The Truth About Soy
There seems to be a never-ending debate about soy, with most people having very strong opinions on whether it's good or bad for you. So is soy evil, or is it healthy? Let's take a look at the science and find out!
There is a LOT of conflicting information, views and opinions out there on soy, I'm not going to lie. It can be terribly confusing and tricky to decipher fact from fiction, even in the world of scientific studies.
I'm going to start with the basics, by defining what soy actually is. A legume. A bean! Soy, in it's whole form is a soy bean, or edamame. From these beans, a whole variety of products are created: from minimally processed, more wholesome ones such as tofu, tempeh and soy milks, to ones almost unrecognisable as the plant food it once was, such as soy protein isolate, soy lecithin and other soy extracts.
When it comes to studies, most of them focus on one particular part of soy and whether this has any health risks or health benefits, as opposed to viewing soy as a whole food. These compounds are isoflavones, a form of phytoestrogen (plant oestrogen).
Do we ever eat isoflavones in isolation? I don't think so! And a whole, intact food with many other nutrients and compounds woking synergistically will act very differently in the body to a refined and isolated compound. Another important thing to note is that most studies are done in vitro (meaning, in a test tube) or in animals (who metabolise soy very differently to us!), so it's difficult and pretty much irrelevant to assume the same things will occur inside the human body...Other studies look at the effects of eating over 14 servings of soy per day, which is also just ridiculous and irrelevant.
The other VERY important thing to look at when reading studies is funding. If you take a look at studies supporting soy, often they've been sponsored by the soy industry. Whereas if you look at studies against soy, they usually have received funds from the dairy or meat industries. It's pretty obvious these industries would never release studies that make their own interests look bad, therefore studies are often very biased. Creating confusion around soy this way from animal agriculture industry funded studies means people most likely will stick to their current, animal-based, eating habits.
That's a lot to consider. So I am basing my conclusions on soy only on evidence that I feel is actually relevant, reliable and translatable to humans.
Does soy have 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 ACT like oestrogen in our human bodies?
Well, it turns out there are actually different oestrogen receptors in the human body, and isoflavones don't bind to all of them. Fun fact, the ones they bind to are called transactivates ER-beta, but you don't really need to know this! Anyway, because they selectively bind to receptors that are different from the ones 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 can 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. And soy definitely doesn't cause 'man boobs'...we'll leave that to the mammalian oestrogen found in animal products, such as dairy, which, unlike soy oestrogens, DOES have the same effects in our bodies as our own oestrogen hormone. Also, the majority of GMO soy (very highly sprayed with herbicides and pesticides) is fed to chickens, cattle and pigs, which are then also consumed by people!
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 a high in fibre, and the type of carbohydrate it contains is easily digestible. This helps feed our good gut bacteria and promote healthy bowels
Soy may reduce the risk of cardiovascular disease, as well as reduce LDL cholesterol levels and blood pressure
Moderate consumption of soy may be protective against breast cancer and endometrial cancer, as well as reduce the risk of breast cancer reoccurrence
Soy may reduce the symptoms of menopause, such as hot flushes
Soy does not reduce (or even effect) testosterone levels or sperm quality in any way. It may in fact lower the risk of prostate cancer by up to 50%
Soy has been shown to improve bone density and protect against osteoporosis
Soy appears to have no effects on the thyroid, as long as you are meeting your iodine needs (which is essential whether you eat soy or not!). However, it may reduce levothyroxine absorption (this is a drug often taken by people with hypothyroidism), therefore it is advised 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 your 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
So, I can imagine you might be feeling a little overwhelmed with all this information! That's okay, it is a lot of complex science. But to go back to the basics on what and how much soy is healthy to eat, I've summarised it below:
Choose mostly minimally processed soy foods - these contain a whole lot of fibre, minerals, vitamins and other nutrients and are associated with a range of health benefits. This includes tempeh, tofu, edamame, soy milk, TVP, soy yoghurt and miso.
Diversity is key - we know from the evidence that 2-4 serves of soy a day is totally fine, but a good variety of different foods and protein sources is always a good idea overall as well.
So there you have it. There's really nothing to be scared about when it comes to soy, and there are really only benefits up for grabs by including this wonderful food in your diet regularly!
I hope you found this post helpful, and feel free to leave a comment if you have any questions at all! xx
