Soy comes from the soybean. Soy has become an area of controversy in recent years, with some thinking it’s a nutritious addition to the diet, while others think it’s something that should be avoided.
Soybeans have traditionally been a big part of the Asian diet in the form of tofu, natto, miso and tempeh. In the Western diet, soy also plays a big role. However, in this case, soya is more commonly processed into soyabean oil, which is used in many highly processed foods.
Like anything, it’s important to take a balanced view and in order to do that, you need to weight up the pros and cons.
It’s one of the few vegan protein sources that’s classified as being a high biological value (HBV) source of protein. HBV proteins contain all the essential amino acids (these are the amino acids our body can’t make, so we need to get them from our diet). This means foods such as tofu can be a really good protein source, especially for those who are following a plant based diet or vegan diet.
Research also suggests that soy consumption may have a positive effect on bone mineral density and bone health, as it has been shown to increase bone formation and decrease bone breakdown. This could mean that soy consumption could be a beneficial food for those at risk of bone diseases such as osteoporosis and osteomalacia.
Soy consumption has also been associated with improved cardiovascular health. A 2017 meta-analysis by Yan et al., looking at the association between soy intake and CVD risk, found that consumption of soy foods was associated with a reduction in the risk of coronary heart disease, stroke and CVD. However, it’s worth noting that this was an analysis of observational studies which just shows an association, not a cause-effect relationship.
Men who are at risk of prostate cancer may benefit from consuming soy products. A 2018 systematic review and meta-analysis found that there was a significant association between consuming soy foods and a lower risk of prostate cancer. However, the possibly protective effect has not been seen in men who already have prostate cancer.
Soya is also a source of a group of antioxidants called isoflavones. These include genistein and daidzein. They are sometimes referred to phytoestrogens as structurally, they are quite similar to estradiol, which is a form of oestrogen. This means that soy isoflavones can reduce some symptoms of menopause, which are usually driven by lower levels of oestrogen in the body. Soy isoflavone supplements have been shown to reduce the number of hot flushes experienced by women going through the menopause.
One concern surrounding soya consumption is a possible reduction in testosterone levels in men. And theoretically, this may be true as soy can inhibit enzymes involved in testosterone production. Soy can also have oestrogenic effects which could also have a negative impact on testosterone levels. However, this doesn’t seem to occur in reality when men have a low to moderate intake of soy. A 2014 meta-analysis by Hamilton-Reeves et al concluded that clinical studies which had been carried out on soy intake in males showed no significant effect on total testosterone, free testosterone, or sex-hormone binding globulin (SHBG). However, there are case reports of soy negatively interfering with testosterone production in males with extremely high intakes.
Another concern is a possible increase in the risk of women developing breast cancer. This is because soy isoflavones can lead to increased estradiol concentrations, which is a form of oestrogen. And research has shown estradiol concentrations to be associated with an increased risk of breast cancer. So you would think that soy isoflavones could be associated with a small increase in the risk of breast cancer. However, this has not been the case in human studies. This isn’t to say that soy isoflavones aren’t associated with an increased breast cancer risk, but that it doesn’t seem to be as concerning as you may think. In fact, some studies are showing that it may actually be associated with decreased breast-cancer incidence and mortality.
A drawback to consuming soya is the presence of anti-nutrients. Anti-nutrients are compounds which impair the digestion and absorption of valuable vitamins, minerals and protein. Examples of anti-nutrients found in soya include tannins, trypsin inhibitors and phytates. While soaking can reduce the levels of some anti-nutrients such as tannins, it has little effect on phytates, unless soaked for very long periods.
Soy has many benefits to its use but there are still questions about its effects when consumed in high quantities. If you do choose to consume soy, choose minimally processed options such as natto, tempeh and tofu.