Soy Consumption: Addressing Common Concerns

Written by Madeline Blackburn

What is Soya?

Soya, or soy, is a derivative of the soybean, a legume most widely consumed in East Asian cuisine, though is becoming increasingly popular in Western countries too (1). The soybean sector has a current global market value of over $150 billion (2). The rising popularity of soya is influenced by its versatility, in conjunction with a growing interest in plant-based diets as well as an alternative to dairy products. 

Soya products include soya milk, tofu, edamame, tempeh, miso and soy sauce. It is also contained in many products that are not soya based, in fact approximately 60% of manufactured pre-packaged foods contain soya, because it is versatile and can be used as a protein filler, emulsifier or texturiser (3). However, there are some concerns surrounding soya products that are making some people hesitant to consume it.

What are these concerns, and are they worth considering?

Soya and Hormones 

There are two main concerns that surround soya and hormones. These concerns have arisen because soy contains isoflavones which are a form of phytoestrogen- or plant-oestrogen. The first concern is that soya could affect fertility. In terms of female fertility, there are some clinical trials that show that frequently consuming large quantities of soya may increase the length of the menstrual cycle (4), but these studies are limited. Overall, there is no clear evidence to suggest that soya should have significant negative effects in healthy women’s fertility when consumed in moderation (4). With regards to men’s hormones, there are concerns that consuming phytoestrogens could have a feminising effect. But there is no evidence to suggest that this should be true, with no significant effect of consuming soya on oestrogen or testosterone levels (5). 

Soya and Cancer

Some people are concerned over whether soya may increase the risks of certain cancers such as breast cancer, once again, due to soya containing phytoestrogens. Increased levels of oestrogen have been linked to an increased risk of breast cancer (6). However, plant-based oestrogens are not exactly the same as human oestrogen (7) and have a much milder effect when consumed (8). Therefore, a moderate amount of soya is not shown to increase your risk of breast cancer (9). In fact, some evidence suggests that eating soya throughout your life, beginning when you are a child, could have a protective effect against breast cancer (9).  

Soya and Thyroid 

The thyroid gland is important for growth, development and metabolism (10). There is some speculation that soya may affect its function by inhibiting some of the hormone secretion. Whilst the phytoestrogens can bind to oestrogen receptors and therefore impact the hormone, their effect is seen to be clinically insignificant for individuals with normal thyroid functionality (11). For those with thyroid related conditions such as goitre or hypothyroidism, the impact could be more noticeable (11), especially if taking related medication as soya may affect the absorption (12). If in doubt it would be sensible to speak to a health professional about this. 

Soya and Digestion

Hesitation surrounding soya is also influenced by the idea that it is not easily digested in humans. Soya is generally digested further down the gastrointestinal tract in the colon rather than the small intestine (9). This is because soya contains a type of carbohydrate form known as oligosaccharides which cannot be digested well by the intestinal enzymes (9). This may cause bloating or flatulence which may make people believe that the soya is being poorly digested, however by being digested in the colon, it is contributing to Bifidobacteria levels in your gut microbiome which is considered to be beneficial to your health (9). Notably, soya is one of the 14 major allergens, so if you are concerned about your reaction, it may be best to get it checked out (3). 

Despite these concerns, there are also some well-researched benefits of including soya in your diet. 

Soya and the Menopause

One of the most well-studied areas when it comes to soya is its beneficial effects for menopausal women. As already mentioned, soya contains isoflavones which are plant-oestrogens. Whilst they are not exactly the same as human oestrogens, they are able to bind to oestrogen receptors in the body giving a simulation of the human oestrogen response (13). This has proven to be useful in the alleviation of some of the side effects of the menopause, such as hot flushes (12;14). Whilst including soya in your diet is no substitute for clinical intervention such as HRT (12), its benefits are still notable. Soya is also shown to aid bone health during menopause which is important as it is a time where bone density decreases and puts women at higher risk of osteoporosis (15). One study also demonstrates the benefits isoflavones have for skin health in postmenopausal women, aiding hydration, wrinkles and dyspigmentation (16). The benefits for menopause symptom relief via soya is often found to be most prevalent alongside a plant-based diet (17).

Soya in Plant-Based Diets

Soya is utilised by many as it is high in protein and this protein is also of a high quality (9). This means a large amount of the protein can be digested (9). This could be a good alternative source of protein especially for individuals who follow a more plant-based diet. Plant-based diets are shown to have an array of health benefits such as positive effects on blood pressure and cholesterol levels as well as generally being more cost-effective (18). Soya-based meat substitutes are often highly processed and therefore it is suggested that more traditional soya foods such as tofu, tempeh and soya milk would be a slightly better way of incorporating it into your diet (18). Not only is soya a source of protein, but it is also a source of micronutrients, such as iron, and products like soya milk can be fortified with calcium and vitamin D too (18). 

Should we incorporate soy into our diets? 

There are several concerns that surround the consumption of soya products. News headlines and social media make it difficult to obtain well-rounded facts about nutrition, meaning that ideas get blown out of proportion- an example being soya’s effect on the thyroid gland- it could seem like soya could have a negative impact because it can do for individuals with pre-existing thyroid conditions, but for most people, it is unlikely to have a significant effect. However, overall, there is no conclusive evidence to suggest that we should stop consuming soya, and in fact, there could be plenty of benefits from doing so. 

As with all foods, there are a few things to bear in mind when consuming soya. Firstly, consume it in moderation. No diet should be focussed solely around one food type. Secondly, the effects of soya will vary from person to person for various physiological reasons such as age, sex, and ethnicity, as well as the level of exposure to the phytoestrogens (19); some people may see effects such as fewer hot flushes, when someone else may not. But perhaps if you don’t currently consume soya products like tofu, tempeh and soya milk, they might be worth incorporating due to the evidenced benefits. 

References:

1) Rizzo, G. and Baroni, L. (2018) ‘Soy, soy foods and their role in vegetarian diets’, Nutrients, 10(1). Available at: https://doi.org/10.3390%2Fnu10010043 (Accessed: 22 April 2024)

2) IISD (2024) Soybean prices and sustainability. Available at: https://www.iisd.org/system/files/2024-02/2024-global-market-report-soybean.pdf (Accessed: 27 April 2024)

3) Allergy UK (2021) Soya allergy. Available at: https://www.allergyuk.org/resources/soya-allergy-factsheet/ (Accessed: 27 April 2024)

4) Rizzo, G., Feraco, A., Storz, M., Lombardo, M. (2022) ‘The role of soy and soy isoflavones on women’s fertility and related outcomes: an update’, Journal of nutritional science, 11, 17. Available at: https://doi.org/10.1017%2Fjns.2022.15 (Accessed: 29 April 2024)

5) Reed, K., Camargo, J., Hamilton-Reeves, J., Kurzer, M., Messina, M. (2021) ‘Neither soy nor isoflavone intake affects male reproductive hormones: an expanded and updated meta-analysis of clinic studies’, Reproductive toxicology, 100, 60-67. Available at: https://doi.org/10.1016/j.reprotox.2020.12.019 (Accessed: 14 April 2024)

6) NHS (2024) Causes of breast cancer in women. Available at: https://www.nhs.uk/conditions/breast-cancer-in-women/causes-of-breast-cancer-in-women/ (Accessed: 29 April 2024)

7) Lambert, R. (2021) The science of nutrition. Great Britain: Dorling Kindersley Limited. 

8) Cancer Research (2022) Food myths and cancer. Available at: https://www.cancerresearchuk.org/about-cancer/causes-of-cancer/diet-and-cancer/food-controversies (Accessed: 5 May 2024)

9) Messina, M. (2016) ‘Impact of soy foods on the development of breast cancer and the prognosis of breast cancer patients’, Research in complementary medicine, 23(2), 75-80. Available at: https://doi.org/10.1159/000444735 (Accessed: 29 April 2024)

10) Armstrong, M., Asuka, E., Fingeret, A. (2023) ‘Physiology, thyroid function’ in StatPearls, Treasure Island: StatPearls publishing. Available at: https://www.ncbi.nlm.nih.gov/books/NBK537039/ (Accessed: 29 April 2024)

11) Otun, J., Sahebkar, A., Östlundh, L., Atkin, S., Sathyapalan, T. (2019) ‘Systematic review and meta-analysis on the effect of soy on thyroid function’, Scientific reports, 9, 3964. Available at: https://doi.org/10.1038%2Fs41598-019-40647-x (Accessed: 30 April 2024)

12) BDA (2022) Soya foods and your health. Available at: https://www.bda.uk.com/resource/soya-foods.html (Accessed: 14 April 2024)

13) Desmawati, D. and Sulastri, D. (2019) ‘Phytoestrogens and their health effect’, Open access Macedonian journal of medical sciences, 7(3), 495-499. Available at: https://doi.org/10.3889%2Foamjms.2019.086 (Accessed: 5 May 2024)

14) Dastjerdi, M., Eslami, B., Sharifi, M., Moini, A., Bayani, L., Khani, H., Alipour, S. (2018) ‘Effect of soy isoflavone on hot flushes, endometrial thickness, and breast clinical as well as sonographic features’, Iranian journal of public health, 47(3), 382-389. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5971175/ (Accessed: 2 May 2024)

15) Barańska, A., Kanadys, W., Bogdan, M., Stępień, E., Barczyński, B., Kłak, A., Augustynowicz, A., Szajnik, M., Religioni, U. (2022) ‘The role of isoflavones in the prevention of bone loss in postmenopausal women: a systematic review with meta-analysis of randomised controlled trials’, Journal of clinical medicine, 11(16), 4676. Available at: https://doi.org/10.3390%2Fjcm11164676 (Accessed: 2 May 2024)

16) Rizzo, J., Min, M., Adnan, S., Afzal, N., Maloh, J., Chambers, C., Fam, V., Sivamani, R. (2023) ‘Soy Protein Containing Isoflavones Improves Facial Signs of Photoaging and Skin Hydration in Postmenopausal Women: Results of a Prospective Randomized Double-Blind Controlled Trial’, Nutrients, 15(19), 4113. Available at: https://doi.org/10.3390/nu15194113 (Accessed: 14 April 2024)

17) Barnard, N., Kahleova, H., Holtz, D., Del Aguila, F., Neola, M., Crosby, L., Holubkov, R. (2021) ‘The Women's Study for the Alleviation of Vasomotor Symptoms (WAVS): a randomized, controlled trial of a plant-based diet and whole soybeans for postmenopausal women’, The journal of the menopause society, 28(10), 1150-1156. Available at: https://doi.org/10.1097/GME.0000000000001812 (Accessed: 2 May 2024)

18) Tuso, P., Ismail, M., Ha, B., Bartolotto, C. (2013) ‘Nutritional update for physicians: plant-based diets’, The permanente journal, 17(2). Available at: https://doi.org/10.7812/TPP/12-085 (Accessed: 4 May 2024)

19) Domínguez-López, I., Yago-Aragón, M., Salas-Huetos, A., Tresserra-Rimbau, A., Hurtardo-Barroso, S. (2020) ‘Effects of dietary phytoestrogens on hormones throughout a human lifespan: a review’, Nutrients, 12(8), 2456. Available at: https://doi.org/10.3390%2Fnu12082456 (Accessed: 2 May 2024)