Good Soy? Bad Soy?

The soybean has been hailed as a potential ‘superfood’ for the last four decades, with its potential advantages apparently ever increasing. However, not everyone agrees the soybean is the miracle food it’s portrayed to be.

Establishing the truth about the soybean’s health benefits is difficult due to the polarity of opinions available on this little bean. Possibly no other food has ever received the level of attention that the soybean has.

Both sides of the debate make claims about the soybean’s benefits or detriments, often using emotive language. From ‘superfood’ to ‘nature’s wonder food’ to ‘miracle food, or ‘a cut above the rest’, the ‘humble’ soybean has a lot to live up to. However, it’s also been referred to as having a ‘dark side’, being ‘more insidious than hemlock’, and as ‘the next asbestos’.

Each side maintains they have the evidence to support their arguments, often asserting that the opposition’s studies are flawed. Further, there are numerous claims and counter-claims that each side receives financial benefits from promoting their views.

On a nutritional level, soybeans are high in fibre, calcium, potassium, phosphorus, iron, phytoestrogens, unsaturated fats, all the B group vitamins, and protein. Soybeans are the only non-animal food source containing sufficient amounts of the nine-essential amino acids required to make a complete protein. Low in salt and saturated fats, soybeans are cholesterol-free, with high levels of complex carbohydrates.

Various studies have shown that soybeans reduce cholesterol, help control diabetes, protect against osteoporosis and heart disease, alleviate menopausal symptoms, lower blood pressure, as well as containing cancer-fighting properties.

With such an outstanding nutritional and health profile, what makes some people doubt the soybean is as beneficial as its advocates proclaim?

While there have been numerous studies undertaken to investigate the various potential benefits of soybeans, it would seem that conclusions are often drawn without considering all factors.

For example, statistics show that there are lower incidences of hormonal cancers, colon cancer, heart disease, and diabetes in Asian countries. Investigations linked the consumption of soy with these lower incidences of disease, without allowing for other aspects of Asian diets. Typically, Asian diets are higher in vegetables and fish, while lower in meat and saturated fats, as well as processed and tinned foods, than the average diet in the United States.

A meta-analysis of 38 separate clinical trials concluded that a daily intake of soy protein leads to an average decrease in serum cholesterol of 9%. This could potentially reduce the risk of coronary heart disease (CHD) by 18-28%, a positive finding considering that CHD is the main cause of death in many developed countries.

However, it is important to note that in most studies, soy replaced other meat-based proteins. Reducing consumption of animal-based protein may lead to lower cholesterol levels, without consuming soy. This forms part of the argument that the soybean isn’t necessarily the ‘miracle’ food it’s claimed to be, with other factors contributing to its apparent benefits.

Even soy advocates, such as John Robbins, maintain that life-style factors are important. In other words, simply adding soy to the diet, without adopting healthy habits, such as exercise, not smoking, and eating healthily, won’t necessarily improve issues such as high cholesterol and diabetes.

Phytoestrogen, a plant-based oestrogen found in high levels in soybeans, is perhaps the most controversial issue of the soy debate.

Excessive levels of oestrogen are known to increase the risk of uterine cancer. But one study showed that women who ate the most phytoestrogens had the lowest risk of uterine cancer compared to those who ate the least. Other studies have shown that phytoestrogens also reduce the risk of breast and prostrate cancer.

While it is unknown why this occurs, one theory is that phytoestrogens attach to cells with oestrogen receptors, such as uterine and breast tissue, blocking the effect of oestrogen, either made by the body or taken as a hormone replacement.

Some studies show that while phytoestrogens may prevent hormonal cancers, women with breast cancer may be at further risk from taking soy supplements, although evidence is both contradictory and inconclusive. Soy supplements are often highly concentrated, so should be avoided, but the Cancer Council NSW believes moderate consumption of whole soy foods is unlikely to be harmful.

Concentrated soy phytoestrogens may be problematic. One report from Italy in 2004, found that six women developed endometrial hyperplasia, an overgrowth of the uterine lining, which could progress to cancer, after long-term consumption of concentrated soy isoflavones. However, a normal dietary level of isoflavones, a form of phytoestrogens, doesn’t appear to cause endometrial hyperplasia.

Although, some opponents of soy claim that even dietary levels of soy oestrogens block ovulation, stimulating growth of cancer cells, and contributes to hypothyroidism.

The opinions of the effect of phytoestrogens on children from soy-based products are also divisive. For example, while soy advocates maintain that there are no negative effects on children given soy formula, some opponents claim that infants fed on soy formula receive oestrogens equal to five birth-control pills every day. But soy advocates argue that phytoestrogens are much weaker than the oestrogens in birth-control pills and react differently.

High levels of phytoestrogens may also cause a number of thyroid abnormalities, early puberty in girls and retarded physical maturation in boys. However, many children brought up on soy products, especially those children of vegan parents, do not seem to be any unhealthier than other children are. If soy-related problems do exist, other factors must be considered.

The type of soy food is also a significant issue. Initial observations based on Asian diets, did not necessarily consider the use of traditional preparation methods of soy, which vary greatly from western mass-production methods.

Some nutritionists, who are often described as being anti-soy, are not at all, but they’re against some soy products. One such person, Dr. Joseph Mercola, doesn’t recommend non-fermented soy products for cancer prevention, but believes that traditionally fermented soy products may help if added to a healthy diet.

Soy advocate, John Robbins also prefers fermented soy as well as whole soy foods, to soy protein isolates or concentrates, and other derivatives. Health bodies, such as Better Health, recommend whole soy foods, in preference to soy derivatives.

Many of the studies and trials undertaken have been on a small number of people over a short period. For example, when breaking down the meta-analysis of the 38 studies, there was only an average of twenty persons per study. Another study, involving the effect of UHT processing on soy beverages, only recruited 80 participants over four weeks, while a trial investigating the impact on bone loss on post-menopausal Chinese women used 90 participants over a six-month period. Should significant conclusions be made from small, short-term studies?

While, most studies recommend that further, longer-term investigations be undertaken on the benefits or detriments of various aspects of soy, it seems that there is no end of seemingly conclusive claims being made from inconclusive evidence.

Studies using various components of the soybean are necessary to determine the specific effects of each component, but it’s more significant to assess the effects of consuming typical soy products as part of the average western diet.

Results need to be explained simply, excluding the hype and emotive language, which may lead to inappropriate use of soy. Emphasis of any benefits of the soybean should be within the context of lifestyle.

Current evidence does suggest that there may be some benefits to including whole and fermented soy foods in a healthy diet, but no so-called ‘superfood’ can repair poor health while unhealthy habits continue.