This ‘storehouse of nutritional riches’, as it has been described, is high in protein and contains all the essential amino acids in useful amounts. These amino acids are called ‘essential’ because the body can’t make them itself and relies on us eating them. Meat also contains all the essential amino acids but if you don’t eat meat, soy beans are the best vegetarian alternative.
Soy beans contain vitamin E, some of the B vitamins, magnesium, iron and zinc, although other components of the bean leave these last two poorly used. In their natural state, soy beans are also high in fibre, but most is removed in processed products such as soy milk and tofu.
While soy beans are much higher in fat at around 40%, than other beans which are around 2-14% fat, most is unsaturated, including some omega-3s. And being from a plant, they do not contain cholesterol.
What are phytoestrogens?
Phytoestrogens are substances in plants which act to mimic the female hormone, oestrogen. Soy contains phytoestrogens called isoflavones. Other types of phytoestrogens are found in whole grain cereals, nuts, seeds, linseed, lentils, chickpeas, kidney beans, tahini, hummus, alfalfa and extra virgin olive oil.
Genetically modified soy
Soy foods often state on their label that they are made from non-GM soy. Many soy bean crops in the United States are genetically modified to be herbicide-resistant. This means they can spray herbicide over the crop without killing the soy beans. GM soy is found in many foods such as margarine, mayonnaise, biscuits, potato chips and chocolate.
Foods sold in New Zealand that contain genetically modified ingredients must be labelled accordingly. Only GM ingredients that have been preapproved and safety assessed are able to be sold in NZ.
The bottom line
Soy by itself is not a magic food but can certainly be part of a healthy diet for both adults and children.
Soy is a complex chemical package containing hundreds of protective compounds enhancing each other in just the right way. We can’t assume they have the same effect on their own as when eaten with all the other nutrients present in the whole soy bean. So this is a situation where a whole food, rather than supplements, is the answer.
Isolating one substance out of a food is not necessarily the most beneficial to health. In fact, the health concerns about soy are not so much about the whole soy bean as the individual isoflavones. Soy foods themselves vary in the amounts of isoflavones and other nutrients they provide.
When choosing soy foods, eat 1-2 serves a day, favouring whole soy foods over added isoflavones or supplements. Also, try other foods containing phytoestrogens, such as whole grain cereals, lentils, chickpeas, fruit and vegetables.
But remember, we can’t simply pull soy foods out of the traditional Asian diet – low in fat, high in vegetable protein, eaten in small serves – and throw it in amongst our western pizza, pies, cakes and biscuits, and expect the same result.