Author: Nina Gabriela, Nutritionist
Should soy be avoided? Is it a wreaking havoc for our health, or is it good for us? What about the hormones? There seems to be a never-ending debate about soy, with varying opinions on whether it’s good or bad for you. So is soy to be avoided, or is soy healthy? Plant-based Nutritionist, Nina Gabriela, guides us with some tips when considering the research behind soy.
To be honest, there is a lot of conflicting information, views and opinions out there on soy. It can be incredibly confusing and tricky to decipher fact from fiction, even in the world of scientific studies. The problem is exactly that: Most of what you read about soy are opinions. Not science, and not facts. I’m going to start with the basics, by defining what soy actually is.
Soy is a type of legume, or in other words, a bean. In its whole form, soy is a soybean. You might be familiar with edamame beans, which are young green soybeans. From the mature soybeans, a whole variety of different products are created. Minimally processed, wholesome soy-based products include the popular tofu, tempeh and soy milk. Soy can also be transformed into almost unrecognisable form to make products such as soy protein isolate, soy lecithin and other soy extracts. These are common ingredients in vegan meats, candy bars and protein bars.
When reading the conclusions drawn from research studies, it is important to acknowledge that they often focus on one particular part of soy and the potential health risks or benefits, as opposed to viewing soy as a whole food, which is how we often consume it. For example, the compounds most commonly studied are isoflavones, a form of phytoestrogen (plant oestrogen). Yet isoflavones are not eaten in isolation. Whole, intact food with many other nutrients and compounds, all working together synergistically act very differently in the body to a refined and isolated nutrient compound.
Another important thing to note is that most studies are done in vitro (meaning, in a test tube) or in animals (who actually metabolise soy very differently to us!), so we cannot assume with great accuracy that the same processes will occur inside the human body. Other studies look at the effects of eating over 14-15 servings of soy per day, which is typically not consumed in a balanced, plant-based diet.
When interpreting research findings, it is always beneficial to be aware of the funding body who has supported the research to reveal potential biases. This is because there is a well-known publication bias in scientific research, meaning that if results do not turn out in favour of the hypothesis, they are unlikely to be published. An example of detecting potential biases is to have awareness if a study supportive of soy is funded by the soy industry, or alternative, if a study against soy is supported by the meat or dairy industry.
First, let’s explore the myth about oestrogen-like properties. The compound I mentioned earlier, isoflavones, do in fact have a very similar chemical structure to the oestrogen hormone found in our own bodies. This allows isoflavones to bind to our oestrogen receptors – but does it truly ACT like oestrogen in the human body?
Well, as it turns out, there are actually different oestrogen receptors in the human body, and isoflavones don’t bind to all of them (the ones they bind to are called transactivates ER-beta, but you don’t really need to know this). As they selectively bind to receptors that are different from the ones that our own oestrogen hormone binds to, they have very different effects in the body. Sometimes the exact opposite effects to oestrogen (as well as being 1000 times weaker than actual oestrogen).
Isoflavones block some of oestrogen’s effects, and mimic others, which has generally been associated with health benefits. Isoflavones also have antioxidant and anti-inflammatory properties. Oh, and another fun fact, these phytoestrogens are also found in chickpeas and flaxseeds, among other plant foods, yet have you heard anyone demonising these?
Studies show that soy may actually reduce the risk of oestrogen-dominant conditions, such as endometriosis, menopause symptoms and breast cancer. Some of the lowest breast cancer rates in the world are in Asian countries, where the most soy is consumed. Contrary to the popular myth, soy does not cause ‘man boobs’. However, the mammalian oestrogen that is found in animal products, such as dairy, which, unlike soy oestrogen’s, does have the same effects in our bodies as our own oestrogen hormone.
The majority of GMO soy is very highly sprayed with herbicides and pesticides and is fed to chickens, cattle and pigs, which are then also consumed by people. To this end, organic is always better. Now that’s a lot to consider, and you might be feeling even more confused. To avoid further worry, I have put together a summary of the research for you. I am basing these conclusions on soy only on the evidence that I feel is relevant, reliable and translatable to humans.
Let’s get to what the evidence says on soy:
- Soy is a great source of plant-based protein and contains all the essential amino acids, making it a ‘complete’ protein.
- Soy is high in fibre, and a rich source of prebiotics. This helps feed the good bacteria in the gut to promote a healthy microbiome and digestive system.
- Soy has been shown to improve bone density and protect against osteoporosis and fractures.
- Soy appears to have no effect on the thyroid, as long as you are meeting your iodine needs (which is essential whether or not you eat soy!). However, it may reduce levothyroxine absorption (this is a drug often taken by people with hypothyroidism), therefore it is advised that people taking this medication avoid high doses of soy protein, such as soy protein powders, as well as not eat soy foods within 2-4 hours of taking their medication.
- Phytic acid is found in soy, which reduces the absorption of other nutrients (such as zinc, iron, calcium etc), however this is actually deactivated when soy is cooked or fermented – which is it always is when we consume it.
I can imagine you might be feeling a little overwhelmed with all of this information! That’s okay, it is a lot of rather complex science. To go back to the basics on what and how much soy is healthy to eat, I’ve summarised some take-home points below:
- Choose natural and minimally processed soy products – these contain a whole lot of fibre, minerals, vitamins and other nutrients and are associated with a range of health benefits. Go for tempeh, tofu, whole soybeans or edamame, soy milk and miso.
- Minimise highly processed and refined soy products – like any highly refined and processed foods, these contain little to no nutrients and are best kept to a smaller amount of our overall diet. These include textured soy protein (often found in vegan ‘fake meats’), soy protein isolate (often found in protein/energy bars and some soy milks) and other highly processed soy products.
- Choose organic and non-GMO where possible – genetically modified soy crops are resistant to toxic pesticides and herbicides, therefore very heavily sprayed with these.
- Eat fermented soy – such as tempeh and miso. These also contain probiotics for great gut health, are the most easily digested and are nutrient powerhouses!
- Moderation is key – as with every other food too! A serve or two of soy a day appears to be totally fine, and actually very beneficial for our health. Vary your diet with other plant protein sources, such as chickpeas, lentils, beans, quinoa and other whole grains, nuts and seeds!
There’s really nothing to be scared about when it comes to soy, the key is choosing the more wholesome soy foods the majority of the time, and (as always) focusing your diet on a variety of different plant foods to reap all the benefits of great health!