Soy protein is often considered an alternative to meat and soy has crept into much of the food we consume, often labelled as textured vegetable protein. Soy is available as a range of products that can generally be classified as oils and non-oils, the latter including products such as soy milk and substitute meat products. Such products have become popular, based to some extent on the large body of research that purports to show benefits to the consumption of soy. In this regard epidemiological studies show that certain Asian cultures have lower rates of certain cancers, particularly breast and prostate cancer, something which has been attributed to their consumption of soy. However, the cause and effect of this association are not easy to identify as Asian cultures have quite different diets and lifestyles to Western counterparts and so confounding variables could explain this association. As well as epidemiological studies a vast amount of clinical trials have purported to show benefits to soy consumption for humans.
It is often stated that the Asian populations that shown lower rates of breast and prostate cancer are protected by their high consumption of soy. As stated previously, the cause and effects of this association is not clear, and so no firm causal relationship can be established. However, it is also untrue that Asian populations eat large amounts of soy. Generally those populations that have traditionally consumed soy eat only small amounts as a condiment. In particular, products such as miso, tempeh, natto and tamari as well as other fermented products are part of these traditional diets. The fact that the total intake of such populations may be as low as 10 grams a day, and that the products are fermented are the salient points. Fermentation is necessary because soy, as with all legumes, contains a number of proteins that can adversely affect human metabolic regulation. Many soy products that are sold to Westerners still contain these proteins in their active form because the products have not been fermented to denature their structure.
Proteins are rated based on their ability to supply the essential amino acids for human needs. In this regard proteins such as egg and whey are rich in all the essential amino acids that are required to synthesise human proteins and so are given values of close to perfect (100). Other proteins are judged against these standards and generally all animal proteins score highly. Plants have quite different physiologies to animals and this is reflected in different amino acid ratios in their tissues. Most vegetable proteins have amino acid profiles that are not as able to supply the essential amino acids for human requirements. Most grains for example are low in the essential amino acid lysine, and consumption of grain alone would therefore produce a lysine deficiency. Soy is a legume, and like all legumes is low in methionine and cysteine, which lowers its usefulness to human needs somewhat. Soy is considered by some to be as complete a protein as meat, but this is simply not true unless sulphur amino acids are supplied from other sources.
Another problem with soy is that around 90 % of the soy production in the World derive from genetically modified sources. It is becoming increasingly difficult to discern non-genetically modified soy from genetically modified soy as labelling and ingredient laws become more convoluted. For this reason consuming soy may increase the risk of inadvertently containing genetically modified organisms for those who wisely wish to avoid them. The oestrogenic compounds belonging to the isoflavone group of chemicals may also be problematic in both men and women. While certainly some studies have shown limited benefits to isoflavone consumption, many studies have shown possible deleterious effects. As with all oestrogenic compounds, isoflavones have the potential to disrupt hormonal balance and reports suggest they may actually increase breast cancer rates when given as in a supplemental form. It is therefore hard to recommend soy, especially when other more nutritionally sound proteins are available.
RdB
