Just how healthy is soya?
Posted Wednesday, September 19 2012 at 01:00
Everything seems to be fortified with soya nowadays: beverages, flour, margarine, oil. I could go on. It appears to be the perfect food: it balances hormones, strengthens bones, prevents heart disease, and wards off cancer, and is good value for money.
So why would I not give it to Baby Mukherjee?
Well, soya contains certain “anti-nutrients”, and what most people do not realise is that in Japan, where the health benefits of soya have been most widely documented, the soya they eat is not like the kind we do.
The Japanese generally eat soya that has these anti-nutrients deactivated, either through fermentation, (such as in miso, soy sauce, tamari, and tempeh) or through a process called precipitation. This is how we get tofu and soya bean curd.
Other than tofu, we do not really get the other kinds here. Does that mean that we should avoid soya altogether?
Before we go there, some advice: As with many issues, people have their own agenda when pushing a product. Almost every study is funded by a party with vested interest in the results, whether it is the large soya companies advocating genetically-modified soya or pharmaceuticals trying to criticise any natural, and therefore unpatentable, products. This is what makes unbiased research so hard to come by.
With this in mind, here are the facts.
Soya is a hormonal superfood. As one of the richest sources of isoflavones, eating soya can help to counter our exposure to oestrogen-like, hormone-disrupting chemicals in our environment, which can contribute to conditions like polycystic ovaries and breast and prostate cancer.
In the case of menopause (when oestrogen levels fall), they act as a mild oestrogen, helping to relieve symptoms. Other reports claim it lowers cholesterol, reduces the risk of osteoporosis, and helps athletes build muscle.
So far, so good. What about these anti-nutrients? Are there really that many? The first are a group of substances called phytates, which can block the absorption of vital minerals such as calcium, magnesium, and zinc. It is this poor assimilation that helps to explain why diets high in phytates have caused growth problems in children.
Next are enzyme inhibitors, which block the digestion of protein, thereby causing digestive problems. While these are also present in other legumes, soya beans also contain haemagglutinin, a substance that encourages red blood cells to clump together, thus reducing oxygen uptake.
The good news is that both the enzyme inhibitors and haemaglutinin are deactivated when soya is fermented and precipitated.
Soya is also a common allergen. While many use soya milk as an alternative to dairy milk, it is likely that they may be sensitive to soya, too. Remember that while soya has been eaten for thousands of years in continents like Asia, it is relatively new elsewhere, making chances of intolerance higher.
What about its influence on fertility? Studies (as well as my own patients) have reported that drinking soya milk during pregnancy can hinder breast milk production. Another study by the Harvard School of Public Health found that soya consumption can significantly reduce sperm count.
Evidence has also shown that infants who have been given a soya formula instead of breast milk have a huge chance of developing an underactive thyroid. Soya can also adversely affect thyroid function in adults.
There is also increasing evidence that girls who have been fed soya for nine months or more go through early sexual development, some as early as five or six years old, sometimes earlier. In young boys, the problem has generally been linked to the appearance of breasts at puberty, and testicles that do not develop.
So, do we continue to take, or do we avoid soya? Like with so many things, it comes down to moderation. The Japanese generally only eat about three teaspoons of soya daily — not very much, and the right kind. Since we live in Kenya, this means eating a little tofu a few times a week. As for children, I would refrain from giving them any soya.
The writer is a clinical nutritionist and certified by the Nutritional Therapy Council in the UK. Please direct any questions about family nutrition to her on firstname.lastname@example.org