the food allergy reactions. Recently published large surveys of Americans and Canadian adults and children provide considerable insight into the prevalence of allergy for the major allergens. These data indicate that there is a large variation in prevalence among the Big 8. The prevalence of soybeans allergy is lower than the prevalence reported for each of the other 7 major allergens, which has been used to argue that soy could be removed from the Big 8 without risking harm to the public. However, the momentum appears to be in favor of expanding the Big 8. The US Food and Drug Administration is evaluating classification of sesame seed as a major allergen; it is already classified as a major allergen in Canada, Australia, and Europe. Europe classifies 14 foods as major allergens. There may be some advantage to standardizing major allergen lists globally, although it may be equally important to acknowledge differences in priority allergens based on cultural and dietary preferences. It is incumbent upon health professionals to help their patients and clients identify foods to which they are allergic and aid in planning diets that are nutritionally adequate despite
elimination of these foods.

CHOLESTEROL-LOWERING EFFECT OF SOY

Title: Cumulative meta-analysis of the soy effect over time
Journal: Journal of the American Heart Association
Authors: David J. A. Jenkins, Sonia Blanco Mejia, Laura Chiavaroli, Effie Viguiliouk, Siying S. Li, Cyril W. C. Kendall, Vladmir Vuksan, and John L. Sievenpiper
Date published in journal: July 2019
Citation: Jenkins DJA, Blanco Mejia S, Chiavaroli L et al. (2019) Cumulative meta-analysis of the soy effect over time. Journal of the American Heart Association 8, e012458.
ABSTRACT:
Soy protein foods have attracted attention as useful plant protein foods with mild cholesterol-lowering effects that are suitable for inclusion in therapeutic diets. But on the basis of the lack of consistency in significant cholesterol reduction by soy in 46 randomized controlled trials, the US Food and Drug Administration (FDA) is reassessing whether the 1999 heart health claim for soy protein should be revoked.
Methods and Results: We have, therefore, performed a cumulative meta-analysis on the 46 soy trials identified by the FDA to determine if at any time, since the 1999 FDA final rule that established the soy heart health claim, the soy effect on serum cholesterol lost significance. The cumulative meta-analysis for both total cholesterol and low-density lipoprotein cholesterol demonstrated preservation of the small, but significant, reductions seen both before and during the subsequent 14 years since the health claim was originally approved. For low-density lipoprotein cholesterol, the mean reduction in 1999 was -6.3 mg/dL (95% CI, -8.7 to -3.9 mg/dL; P=0.00001) and remained in the range of -4.2 to -6.7 mg/dL ( P=0.0006 to P=0.0002, respectively) in the years after 1999. At no time point did the total cholesterol or low-density lipoprotein cholesterol reductions lose significance or were the differences at individual time points in the cumulative meta-analysis significantly different from those seen in 1999 when the health claim was approved.
Conclusions: A cumulative meta-analysis of the data selected by the FDA indicates continued significance of total cholesterol and low-density lipoprotein cholesterol reduction after soy consumption and supports the rationale behind the original soy FDA heart health claim.

SOY PROTEIN HEALTH CLAIM

Title: A meta-analysis of 46 studies identified by the FDA demonstrates that soy protein decreases circulating LDL and total cholesterol concentrations in adults
Journal: The Journal of Nutrition
Authors: Sonia Blanco Mejia, Mark Messina, Siying S. Li, Effie Viguiliouk, Laura Chiavaroli, Tauseef A. Khan, Korbua Srichaikul, Arash Mirrahimi, John L. Sievenpiper, Penny Kris-Etherton, and David J. A. Jenkins
Date published in journal: June 2019
Citation: Blanco Mejia S, Messina M, Li SS et al. (2019) A meta-analysis of 46 studies identified by the FDA demonstrates that soy protein decreases circulating LDL and total cholesterol concentrations in adults. J. Nutr. 149, 968-981
ABSTRACT:
Certain plant foods (nuts and soy protein) and food components (viscous fibers and plant sterols) have been permitted by the FDA to carry a heart health claim based on their cholesterol-lowering ability. The FDA is currently considering revoking the heart health claim for soy protein based on the tentative conclusion that the scientific evidence currently available does not support its previous determination that there is significant scientific agreement. We performed a meta-analysis of the 46 controlled trials on which the FDA will base its decision to revoke the heart health claim for soy protein.
Methods and Results: We included the 46 trials on adult men and women, with baseline circulating LDL cholesterol concentrations ranging from 110 to 201 mg/dL, as identified by the FDA, that studied the effects of soy protein on LDL cholesterol and total cholesterol (TC) compared with non-soy protein. Two independent reviewers extracted relevant data. Data were pooled by the generic inverse variance method with a random effects model and expressed as mean differences with 95% CI. Heterogeneity was assessed and quantified. Of the 46 trials identified by the FDA, 43 provided data for meta-analyses. Of these, 41 provided data for LDL cholesterol, and all 43 provided data for TC. Soy protein at a median dose of 25 g/d during a median follow-up of 6 wk decreased LDL cholesterol by 4.76 mg/dL (95% CI: -6.71, -2.80 mg/dL, P < 0.0001; I2 = 55%, P < 0.0001) and decreased TC by 6.41 mg/dL (95% CI: -9.30, -3.52 mg/dL, P < 0.0001; I2 = 74%, P < 0.0001) compared with non-soy protein controls. There was no dose-response effect or evidence of publication bias for either outcome. Inspection of the individual trial estimates indicated most trials ( approximately 75%) showed a reduction in LDL cholesterol (range: -0.77 to -58.60 mg/dL), although only a minority of these were individually statistically significant.
Conclusions: Soy protein significantly reduced LDL cholesterol by approximately 3-4% in adults. Our data support the advice given to the general public internationally to increase plant protein intake. This trial was registered at clinicaltrials.gov as NCT03468127.

SOY AND PUBERTY

Title: Soy isoflavone consumption and age at pubarche in adolescent males
Journal: European Journal of Nutrition
Authors: Gina Segovia Siapco, Peter Pribis, Keiji Oda, and Joan Sabaté
Date published in journal: September 2018
Citation: Segovia-Siapco G, Pribis P, Oda K et al. (2018) Soy isoflavone consumption and age at pubarche in adolescent males. Eur. J. Nutr. 57, 2287-2294.
ABSTRACT:
Isoflavones have estrogenic properties that may adversely affect pubertal development of boys. We examined if soy isoflavone consumption is associated with age at pubarche (first onset of pubic hair) in a male population with a wide range of soy intake.
Methods and Results: Boys aged 12-18 years (n = 248) who attended schools around Adventist universities in Southern California and Michigan self-reported their age at pubarche. Intake of soy isoflavones was assessed using a validated Web-based food frequency questionnaire; consumption levels were designated as low, moderate, and high. Descriptives, time-to-event analysis, and Cox proportional hazards regression that controlled for confounders were performed. Energy-adjusted mean intakes were 0.8-54.9 mg/d for total isoflavones, 0.4-22.1 mg/d for daidzein, and 0.4-28.0 mg/d for genistein. Moderate and high total soy isoflavone intake were significantly associated with earlier adjusted median age at pubarche: 12.58 years [RR (95% CI): 1.58 (1.06, 2.36)] for moderate and 12.50 years [RR (95% CI): 1.63 (1.03, 2.60)] for high vs. 13.00 years for low consumers. Similarly, daidzein and genistein consumption was also significantly associated with age at pubarche. No significant associations were found for facial hair for any of the isoflavones.
Conclusions: Age at pubarche in this male population widely exposed to soy is within the reported range for boys’ pubarcheal age; moderate/high consumers tend to have it earlier compared to low consumers. Further studies are needed to ascertain that substantial exposure to soy isoflavones does not adversely affect pubertal development of boys.

SOY AND RESISTANCE TRAINING

Title: No difference between the effects of supplementing with soy protein versus animal protein on gains in muscle mass and strength in response to resistance exercise
Journal: International Journal of Sport Nutrition and Exercise Metabolism
Authors: Mark Messina, Heidi Lynch, Jared M. Dickinson, and Katharine E. Reed
Date published in journal: January 2018
Citation: Messina M, Lynch H, Dickinson JM et al. (2018) No difference between the effects of supplementing with soy protein versus animal protein on gains in muscle mass and strength in response to resistance exercise. International journal of sport nutrition and exercise metabolism 28, 674-685.
ABSTRACT:
Much attention has been given to determining the influence of total protein intake and protein source on gains in lean body mass (LBM) and strength in response to resistance exercise training (RET). Acute studies indicate that whey protein, likely related to its higher leucine content, stimulates muscle protein synthesis to a greater extent than proteins such as soy and casein. Less clear is the extent to which the type of protein supplemented impacts strength and LBM in long-term studies (>/=6 weeks). Therefore, a meta-analysis was conducted to compare the effect of supplementation with soy protein to animal protein supplementation on strength and LBM in response to RET. Nine studies involving 266 participants suitable for inclusion in the meta-analysis were identified. Five studies compared whey with soy protein, and four studies compared soy protein with other proteins (beef, milk, or dairy protein). Meta-analysis showed that supplementing RET with whey or soy protein resulted in significant increases in strength but found no difference between groups (bench press: chi(2) = 0.02, p = .90; squat: chi(2) = 0.22, p = .64). There was no significant effect of whey or soy alone (n = 5) on LBM change and no differences between groups (chi(2) = 0.00, p = .96). Strength and LBM both increased significantly in the “other protein” and the soy groups (n = 9), but there were no between-group differences (bench: chi(2) = 0.02, p = .88; squat: chi(2) = 0.78, p = .38; and LBM: chi(2) = 0.06, p = .80). The results of this meta-analysis indicate that soy protein supplementation produces similar gains in strength and LBM in response to RET as whey protein.


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