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.
