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Soy Protein is Feminising? What do Studies say on the Effects of Soy and Men's Health?

Updated: Apr 16

soy protein feminising hormones

There have been locker room and social media stories about the feminising 'dangers' of soy for a few years now. From a muscle building perspective the latest evidence, including that from multiple randomised controlled human trials, shows that soy protein is beneficial for muscle building and recovery.

But is tofu, tempeh or soy protein powder a problem for men's hormones and health? Does soy give men 'man boobs' - moobs? Does soy feminise men? What do the studies say?

The science, across the growing body of literature, says No.

As ever, please talk to your doctor or medical practitioner most familiar with your medical history before implementing any changes in diet, exercise or lifestyle, especially if you are under treatment. Links to supporting studies and resources are found at the end of page.


The root of these 'feminising' facts comes primarily from data in the early 2000s. Some studies suggested there might be a link to testosterone disruption in men, although at that time the evidence from studies was mixed.

Creating the myth around soy was much a quoted 2008 case where a man who consumed almost 3 litres (3 quarts) of soy milk daily increased his oestrogen levels and developed gynecomastia.... moobs aka enlarged male breast tissue. The doctors wrote the case up , in their paper they concluded it was "a very unusual case of gynecomastia related to ingestion of soy products".

In 2020, in Japan, there was a similar case where the patient "described a daily intake of 3 quarts of soy milk. After he discontinued drinking soy milk, his breast tenderness resolved and his estradiol concentration slowly returned to normal."

Gynecomastia has multiple causes, including obesity and changes in testosterone during teenage years and after the age of 50, and as a side effect from medication.

In the area of hormonal health, most studies say there is no negative effect on male hormones. In some studies soy is shown to increase testosterone - the 'male' hormone. Soy is also shown to be beneficial in reducing men's risk of prostate cancer, a good reason to consume soy.

What about, say, sperm health? There have been mixed results from studies, including improvements in sperm quality from soy consumption. If you have concerns over this, then by all means reduce soy intake if and when you feel that you should. But you could benefit from enjoying soy! Want to keep your swimmers healthy? Rather than worrying about soy, avoid cigarettes, alcohol and diets high in processed foods. Concentrate on enjoying whole food patterns in keeping with a healthy Mediterranean diet as a 2020 Danish study demonstrated:

"dietary patterns favoring intakes of seafood, poultry, whole grains, legumes, skim milk, fruits, and vegetables have been consistently associated with better semen parameters in studies in North America, Europe, the Middle East, and Asia"

Are some people likely sensitive to soy? In rare instances yes. For the rest of us, enjoy soy as part of a balanced diet without worry. If you supplement in the gym, soy is a great option. As with all supplements, buy from a trusted, tested source.

To enjoy maximum health try to get as much variety in your diet, from as wide a range of food sources, as possible. And, of course, understand and prioritise self-care on your journey to health.

Stay Healthy,



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Related Studies

Zare R, Devrim-Lanpir A, Guazzotti S, Ali Redha A, Prokopidis K, Spadaccini D, Cannataro R, Cione E, Henselmans M, Aragon AA. Effect of Soy Protein Supplementation on Muscle Adaptations, Metabolic and Antioxidant Status, Hormonal Response, and Exercise Performance of Active Individuals and Athletes: A Systematic Review of Randomised Controlled Trials. Sports Med. 2023 Dec;53(12):2417-2446. doi: 10.1007/s40279-023-01899-w. Epub 2023 Aug 21. PMID: 37603200; PMCID: PMC10687132.

Monteyne AJ, Coelho MOC, Murton AJ, Abdelrahman DR, Blackwell JR, Koscien CP, Knapp KM, Fulford J, Finnigan TJA, Dirks ML, Stephens FB, Wall BT. Vegan and Omnivorous High Protein Diets Support Comparable Daily Myofibrillar Protein Synthesis Rates and Skeletal Muscle Hypertrophy in Young Adults. J Nutr. 2023 Jun;153(6):1680-1695. doi: 10.1016/j.tjnut.2023.02.023. Epub 2023 Feb 22. PMID: 36822394; PMCID: PMC10308267.

Nassan FL, Jensen TK, Priskorn L, Halldorsson TI, Chavarro JE, Jørgensen N. Association of Dietary Patterns With Testicular Function in Young Danish Men. JAMA Netw Open. 2020 Feb 5;3(2):e1921610. doi: 10.1001/jamanetworkopen.2019.21610. PMID: 32083688; PMCID: PMC7043196.

Povey AC, Clyma JA, McNamee R, Moore HD, Baillie H, Pacey AA, Cade JE, Cherry NM; Participating Centres of Chaps-UK. Phytoestrogen intake and other dietary risk factors for low motile sperm count and poor sperm morphology. Andrology. 2020 Nov;8(6):1805-1814. doi: 10.1111/andr.12858. Epub 2020 Jul 25. PMID: 32649041.

Haun CT, Mobley CB, Vann CG, Romero MA, Roberson PA, Mumford PW, Kephart WC, Healy JC, Patel RK, Osburn SC, Beck DT, Arnold RD, Nie B, Lockwood CM, Roberts MD. Soy protein supplementation is not androgenic or estrogenic in college-aged men when combined with resistance exercise training. Sci Rep. 2018 Jul 24;8(1):11151. doi: 10.1038/s41598-018-29591-4. Erratum in: Sci Rep. 2018 Aug 10;8(1):12221. PMID: 30042516; PMCID: PMC6057888.

Reed KE, Camargo J, Hamilton-Reeves J, Kurzer M, Messina M. Neither soy nor isoflavone intake affects male reproductive hormones: An expanded and updated meta-analysis of clinical studies. Reprod Toxicol. 2021 Mar;100:60-67. doi: 10.1016/j.reprotox.2020.12.019. Epub 2020 Dec 28. PMID: 33383165. (note: see Funding)

Applegate CC, Rowles JL, Ranard KM, Jeon S, Erdman JW. Soy Consumption and the Risk of Prostate Cancer: An Updated Systematic Review and Meta-Analysis. Nutrients. 2018 Jan 4;10(1):40. doi: 10.3390/nu10010040. PMID: 29300347; PMCID: PMC5793268.

Gynecomastia and Hypoganidism

Imai H, Nishikawa H, Suzuki A, Kodama E, Iida T, Mikura K, Hashizume M, Kigawa Y, Tadokoro R, Sugisawa C, Endo K, Iizaka T, Otsuka F, Nagasaka S. Secondary Hypogonadism due to Excessive Ingestion of Isoflavone in a Man. Intern Med. 2022 Oct 1;61(19):2899-2903. doi: 10.2169/internalmedicine.8578-21. Epub 2022 Feb 26. PMID: 35228414; PMCID: PMC9593161.

Sea JL, Abramyan M, Chiu HK. Prepubescent unilateral gynecomastia secondary to excessive soy consumption. J Pediatr Endocrinol Metab. 2020 Dec 14;34(4):521-525. doi: 10.1515/jpem-2020-0397. PMID: 33818045.

Martinez J, Lewi JE. An unusual case of gynecomastia associated with soy product consumption. Endocr Pract. 2008 May-Jun;14(4):415-8. doi: 10.4158/EP.14.4.415. PMID: 18558591.


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