10 Facts About Soy: health food or health hazard

By October 25, 2017Green Food

Soy foods Health food or harmful

Debunking myths around soy foods

There is a lot of controversy around whether soy is healthy versus harmful for you…So I thought I would clear a few things up with 10 evidence based facts about soy and soy foods.

I’ll be writing more detail about each of these topics in coming blog posts, so make sure you stay tuned!

Related articles:

What are soy foods?

Soybeans are a member of the pea (legume) family. Technically they are a vegetable, but due to their nutrition profile soy foods are often used as an alternative to meat and dairy.

Soy foods include tofu, tempeh, miso, soy beans/sprouts, soy nuts, natto, okara, soy milks/yoghurts, soy infant formula, edemame, TVP (textured vegetable protein), soy sauce and soy bean flours or oils,  as well as processed 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.

Since then things have been changing. Soy products  are now being marketed  in Australia as ‘healthy alternatives’ to milk and meat. Accordingly, national surveys show that younger Australians are more likely to consume soy foods than older adults. (4) Food analysts also estimate that consumption of soy and almond milk will have risen by 10% from 2010-2020. (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)!

Soy drink consumption graph | 10 facts about Soy - health food or health hazard?

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? And 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?

There are a few protective and health promoting compounds (phytonutrients) in soy foods, these are:

  • Isoflavones (flavanoids)
  • Phytosterols (plant sterols)
  • Saponins
  • Phytooestrogens

But how do these benefit or hinder health?

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.  (6-9)

Read my post about Soy and Hormones:Debunking the Myths

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 cancer. (10)

Typically, one serving (100g soy foods or 1 cup of soy milk) contains approximately 20-35mg of isoflavones.

Read my post about Does eating soy foods cause Cancer?

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. (11)

In a study, women who where 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. (12)

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.

100g of calcium set tofu contains:
Calcium 683g (68% RDI)
Protein 17g (27% RDI)
Omega 3 58mg (36% RDI)
Iron 3mg (33% RDI)
Selenium 17mg (25% RDI)
Magnesium 58mg (15% RDI)
Zinc 2mg (11% RDI)
Fibre 2mg (8% RDI)

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 soy bean. 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 the development of breast, prostate, lung, and colon cancer. (13)

These issues are not true for whole soy products e.g. edemame, miso, soy beans, tofu, tempeh, soy milks. For this reason I do not recommend people eat products with soy protein isolate, including heavily processed ‘mock meats’ or 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.(14) 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 of 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 can not 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. (15-16) 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 away 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 my blog post, Can vegans get enough protein?’ for more information.

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. (17) Soy isoflavones are also a powerful antioxidant that help reduce LDL cholesterol oxidation(18). LDL is a bad 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 (3-4 serves) eaten daily has been shown to lower LDL cholesterol and reduce the risk of developing heart disease! (19-21)

So there you have it! Ten facts about soy foods showing that whole soy foods (including tofu, tempeh, miso, soy beans, natto, soy milk, soy infant formula, edemame 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 soy beans and soy protein isolate should be avoided. Also anyone on thyroid medications should consult their GP and dietitian about their soy food intake.

Want more information about soy? Well, stay tuned because I will be going into each of these facts in depth, explaining the science. Sign-up to the newsletter to receive updates straight to your inbox when new posts pop up.

If you want to find out easy and versatile ways to add more soy foods into your diet you can book a consultation with me for recommendations personalised to your needs!

Related articles:

Nutrition post written by plant-based dietitian (APD) Amber Sewell-Green

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(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)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.

(7) Habito, R. C.Montalto, J.Leslie, E. & Ball, M. J.(2000Effects of replacing meat with soyabean in the diet on sex hormone concentrations in healthy adult malesBritish Journal of Nutrition 84557563.

(8) Nagata, C.Takatsuka, N.Shimizu, H.Hayashi, H.Akamatsu, T. & Murase, K.(2001Effect of soymilk consumption on serum estrogen and androgen concentrations in japanese menCancer Epidemiology, Biomarkers and Prevention 10179184.

(9)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

(10) 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.

(11) 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.

(12) S M PotterJ A BaumH 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.

(13) 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.

(14) 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

(15) 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.

(16) 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.

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

(18) Wiseman HO’Reilly JDAdlercreutz 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

(19) 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.

(20) 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 

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

Amber Sewell-Green

Author Amber Sewell-Green

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