You're in the middle of a conversation with friends or colleagues, when suddenly, an invisible wave of heat washes over you, leaving you flushed, sweaty, and utterly uncomfortable. Hot flashes, those unpredictable bursts of heat that disrupt your day and leave you feeling like you're standing in the Sahara desert, the hallmark of menopause.
Enter soy, the humble legume that's been making waves in the world of menopause management. With whispers of its potential to quell hot flashes and restore a sense of equilibrium, soy piqued my curiosity and beckoned me to delve deeper into its mysteries. Armed with a blend of scientific curiosity and personal determination, I embarked on a quest to uncover the truth behind soy's reputation as a menopause superhero.
In this blog, I invite you to join me on this journey of discovery as we navigate through the maze of menopause and explore the role of soy in taming those fiery foes known as hot flashes. Through research, we'll unravel the complexities of menopause, separate fact from fiction, and uncover practical strategies for finding relief and reclaiming our vitality. So, grab your favorite beverage (iced, of course, to combat those pesky hot flashes), and let's embark on this adventure together.
I donβt need to tell you that hot flashes are a common symptom of menopause, with roughly 60-90% of women in Western countries reporting hot flashes (termed vasomotor symptoms) (1,2). Yet if we were in an Asian country with high soy consumption hot flashes would not be all that common. In fact only 10-25% of menopausal women in Asian countries report having hot flashes. This is based on self-reported incidents so there could be some biases at play but still it is quite a stark contrast and makes you wonder why?
It is possible that the difference in rates of hot flashes could be due to diet. In particular the differences in the amount of soy products consumed. Soybeans and their products are particularly high in the phytochemical, isoflavone (3).
Isoflavones are able to exert estrogen like effects due to their ability to bind to estrogen receptors (ERs) (4). Therefore, isoflavones can be classed as phytoestrogens, or plant estrogens (4).
Soybeans and foods derived from soybean are the main foodstuffs which are able to provide physiologically relevant amounts of isoflavones, although red clover and alfalfa can also provide isoflavones. There are many types of isoflavone with soybeans containing 12 different types (5). There are 2 types of isoflavone supplements available on the market, and that have been used in clinical trials, the main difference is in their genistein (a form of isoflavone) content. One is made from whole soybeans so it is high in genistein and low in glycitein, whereas the other, which is made from the germ or hypocotyledon portion of the bean, is low in genistein and high in glycitein (6).
When isoflavones are ingested, enzymes in the gut alter their structure and then in some women, gut bacteria can further alter them to S-Equol which may have added benefits, a substance which has a similar structure to estrogen (7).
It is in the gut that we see other differences between women from Asian countries and their Caucasian counterparts. Less than about 25% of Caucasians have the bacteria to convert isoflavones all the way to S-equol conversely, over 50% of Asians have this bacteria (8). Research has found that for non-equol producers, even if they consume adequate amounts of isoflavone, the efficacy of alleviating menopausal symptoms may be limited (9). In an observational study of 364 women, only equol-producers benefited from dietary isoflavones for reducing vasomotor symptoms (10). A systematic review and meta-analysis of RCTs which assessed the efficacy of soy isoflavones and equol for alleviating menopausal symptoms (especially vasomotor symptoms) in postmenopausal women who were either equol producers or nonproducers showed the greater benefit of equol on hot flash scores (11).
As the conversion of isoflavones to S-equol is dependent on the type of gut bacteria it would seem logical that probiotics may be able to enhance s-equol production. However, research findings on the benefits of probitotics to enhance s-equol production are conflicting (12,13). This could be due to differences in the strains of probiotics used, indeed faecal cultures of equol-producing women, showed that the s-equol-producing bacteria include Lactococcus garvieae (14,15).
The simplest solution may be to supplement with s-equol, and s-equol supplementation in non-equol producers has been shown to successfully alleviated mood-related symptoms in menopausal women (16) and by a systematic review which concluded that supplementing with s-equol to s-equol nonproducers significantly lowered the incidence and/or severity of hot flashes in menopausal women (17).
There are ~3.5 mg isoflavones per gram of protein in traditional soy foods (18). One serving of a traditional soy food provides ~8 G protein and 25 mg isoflavones. Although processing can result in the loss of isoflavone content from soy products (19). See Isoflavones infographic.
Isoflavones only remain in our body for about 24 hours (20). Therefore, the highest sustained serum isoflavone concentrations are likely achieved by dividing daily isoflavone intake into several doses across the day, reflecting the dietary patterns of isoflavone intake from soy foods in Asia. Washburn et al. found splitting the dose of soy supplement to twice-daily decreased the severity of hot flashes more than giving the total amount in one dose, suggesting consistent circulating levels of phytoestrogens to be more effective (21). However it should be noted there is a large interindividual variation in isoflavone metabolism such that in response to the ingestion of similar amounts of isoflavones, (22,23).
Although research on isoflavone rich foods (eg, soy foods, soy protein, and supplements derived from soybeans and red clover) in relation to menopause symptoms has only relatively recently (1990βs) been investigated there have been a number of studies (23).
Cancellieri et al. found that using an herbal supplement containing 72 mg of isoflavones from soy beans and red clover for 6 months significantly reduced hot flashes (24). Another small-scale prospective study of 51 healthy postmenopausal women also found a 57% reduction in the frequency and severity of hot flashes after taking 60 mg of isoflavones daily for 12 weeks (25). Another study this time using soy nuts in place of a non-soy protein for 8 weeks, and found over 40% reduction in hot flashes (26). This was regardless of equol-producing status (26). A large meta-analysis (a review of all the published research) by BolaΓ±os et al (27) concluded that isoflavone products were efficacious at reducing hot flashes (28).
Another systematic review and meta-analysis by Taku et al (29), involved 13 trials (n = 1196 women) that evaluated frequency and 9 trials that evaluated severity (n = 988 women), of studies that intervened with supplements of isoflavones derived from soybeans only. In the overall analysis, the net (minus the placebo effect) decrease in frequency and severity in response to isoflavones was 20.62% (P = 0.00001) and 26.19% (P = 0.001), respectively. Trials lasting >12 weeks led to larger decreases than did trials that were shorter in duration.
Despite a dose response relationship between isoflavone intake and serum isoflavone concentrations (30,31). This does not translate into a dose-response relation between total isoflavone content and hot flash alleviation. However, the geinstein,a type of isoflavone, content of the supplement greatly influenced efficacy. In 2006, Williamson-Hughes et al (32) showed that isoflavone supplements that provided 15 mg geinstein were more likely to report a reduction in hot flashes than those supplements low in genistein. Taku et al (29) also found that studies providing genistein intakes above the median for all studies (18.8 mg/d), produced a net reduction in hot flash frequency ( 29.13% compared with a reduction of only 12.47% for supplements providing β€18.8 mg/d, p=0.03). Therefore, when consuming at least ~19 mg genistein/d one can anticipate an approximate 60% reduction in hot flash frequency.
A placebo effect is unavoidable, and may explain some of the findings from studies showing no benefit of isoflavones (33,34). Some but not all studies have reported gastrointestinal symptoms with isoflavone supplementation.
Finally, this data must be interpreted in the light that estrogen remains the most effective therapy for hot flashes (35). A study comparing 45 mg of isoflavones twice daily, with low-dose HRT (1 mg of estradiol and 0.5 mg of norethisterone acetate), and placebo using the Menopause Rating Scale, both treatments were superior to placebo, but HRT was superior to isoflavones (36). Therefore, isoflavones cannot totally replace traditional HRT in alleviating menopausal symptoms but could help.
Although there are no harmful effects of soy products on thyroid function in healthy individuals, it can interfere with a food consumption in healthy humans with the absorption of thyroid medication levothyroxine. Therefore, thyroxine medication should be taken on an empty stomach.
Isoflavones particularly ones high in Genistein i.e. those derived from the whole soybean, may be beneficial for attenuation of hot flashes. Aim to consume 19 mg/d genistein or 60 mg/d isoflavones about 20 g soy protein over the course of a day chronically > 12 weeks could reduce number and severity of hot flashes, consuming S-equol may also produce beneficial effects.
Information in this blog is for education purposes and you should consult your medical practitioner if you think you are having hot flashes.
This information is for educational purposes only. You should contact your healthcare professional before you make any dietary changes or use any supplements. Supplements may also be contaminated and care should be taken when using them.
1. Welty F.K., Lee K.S., Lew N.S., Nasca M., Zhou J.R. The association between soy nut consumption and decreased menopausal symptoms. J. Womens Health. 2007;16:361β369. doi: 10.1089/jwh.2006.0207.
2. Reed S.D., Lampe J.W., Qu C., Gundersen G., Fuller S., Copeland W.K., Newton K.M. Self-reported menopausal symptoms in a racially diverse population and soy food consumption. Maturitas. 2013;75:152β158. doi: 10.1016/j.maturitas.2013.03.003.
3. Franke AA, Custer LJ, Wang W, Shi CY. HPLC analysis of isoflavonoids and other phenolic agents from foods and from human fluids. Proc Soc Exp Biol Med, 217 (1998), pp. 263-273
4. Oseni T, Patel R, Pyle J, Jordan VC. Selective estrogen receptor modulators and phytoestrogens. Planta Med, 74 (2008), pp. 1656-1665
5. Murphy PA, Barua K, Hauck CC. Solvent extraction selection in the determination of isoflavones in soy foods. J Chromatogr B Analyt Technol Biomed Life Sci, 777 (2002), pp. 129-138
6. Setchell KD, Brown NM, Lydeking-Olsen E. The clinical importance of the metabolite equol-a clue to the effectiveness of soy and its isoflavones. J Nutr, 132 (2002), pp. 3577-3584
7. Tsourounis C. Clinical effects of phytoestrogens. Clin. Obstet. Gynecol. 2001;44:836β842. doi: 10.1097/00003081-200112000-00021.
8. Jackson RL, Greiwe JS, Schwen RJ. Emerging evidence of the health benefits of S-equol, an estrogen receptor beta agonist. Nutr Rev, 69 (2011), pp. 432-448
9. Jackson R.L., Greiwe J.S., Desai P.B., Schwen R.J. Single-dose and steady-state pharmacokinetic studies of S-equol, a potent nonhormonal, estrogen receptor Ξ²-agonist being developed for the treatment of menopausal symptoms. Menopause. 2011;18:185β193.
10. Newton K.M., Reed S.D., Uchiyama S., Qu C., Ueno T., Iwashita S., Gunderson G., Fuller S., Lampe J.W. A cross-sectional study of equol producer status and self-reported vasomotor symptoms. Menopause. 2015;22:489β495.
11. Daily J.W., Ko B.S., Ryuk J., Liu M., Zhang W., Park S. Equol decreases hot flashes in postmenopausal women: A systematic review and meta-analysis of randomized clinical trials. J. Med. Food. 2019;22:127β139.
12. Setchell K.D.R. The history and basic science development of soy isoflavones. Menopause. 2017;24:1338β1350.
13. Guadamuro L., Dohrmann A.B., Tebbe C.C., Mayo B., Delgado S. Bacterial communities and metabolic activity of faecal cultures from equol producer and non-producer menopausal women under treatment with soy isoflavones. BMC Microbiol. 2017;17:93.
14. Ishiwata N., Melby M.K., Mizuno S., Watanabe S. New equol supplement for relieving menopausal symptoms: Randomized, placebo-controlled trial of Japanese women. Menopause. 2009;16:141β148.
15. Daily J.W., Ko B.S., Ryuk J., Liu M., Zhang W., Park S. Equol decreases hot flashes in postmenopausal women: A systematic review and meta-analysis of randomized clinical trials. J. Med. Food. 2019;22:127β139.
16. Messina M, Nagata C, Wu AH. Estimated Asian adult soy protein and isoflavone intakes. Nutr Cancer, 55 (2006), pp. 1-12
17 Lin J, Padmanaban PG, Wang C. Retention of isoflavones and saponins during the processing of soy protein isolates. J Am Oil Chem Soc, 83 (2006), pp. 59-63
18. North American Menopause Society The role of soy isoflavones in menopausal health: Report of The North American Menopause Society/Wulf H. Utian Translational Science Symposium in Chicago, IL (October 2010) Menopause. 2011;18:732β753.
20. Rowland I, Faughnan M, Hoey L, Wahala K, Williamson G, Cassidy A Bioavailability of phyto-oestrogens. Br J Nutr, 89 (suppl 1) (2003), pp. S45-S58
21. Washburn S., Burke G.L., Morgan T., Anthony M. Effect of soy protein supplementation on serum lipoproteins, blood pressure, and menopausal symptoms in perimenopausal women. Menopause. 1999;6:7β13.
22.Wiseman H, Casey K, Bowey EA, Duffy R, Davies M, Rowland IR, LloydAS, Murray A, Thompson R, Clarke DB Influence of 10 wk of soy consumption on plasma concentrations and excretion of isoflavonoids and on gut microflora metabolism in healthy adults. Am J Clin Nutr, 80 (2004), pp. 692-699
23. Murkies AL, Lombard C, Strauss BJ, Wilcox G, Burger HG, Morton MS. Dietary flour supplementation decreases post-menopausal hot flushes: effect of soy and wheat. Maturitas, 21 (1995), pp. 189-195
24. Cancellieri F., De Leo V., Genazzani A.D., Nappi C., Parenti G.L., Polatti F., Ragni N., Savoca S., Teglio L., Finelli F., et al. Efficacy on menopausal neurovegetative symptoms and some plasma lipids blood levels of an herbal product containing isoflavones and other plant extracts. Maturitas. 2007;56:249β256.
25. Cheng G., Wilczek B., Warner M., Gustafsson J.-A., Landgren B.M. Isoflavone treatment for acute menopausal symptoms. Menopause. 2007;14:468β473.
26. Welty F.K., Lee K.S., Lew N.S., Nasca M., Zhou J.R. The association between soy nut consumption and decreased menopausal symptoms. J. Womens Health. 2007;16:361β369.
27. BolaΓ±os R, Del Castillo A, Francia J. Soy isoflavones versus placebo in the treatment of climacteric vasomotor symptoms: systematic review and meta-analysis. Menopause, 17 (2010), pp. 660-666
28. Newton KM, Grady D. Soy isoflavones for prevention of menopausal bone loss and vasomotor symptoms: comment on βSoy isoflavones in the prevention of menopausal bone loss and menopausal symptomsβ. Arch Intern Med, 171 (2011), pp. 1369-1370
29. Taku K, Melby MK, Kronenberg F, Kurzer MS, Messina M. Extracted or synthesized soybean isoflavones reduce menopausal hot flash frequency and severity: systematic review and meta-analysis of randomized controlled trials. Menopause, 19 (2012), pp. 776-790
30. Xu X, Harris KS, Wang HJ, Murphy PA, Hendrich S. Bioavailability of soybean isoflavones depends upon gut microflora in women. J Nutr, 125 (1995), pp. 2307-2315
31 Xu X, Wang HJ, Murphy PA, Cook L, Hendrich S. Daidzein is a more bioavailable soymilk isoflavone than is genistein in adult women. J Nutr, 124 (1994), pp. 825-832
32. Williamson-Hughes PS, Flickinger BD, Messina MJ, Empie MW. Isoflavone supplements containing predominantly genistein reduce hot flash symptoms: a critical review of published studies. Menopause, 13 (2006), pp. 831-839
33. St Germain A., Peterson C.T., Robinson J.G., Alekel D.L. Isoflavone-rich or isoflavone-poor soy protein does not reduce menopausal symptoms during 24 weeks of treatment. Menopause. 2001;8:17β26.
34. Tice J.A., Ettinger B., Ensrud K., Wallace R., Blackwell T., Cummings S.R. Phytoestrogen supplements for the treatment of hot flashes: The Isoflavone Clover Extract (ICE) Study: A randomized controlled trial. JAMA. 2003;290:207β214.
35. Hill D.A., Crider M., Hill S.R. Hormone therapy and other treatments for symptoms of menopause. Am. Fam. Physician. 2016;94:884β889.
36. Carmignani L.O., Pedro A.O., Costa-Paiva L.H., Pinto-Neto A.M. The effect of dietary soy supplementation compared to estrogen and placebo on menopausal symptoms: A randomized controlled trial. Maturitas. 2010;67:262β269.