10 Facts About Soy: Health Food or Health Risk?

There is a lot of controversy around whether soy is healthy versus harmful for you.

We know that some are concerned about the safety of soy-rich diets. For instance, some people worry that eating too much soy could increase their chance of developing breast cancer, interfere with their thyroid's ability to function, or make them more feminine.

We’ve put together this article to help you determine whether eating soy has a positive or negative effect on your health and bust some myths using scientific research.

First up – what are soy foods?

Soybeans are a member of the pea (legume) family.

Technically they are a vegetable, but due to their nutrition profile and higher protein, calcium and energy content soy foods are often used as an alternative to meat and dairy.

Soy foods include:

-       Tofu

-       Tempeh

-       Miso

-       Edamame

-       Soy beans/sprouts

-       Soy nuts

-       Natto

-       TVP (textured vegetable protein)

-       Okara

-       Soy milks and yoghurts

-       Soy infant formula

-       Soy sauce and soybean flours or oil

-       Soy protein isolate found in some mock meats and protein powders or bars.

How much soy foods do Australians consume?

Soy foods are a staple in traditional Asian diets. Japanese people have the highest intakes, eating around 65g of soy per person each day, mostly as tofu and miso (1).

Japan and other Asian soy-consuming countries typically have lower rates of heart disease and certain cancers (2-3). This has led scientists to believe that soy foods could be beneficial for health.

However, Australians typically consume much less! In fact, in 2012 less than 2% of Australians’ diets contained soy foods and less than half of Australian women would eat 1 serve (100g) of soy foods daily.

But, since then, things have been changing rapidly! Soy products are now being marketed in Australia as ‘healthy alternatives and even “better options” to milk and meat.

Accordingly, national surveys show that younger Australians are more likely to consume soy foods than older adults, but even this is changing now (4).

Food analysts estimated that consumption of soy and almond milk would rise by 10% from 2010-2020 and they were right! (5) Soy drinks are also now the most popular drink for Australians, above energy drinks, sport drinks, iced teas and even breakfast drinks (i.e., juice)!

In fact, due to the rapid interest in meat substitutes in the last decade, the average Australian’s now consumes 16% more soy milk and almost 30% more meat alternatives since 2019, at up to 20g/day of soy per person per day for some individuals (6)

Source: Roy Morgan Single Source (Australia), April 2011-March 2012 (n=19,690) and April 2015-March 2016 (n=15,074).

So, is this a good or a bad thing? Are the health benefits of soy foods seen in Asians also applicable for Western societies such as us Aussies?

What part of soy foods promote health?

Aside from being rich in iron, calcium and protein, there are a few protective and health promoting compounds (phytonutrients) that are unique to soy foods. These are:

·         Isoflavones (flavonoids)

·         Phytosterols (plant sterols)

·         Saponins

·         Phytoestrogens

But do these benefit or hinder health? Lets take a look…

10 Facts About Soy Foods:

Fact 1: Soy foods do not cause breast or ‘manboob’ growth

The oestrogen like compounds (isoflavones) in soy foods do not attach to oestrogen receptors in the chest (breast and pectoral) or genital tissue. There are currently NO studies showing that soy isoflavones affect our hormone system. This means that (whole) soy foods do not cause the growth of bigger breasts in women or ‘man-boobs’ in men. They are also not linked with lactation in men. (7-10)

However, soy foods can be high in energy, and as with any food if you consume wayyy more energy that what your body needs you may start storing this as extra cushin for the pushin. So as always, aim to eat based on your unique appetite cues.

Fact 2: Soy foods could help protect against cancer

Because soy isoflavones do not stimulate cell growth in most regions of the body, soy foods do not cause cancer growth. In fact, isoflavones may even protect against cancers. Recent studies suggest that higher intakes of soy decreased cancer risk by 10% and that every additional 10-25g/day consumed reduces risk of all cancers, but in particular bowel, gastric, breast, prostate, endometrial and even lung cancer by 4-50%, so an extra 50g-100g/day is an 8-16% reduced risk and so forth (11-13)

Typically, one serving (100g soy foods or 1 cup of soy milk) contains approximately 20-35mg of isoflavones. However, generally around 30-50mg daily in linked to health benefits such as cancer prevention.

Examples of the average isoflavone content of some foods include:

1.      half a cup of soybeans – 40 to 75mg isoflavones

2.      quarter cup of soy flour – 45 to 69mg isoflavones

3.      one 250ml glass of soy drink – 15 to 60mg isoflavones

4.      one 115g block of tofu – 13 to 43mg isoflavones

5.      one 110g block of tempeh – 41mg isoflavones

6.      one container of soy yoghurt – 26mg isoflavones

7.      2 slices of soy bread – 7 to 15mg isoflavones

8.      One teaspoon of soy sauce – 0.4 to 2.2mg isoflavones.

Fact 3: Soy foods help create strong bones and protect against osteoporosis

The isoflavones in soy foods DO attach to receptors in your bones to create new bone and reduce bone loss. Asians consuming higher amounts of soy have lower risk of bone fractures, especially hip fractures. (14)

In a study, women who were fed 40g of soy protein daily (90mg isoflavones) had a significantly higher bone mineral density (better bones) compared to the women who were fed less isoflavones (56mg) or casein (cow) protein. (15)

Fact 4: Soy foods are an excellent source of vitamins and minerals

Soy foods are rich in calcium, iron, zinc, omega 3, selenium, magnesium, fibre and protein. They are also typically lower in fat (including saturated fat and cholesterol) and sodium than their animal-based alternatives.

RDIs are for an adult male aged 19-70 years old, with high nutrient needs

Fact 5: Soy protein isolate does have some links with cancer and is stripped of nutrients and fibre

Soy protein isolate is found in protein powders and some processed foods e.g., mock meats. It is the soy protein extracted (isolated) from the soybean. This process leaves behind the good stuff like fibre and other nutrients. There is some evidence linking soy protein isolate with cancer.  Studies show isolated soy protein increases IGF-1 factor more than dairy. Increased IGF-1 has been strongly LINKED TO CONTRIBUTE TO breast, prostate, lung, and colon cancer. (16)

These issues are not true for whole soy products e.g. edamame, miso, soy beans, tofu, tempeh, soy milks. For this reason, we do not recommend people eat products with soy protein isolate, including heavily processed ‘mock meats’ or whole bean based soy-based protein powders.

Fact 6: Soy formulas are safe and viable to feed to infants

A longitudinal study of almost 250 adults (aged 20-34years) who were fed soy formula as infants found that the formula had no effect on their fertility, maturation, rates of miscarriage or birth defects in their offspring. (17) Basically they grew up into normal healthy adults.

Fact 7: GMO soy foods can be harmful to health

GM (genetically modified) soybeans are resistant to pesticides and herbicides. This is so that farmers can spray a field and kill all the weeds and pests without killing their crops. The result is that the soybeans are heavily coated with pesticides and herbicides too. The safety of this cannot be confirmed. Experts estimate 80% of global soy and corn crops at genetically modified. Check the ingredients list to confirm this (look out for non-GMO or organic soy or soybeans - this is what you want!). 

Fact 8: Soy foods could reduce the effects of thyroid medications

Soy has been shown to reduce the effects of thyroid medications. (18-19) This does not mean you have to totally avoid soy foods. It is best to consult your GP or dietitian about your soy threshold and also to take thyroid meds at separate times from meals.

Fact 9: Soy foods are a ‘complete protein’ and contain all nine essential amino acids our body needs

Amino acids are the building blocks of protein. See our blog post, ‘Can vegans get enough protein?’ for more information on this topic.

There are 20 amino acids that our body uses to make protein. Nine of these amino acids are ‘essential’, meaning that our body cannot make them itself and needs to get them from food. If a food contains all nine essential amino acids is it considered a ‘complete protein’. Animal products are complete proteins.

Alternatively, most plants contain many, but not all, of the amino acids, making them ‘incomplete proteins’.

However, there are a few plant foods, such as soy, that contain ALL nine amino acids, making them a complete protein, comparable to animal products.

Facts 10: Soy protein in foods can reduce your cholesterol levels and chance of having a heart attack

The saponins and phytosterols in soy foods help remove cholesterol from the body. (20) Soy isoflavones are also a powerful antioxidant that help reduce LDL cholesterol oxidation (21). LDL is what I call the  ‘lousy’ type of cholesterol (think ‘L’ for lousy) and LDL oxidation is a key step that leads to having a heart attack or stroke.

According to the USDA, just 25g of soy protein (1-3 serves) eaten daily has been shown to lower LDL cholesterol and reduce the risk of developing heart disease! (22-23). But remember, every little bit counts, especially if soy foods are replacing other foods which may be increasing your cholesterol levels!

In Summary

There you have ten facts about soy foods showing that whole soy foods (including tofu, tempeh, miso, soy beans, natto, soy milk, soy infant formula, edamame and TVP) contribute health benefits, help protect against chronic lifestyle based diseases and are an important part of a healthy diet. Soy foods have proven health benefits and a good source of nutrition, especially for vegans and vegetarians.

However, foods with GMO soybeans and  soy protein isolate  are why soy gets a such a bad rep, and should be avoided where possible. Also, anyone on thyroid medications should consult their GP and dietitian about their soy food intake.

If you want to find out easy and versatile ways to add more soy foods into your diet, you can book a consultation us at The Green Mind for recommendations personalised to your needs. If you would like to join our appointment waiting list, please drop us an email at: hello@thegreenmind.com.au

References

(1) Nagata C. Ecological study of the association between soy product intake and mortality from cancer and heart disease in Japan. Int J Epidemiol. 2000;29:832-836.

(2) Ferlay J, Soerjomataram I, Dikshit R et al. Cancer incidence and mortality worldwide: Sources, methods and major patterns in GLOBOCAN 2012. International Journal of Cancer. 2014;136(5):E359-E386.

(3) Hanna L, O’Neill S, & Wall L. (2010). Intake of isoflavone and lignan phytoestrogens and associated demographic and lifestyle factors in older Australian women. Asia Pacific Journal of Clinical Nutrition, 19(4), 540-549. 

(4) National Nutrition and Physical Activity Survey, 2011-12.

(5)  IBISWorld Industry Report OD5256: Soy and Almond Milk Production in AustraliaMarket Research Reports & Analysis. IBISWorld AU. 2017 [cited 23 October 2017]. Available from: http://clients1.ibisworld.com.au/reports/au/industry/default.aspx?entid=5256

(6) Australian Bureau of Statistics. (2020-21). Apparent Consumption of Selected Foodstuffs, Australia. ABS. https://www.abs.gov.au/statistics/health/health-conditions-and-risks/apparent-consumption-selected-foodstuffs-australia/2020-21.

(7)Morito K, Hirose T, Kinjo J et al (2001). Interaction of Phytoestrogens with Estrogen Receptors .ALPHA. and .BETA.. 2001. Biological and Pharmaceutical Bulletin, 24;4: 351-356.

(8) Habito, R. C., Montalto, J., Leslie, E. & Ball, M. J.(2000) Effects of replacing meat with soyabean in the diet on sex hormone concentrations in healthy adult males. British Journal of Nutrition 84, 557–563.

(9) Nagata, C., Takatsuka, N., Shimizu, H., Hayashi, H., Akamatsu, T. & Murase, K.(2001) Effect of soymilk consumption on serum estrogen and androgen concentrations in japanese men. Cancer Epidemiology, Biomarkers and Prevention 10, 179–184.

(10)NTP-CERHR Monograph on soy infant formula No. 10-5995 [Internet]. National Toxicology Program: Center for the Evaluation of Risks to Human Reproduction; 2010 [cited 23 October 2017]. Available from: https://ntp.niehs.nih.gov/ntp/ohat/genistein-soy/soyformula/soymonograph2010_508.pdf

(11) Yamamoto S, Sobue T, Kobayashi M, Sasaki S, Tsugane S. Soy, Isoflavones, and Breast Cancer Risk in Japan. JNCI Journal of the National Cancer Institute. 2003;95(12):906-913.

(12) Fan, Y., Wang, M., Li, Z., Jiang, H., Shi, J., Shi, X., Liu, S., Zhao, J., Kong, L., Zhang, W., & Ma, L. (2022). Intake of Soy, Soy Isoflavones and Soy Protein and Risk of Cancer Incidence and Mortality. Frontiers in Nutrition (Lausanne), 9, 847421–847421. https://doi.org/10.3389/fnut.2022.847421

(13) Nachvak, S. M., Moradi, S., Anjom-shoae, J., Rahmani, J., Nasiri, M., Maleki, V., & Sadeghi, O. (2019). Soy, Soy Isoflavones, and Protein Intake in Relation to Mortality from All Causes, Cancers, and Cardiovascular Diseases: A Systematic Review and Dose–Response Meta-Analysis of Prospective Cohort Studies. Journal of the Academy of Nutrition and Dietetics, 119(9), 1483–1500.e17. https://doi.org/10.1016/j.jand.2019.04.011

(14) Ross P, Norimatsu H, Davis J, Yano K, Wasnich R, Fujiwara S et al. A Comparison of Hip Fracture Incidence among Native Japanese, Japanese Americans, and American Caucasians. American Journal of Epidemiology. 1991;133(8):801-809.

(15) S M Potter, J A Baum, H Teng et al.Soy protein and isoflavones: their effects on blood lipids and bone density in postmenopausal women. Am J Clin Nutr. 2000;72:844-852.

(16) Yu H. Role of the insulin-like growth factor family in cancer development and progression. J Natl Cancer Inst. 2000 Sep 20;92(18):1472-89.

(17) Alexander D, Ball MJ, Mann J. Nutrient intake and haematological status of vegetarians and age matched omnivores. Eur J Clin Nutr. 1994;48:538-546

(18) Sathyapalan T, Manuchehri A, Thatcher N, Rigby A, Chapman T, Kilpatrick E et al. The Effect of Soy Phytoestrogen Supplementation on Thyroid Status and Cardiovascular Risk Markers in Patients with Subclinical Hypothyroidism: A Randomized, Double-Blind, Crossover Study. The Journal of Clinical Endocrinology & Metabolism. 2011;96(5):1442-1449.

(19) Jabbar M, Larrea J, Shaw R. Abnormal thyroid function tests in infants with congenital hypothyroidism: the influence of soy-based formula. Journal of the American College of Nutrition. 1997;16(3):280-282.

(20) Mahan L, Escott-Stump S. Krause’s food, nutrition, & diet therapy. Philadelphia: Saunders; 2004.

(21) Wiseman H, O’Reilly JD, Adlercreutz H, et al. Isoflavone phytoestrogens consumed in soy decrease F(2) isoprostane concentrations and increase resistance of low-density lipoprotein to oxidation in humans. Am J Clin Nutr. 2000;72(2):395-400

(22) Taku K, Umegaki K, Sato Y et al. 2007, ‘Soy isoflavones lower serum total and LDL cholesterol in humans: a meta-analysis of 11 randomized controlled trials’, American Journal of Clinical Nutrition, vol. 85, no. 4, pp. 1148–1156.

(23) Reynolds K, Chin A, Lees K et al. 2006, ‘A meta-analysis of the effect of soy protein supplementation on serum lipids’, The American Journal of Cardiology, vol. 98, no. 5, pp. 633–640. More information 

(24) Frank M et al. 2006, ‘Soy Protein, Isoflavones, and Cardiovascular Health’, Arteriosclerosis, Thrombosis, and Vascular Biology, vol. 26, pp. 1689-1692. More information here.