Is Soy Bad For You?

9 June

Soy has been demonised for a number of years now, with fears about GMO soy having the potential to destroy our health leaving people scared to eat it at all. But is the fear-mongering around soy substantiated? In this blog post we take a look at soy, the pros, cons and controversies, and what the evidence says.

What is Soy?

Soy is a legume, similar to lentils and chickpeas, that has been consumed for centuries in China and other parts of Asia, where it is considered a staple food. It is rich in protein, fibre, iron, magnesium, B6, vitamin C and calcium, and is commonly pressed and consumed as tofu or tempeh, but can be consumed as a whole legume, too.

Commonly consumed sources of soy include:

Tofu
Tempeh
Soy sauce
Textured vegetable protein
Soy protein powder
Soy and its isolates are also commonly used in many different processed food products like chips, lollies, chocolates, and more.

Fears About Soy

So, what is it about soy that people are worried will affect their health and where did this fear come from? There are two main fears about the dangers of soy: phytoestrogens and GMO.

Soy Phytoestrogens

Soy is rich in phytoestrogens, plant compounds that are structurally similar to (but are not the same as) the oestrogen our bodies produce. Soy phytoestrogens get a bad wrap, but much of this negativity is really due to a misunderstanding on how phytoestrogens work. Many believe phytoestrogens exclusively increase oestrogen activity in the body, but they are actually oestrogen modulating. This means that if you have high oestrogen levels, they can help to reduce oestrogen activity, and if you have low oestrogen levels, they can help to gently alleviate this. They are able to do this because they can bind to oestrogen receptors in our bodies, but they only have a very, very weak effect. They are very different to xenoestrogens - the compounds found in plastics - which definitely do have a negative effect on our hormonal health!

The amount of phytoestrogens needed to exert any kind of health effect is around 50mg per day. People in Asian cultures eating a traditional diet typically eat 15-50mg per day, while people in the West often eat as little as 2mg per day. Additionally, in Western diets the majority of phytoestrogens aren’t derived from soy products, but come from other legumes, whole grains, and vegetables. How strong the effect of these phytoestrogens are also depends on both our genes and our gut microbiome. Studies suggest that even with high consumption of soy isoflavones, we need certain microbes in the gut to convert the isoflavones into their active forms - microbes that many people in the West have low levels of (or lack altogether).

What About the Evidence of Soy Isoflavones Being Harmful?

There are some studies out there that suggest that the phytoestrogens in soy foods may have a damaging effect on oestrogen and testosterone levels, but these studies are typically done on non-human animals and administer phytoestrogens via injections in very high doses, so the results really don’t reflect typical consumption patterns of soy. It’s really not relevant then for us to be using these studies to decide that soy is harmful, when so much great evidence of the benefits of soy consumed as part of a healthy, varied diet suggest it is actually very beneficial to our health.

GMO Soy

GMO soy is an issue with regards to food safety and can potentially leave us exposed to health issues, however it is not the soy itself that is the harmful part. GMO foods are developed to be resistant to herbicides like Round-Up, so they can be heavily sprayed without damaging the plant. Unfortunately, this means leftover herbicide residue on the foods we consume. We can avoid GMO soy by choosing organic varieties of soy beans, tofu, and other soy food products. As a large percentage of GMO soy is used as animal feed for animals in meat production and agriculture, choosing organic meats will also reduce your risk.

Health Benefits of Soy

There are many great health benefits associated with regular consumption of soy foods. Whilst soy might be a bit of a feared food here in the West, it is one of the most popularly consumed foods globally, and certain cultures such as Japan, where soy is a regular part of the diet have demonstrably lower rates of many of the chronic health conditions that are so common in Western cultures.

Just some of the health benefits of soy include:

Antioxidant and cell-protecting effect
Prevents cardiovascular disease
Reduced risk of certain cancers, such as breast cancer
Improved skin health

Effects of Soy on The Brain

Interestingly, research has found that genistein, one of the phytoestrogens found in soy, might actually have a neuroprotective effect on the brain. Studies have found the consumption of genistein increases the production of an important chemical in the brain called brain-derived neurotrophic factoer (BDNF). BDNF is responsible for protecting brain cells and promoting neuronal plasticity, the changeability of brain cell connections that allows us to learn new things.

Soy and Fertility

The phytoestrogens found in soy can also have beneficial effects on fertility, including improving egg maturation and quality, improving the preimplantation phase of pregnancy, and stimulating progesterone production in the ovaries. As for males/ people assigned male at birth? The good news is soy consumption does not affect their fertility. A 2021 meta-analysis looking at the results of 38 clinical studies found soy did not affect testosterone or oestrogen levels in men.

Soy and Menopause

One of the areas where I really see the benefits of soy in action in clinic is during perimenopause. During the perimenopausal transition and the onset of menopause, oestrogen levels drop to much lower than before, which is one of the primary drivers of perimenopause symptoms. Regular consumption of soy, with its oestrogen-modulating compounds, can help to gently lift oestrogen activity and reduce the severity of perimenopausal symptoms. Multiple studies show that the use of soy phytoestrogens during this life stage can help with symptoms like:

Urogenital symptoms
Sexual function
Hot flushes

When to Avoid Soy

I will say that when it comes to soy, whole food soy products - foods like soy beans, edamame, tofu, and tempeh, are far superior to highly processed and refined soy products like soy protein powders. Soy protein isolates (SPI) are not the same as whole food soy and can be derived from GMO sources. SPIs are also processed through the use of hexane, a solvent and cleaning agent that is also a known neurotoxin. Unfortunately due to a lack of testing and data, it’s unclear exactly how much residual hexane remains in SPI products produced this way. This is yet another reason to choose organic products, which do not use hexane in the manufacturing process.

There are also some instances in clinic where avoiding soy can be beneficial or necessary.

If you have an allergy or intolerance to soy, you need to completely eliminate all soy and soy byproducts from your diet. This means carefully checking labelling of all food products, because soy is quite a common ingredient in processed foods.

If you have hypothyroidism or a low-functioning thyroid, it is best to avoid soy or reduce or intake of soy, because soy contains compounds called glucosinolates, which can slightly suppress thyroid function if eaten in high quantities. These are similar to the compounds found in other foods like broccoli and raw kale, which have similar effects on the thyroid. People with low functioning thyroid can still enjoy fermented soy products like tempeh, as the fermentation process largely inactivates the thyroid-suppressing compounds.
Some people with inflammatory conditions like Crohn’s disease and rheumatoid arthritis do well avoiding soy protein isolates from their diet. This is likely because of the anti-nutrients like phytates that can be more concentrated in soy protein isolate compared to whole and fermented soy foods.

If you have an “oestrogen-dominant” condition, such as endometriosis or PMS, you can still eat soy!! As discussed above, the soy phytoestrogens do not worsen oestrogen dominance and in fact they will have a slightly anti-oestrogen effect, helping to keep your oestrogen dominance in check.

How Often Should I Eat Soy?

Soy is a rich source of so many great nutrients and a wonderful protein option for those on a plant-based diet. Unless you have a condition that benefits from low or no soy, consuming tofu or other organic soy products a few times a week is great. I typically consume soy in one form or another most days, whether that's in soy milk (hello, Bon Soy!) or organic tofu in a curry or stir fry.

When choosing soy products, always choose organic options where available. I would also recommend steering clear of soy protein isolates, which includes a lot of soy protein powders (although some are made using whole soy beans). If you’re after a quality plant-based protein powder, I recommend using plain-old hemp protein powder.