The Stance on SOY: What Does The Research Say?

There is great debate on its health impacts, so let’s dive into the science of soy. 

It can be incredibly confusing to navigate through the numerous good, and bad claims about soy consumption. Soybeans are a type of legume and can be found as: 

  • Whole food sources (most commonly edamame beans) 
  • Fermented sources (soy sauce, natto and miso) 
  • Processed foods (e.g. yoghurt, cheese, bread, breakfast cereals and meat alternatives – tofu, tempeh, TVP). 

Isoflavones and Oestrogen: 

When it comes to soy, the components of most debate are the isoflavones, which are polyphenols with oestrogen properties – meaning the isoflavone chemical structure is likened to oestrogen (a hormone). 

Many people will avoid soy due to the fact that soy, or soy products will act like the hormone oestrogen in our bodies – so to what extent is this true? 

Since isoflavones and oestrogen have a similar chemical structure, isoflavones can bind to oestrogen receptors in the body, causing a weak, anti-oestrogenic, (prevent oestrogen from mediating any effect), or NIL effect. It is important to note that the human body contains a number of different oestrogen receptors, and isoflavones do not bind to ALL of those receptors. Therefore, phytoestrogens will not reflect the typical agonist response of classical oestrogens. 

Picture source: https://www.superfoodly.com/estrogen-foods-list-50-high-phytoestrogen-sources/ 

Reference:  G, Rizzo & L, Baroni, 2018, ‘Soy, Soy Foods and Their Role in Vegetarian Diets’, The Science of Vegetarian Nutrition and Health, 10(1), Accessed from: https://www.mdpi.com/2072-6643/10/1/43/htm 

Soy and our Health: 

As the science currently stands, the following points are evidence-based facts on the consumption of soy products. 

  • Complete source of plant-based protein (i.e. contains all 9 essential amino acids) 
  • Source of unsaturated fatty acids; has exerted positive effects towards cholesterol status.  
  • May reduce LDL cholesterol for those with high cholesterol status. 
  • May reduce risk of coronary heart disease 
  • Soy will not affect testosterone levels in men 
  • Source of B vitamins 
  • High in fibre (1 cup cooked soybeans = 14g fibre) 
  • The type of carbohydrates in soy are indigestible to humans, so they are fermented in the large intestine to feed and grow our gut microbiota 
  • May be protective against development of breast, prostate and bowel cancer 
  • Contains phytic acid – which affects the absorption of some minerals such as calcium and iron. By cooking or fermenting soy, it deactivates the phytic acid. 
  • Unlikely effects to overall thyroid function. However, it is suggested for those on levothyroxine, to distance soy consumption from medication intakes due to potential interference/interactions. 

So, to summarise: 

Soy is not AS BAD as the claims set it out to be. As with all foods, try to avoid consuming excessive amounts of soy. 25g of soy per day is the recommended amount – which is equivalent to around 100g of tofu, tempeh, or soybeans. 

Tahlia Claringbold

Based in Sydney, Australia, I have recently graduated as a Nutritionist from the University of Wollongong, completing my Bachelor of Nutrition Science (BNutSci) in 2019.

I am now completing my Master of Nutrition and Dietetics (also at UOW) to graduate as an Accredited Practicing Dietitian (APD) in 2021.

I am a passionate foodie who loves to cook, bake, learn and educate others.

My favourite foods include sushi, chocolate and avocado. I love cats, yoga, baking, and my friends. I have particular interests in digestive health, adolescent nutrition and women’s nutrition.

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