One of the most commonly asked questions I get is regarding the health of soy foods. I either hear that someone would love to go vegan but wants to avoid soy (which is fine, but also not necessary), or that they wish they “could” consume it, but are worried about relying on it as a source of plant-based protein because of all the negative implications they have heard from someone, somewhere. Regardless, my answer is the same! The right types of soy are unequivocally, a healthful choice. I talk more about the right types below.
Let’s look at the evidence in regard to some major concerns:
Soy contains oestrogen: No it actually doesn’t. It does however contain phytoestrogens (beneficial constituents of plants, also found in flaxseeds). This type of oestrogen “imitator” is not bad, but indeed, beneficial, with its naturally occurring oestrogenic activity. They adapt to what the specific individual needs, raising or lowering oestrogen levels accordingly. Regarding female fertility, a large-scale study at a fertility centre demonstrated improved birth rates in females consuming soy and undergoing fertility treatment. A note on menopause, women dealing with hot flashes found relief from soy products according to this study.
Soy makes men grow breasts: Nooo! Men’s sex hormones, including testosterone remain unaffected by consuming soy products. This study concluded that soy does not “exert feminizing effects on men at intake levels equal to and even considerably higher than are typical for Asian males.” Soy does not adversely effect semen quality, and a study at Harvard University found soy intake had no effect overall on male fertility.
Just so we are clear on this topic, I’d like to point out the ludicrously of these claims by illustrating that the milk from a cow comes from a female animal that has just given birth. Not only is this a much bigger animal than us, with a different hormonal profile, but just as humans, when cows give birth, their oestrogen levels elevate. Therefore, it stands to reason that the concerning source of oestrogen in the diet is cows milk! And so far, I’ve just mentioned the natural oestrogen (due to their recent pregnancy)… think about the hefty doses of synthetic hormones dairy livestock are injected with to increase their milk production! This only adds to the oestrogen load of most cows milk. Yuk!
Cancer growth and recurrence: research appears to indicate soy consumption has a positive effect on preventing or slowing down the growth of cancer. Phytoestrogens (present in soy) act as antioxidants and have anti-proliferative properties to inhibit tumour growth. Among women with breast cancer, soy food consumption has been significantly associated with decreased risk of death and recurrence. This study suggests that greater consumption of isoflavone-containing foods is associated with a reduced risk of endometrial cancer in postmenopausal women. Other analyses have found that soy foods are protective against prostate cancer in men.
Bone health: I hear you, don’t we need dairy to protect against osteoporosis? No, we don’t, and evidence suggests that populations consuming higher amounts of cows milk actually have higher incidence of osteoporosis versus populations who don’t. There are a number of reasons for this, namely, the acidity of the milk causing greater calcium excretion from the body. However, I thought it apt to point out that whilst soy generally does contain less calcium, it contains triple the amount of magnesium, a vital mineral for bone maintenance. Indeed, the latest research suggests soy milk is actually much better for bone health. Interestingly, the beneficial isoflavones (types of phytoestrogens) in soy are thought to inhibit the breakdown of bones. For example the isoflavone Daidzein, is actually used to create the drug ipriflavone, which is used to treat osteoporosis.
Hypothyroidism and soy: Soy products do not cause hypothyroidism and hypothyroid adults need not avoid soy foods. However, the isoflavones in soy may potentially reduce iodine availability, required for healthy thyroid hormone production. It is therefore suggested that people who consume soy might need slightly more iodine in their diets (which we can get from sea veggies like dulse and nori).
***There is always conflicting evidence and debate around the statistical significance of the findings in such studies. However whether there is no benefit, little benefit, or substantial benefit, I am yet to find a negative finding regarding soy, and that should be the message we hear loud and clear.
At the end of the day, the fear around soy seems to stem from a few sources:
- The grouping of all soy together – the bad: i.e. concentrated soy proteins and soy-derivatives used to thicken or emulsify products (often non-vegan products too), GMO, non-organic, non-traditional varieties such as highly-processed faux soy meats + the good: i.e. traditional sources of soy, non-GMO and organic such as tempeh, tamari, miso, natto and even a little good quality tofu from time to time is ok. So too is edamame. Combining the good and the bad like this is akin to saying that the questionable ground meat in a fast food chain burger is the same quality as the meat from your local organic butcher (whilst I don’t think either meat is healthy, this is a helpful comparison!);
- Rare cases of harm due to consumption of ridiculously large amounts of soy on a daily basis;
- Similar to point 1 above, because soy is grown in ginormous quantities and added to absolutely everything, including often unhealthy packaged foods, it is viewed negatively, similarly to corn. Again, non-GMO and organic varieties in their wholefood form are fine!; and
- Poorly-conducted research based and/or articles by groups with vested interests e.g. the Weston A Price Foundation (WAPF).
Soy sources to include:
organic and non-GMO edamame and fermented sources such as tempeh, natto, miso, tamari (easiest to digest and assimilate). Whilst soy milk and tofu are more processed, organic varieties from time-to-time if you really enjoy them are not going to negatively impact your health and should not be feared.
I am not claiming soy to be a miraculous cure-all, I am simply pointing out that there is a lot of good evidence indicating its benefits, and that you should feel confident in including it as part of a plant-rich varied diet (if you so choose).