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Health benefits of Soy

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The soy story, All you need to know, the history, the benefits and the research of this interesting legume.

Benefits of Soy and Soy Milk

Touted 10 years ago as a superfood that could reduce the risk of heart disease and osteoporosis, soy remains controversial. Cindy Williams and Fiona Carruthers outline the latest research into its health properties

ORIGINATING IN NORTHERN China and a staple of Asian diets, the soybean plant wasn’t embraced by the Western world until after World War II, when the USA recognised its roots were full of nitrogenous bacteria that replenish soil. This made it ideal to plant in rotation with maize, a greedy plant that sucks nutrients from the soil. Soy soon became a major crop in the USA, mainly for animal feed and to produce soybean oil.

What intrigues nutritionists is the soybean itself. Known as a “storehouse of nutritional riches”, soybeans contain more protein than any other legume – and it’s high-quality protein, meaning it contains all the essential amino acids (these must be obtained from food) and is similar to animal protein.

While soybeans are higher in fat than other beans, they’re still low in fat compared to many other food products and they
contain mostly “good” polyunsaturated fat, including omega-3. Being a plant food, soybeans contain no cholesterol.

In their natural state soybeans are high in fibre. However, most of this fibre has been removed from processed products such as soy beverages and tofu. Soybeans contain vitamin E, folate, magnesium, zinc and iron.
They’re also rich in phytoestrogens (plant oestrogens), in particular the health-boosting isoflavones genistein and daidzein.
Based on the scientific evidence available, there are several areas in which soy foods can provide health benefits, while in other areas more research is needed.

Cholesterol & heart health

Currently, there’s little doubt that soy, specifically soy protein, plays a role in heart health.
Research shows diets high in soy protein can lower blood levels of “bad” LDL cholesterol and maintain levels of “good” HDL cholesterol. The reason for this effect is still being studied, but it’s thought the isoflavones that occur naturally in soy protein may play an important role.

A US study showed that when soy protein containing high levels of isoflavones was consumed, a significant reduction in blood cholesterol levels was seen. If the isoflavones were at low concentrations in the soy protein, there was no reduction in cholesterol levels. Interestingly, the same benefit is not seen when isoflavones are consumed on their own as a supplement.

You need to consume about 25 grams of soy protein each day for this benefit.
The isoflavones in soy protein may protect the heart in other ways. Isoflavones are antioxidants and they help counteract the build-up of cholesterol in the blood vessels, reducing the risk of blood clots and heart attack.
In addition, the combination of soy protein, isoflavones and soy fibre has been shown to reduce homocysteine levels, a key marker of heart disease risk.

In the USA and UK, food products containing a certain amount of soy are allowed to make health claims stating they can help lower cholesterol levels and prevent heart disease.
However, such health claims on soy food products are not permitted in Australia.

Breast cancer

Lower rates of breast cancer have been observed in some Asian countries and this has led scientists to investigate the link between soy and breast cancer.
Some breast tumours require oestrogen to grow, and soybeans contain phytoestrogens, which have the ability to interact with the actions of oestrogen.
Animal and test-tube studies support soy’s anti-cancer effect, but human studies are not so
convincing. According to The Cancer Council NSW, an overview of the current human studies suggests “a high consumption of soy foods may lower the risk of breast cancer, but only a little”.
More studies on the effects of soy on breast cancer prevention are needed. However, from the evidence to date, it’s believed moderate consumption of soy foods (one to two serves per day) combined with a balanced diet is unlikely to have adverse effects.

Soy supplements containing high levels of soy or soy isoflavones are not recommended as there is no evidence to suggest they are effective in cancer prevention.
For women with breast cancer, a diet high in soy and phytoestrogens has not been proven safe, however, The Cancer Council NSW states that “moderate consumption of soy foods, as part of an overall healthy eating plan, is unlikely
to have any harmful effects”.
Women with hormonesensitive breast cancer are usually prescribed the drug Tamoxifen, which blocks the actions of
oestrogen, thereby reducing or stopping the cancer growth. The impact of soy foods on the actions of Tamoxifen is still unclear.

Soy supplements have not been tested for safety in women with breast cancer or who are taking Tamoxifen, so The Cancer Council NSW recommends “women with breast cancer avoid soy and phytoestrogen supplements and to not suddenly increase the amount of soy phytoestrogens in their diet”.

Menopausal symptoms

Asian women report lower rates of menopausal symptoms such as hot flushes and vaginal dryness than Caucasian women. Researchers have questioned if this may be attributed to their soy intake, and evidence to date suggests soy
isoflavones may be involved.
During menopause, oestrogen levels drop, causing uncomfortable symptoms. It’s thought the isoflavones in soy act as a weak form of oestrogen, functioning| as a replacement for some of the oestrogen lost during menopause. However, most studies involving soy/isoflavones and menopause have seen similar effects in both the control group (not taking soy/isoflavones) and the treatment group (consuming soy/isoflavones), which suggests more research is needed to provide conclusive evidence for the role of soy in alleviating menopausal symptoms.

Osteoporosis

As we age, our bones become more brittle from calcium loss.
One in two Australian women and one in three Australian men over the age of 60 will suffer from osteoporotic fractures as a result.
The prevalence of fractures in Australia is higher than in Asian countries, and one influential factor is believed to be diet, in particular the type of protein consumed.
Current evidence suggests soy protein could play a beneficial role in bone health compared to animal protein, as it helps prevent calcium loss from bones. Bone mass is maintained by the hormone oestrogen, and because soybeans contain phytoestrogens, it’s believed they can help improve bone density and maintain bone health. Despite these findings, it’s not known if soy protein and isoflavones can prevent bone density loss over several years and therefore reduce the risk of fractures.

Soy-based infant formula

Breast milk is best, but a medical practitioner may be compelled to recommend soy-based infant formula for any number of reasons.
Unlike adults, for whom soy contributes a small part of the diet, infant formula represents all or a substantial part of the diet for the first year of life. Questions have been raised about the possible effects of soy-based formula on infants, given the high levels of phytoestrogens they’re consuming.

While isolated cases of goitre have been reported (quickly resolved when the infant stopped taking the formula), there is no hard scientific evidence to suggest that soy-based formula has an adverse effect on infants.
To date, a review of clinical studies concludes soy-based infant formula supports normal growth and development. However, as more research is needed, the Royal Australian College of Physicians recommends parents use soy-based infant formula only under the direction of their doctor or qualified health practitioner.

Part of a healthy diet Soy is a complex chemical package containing hundreds of protective compounds. Isolating
certain compounds from a food is not necessarily beneficial and studies have found soy supplements to have little effect.
Most of the health benefits reported have resulted from eating whole soy foods. These vary in the amounts of isoflavones and other nutrients they provide, but research shows one to two serves of soy foods each day, as
part of a healthy diet, to have no adverse effects.

With our Western culture of eating foods that are high in saturated fat, sugar and salt, we cannot simply adopt the soy foods found in the traditional Asian diet, which is low in fat, high in vegetable protein and eaten in small serves, and expect the same results. Soy by itself is not a wonder food, but it can be part of a healthy diet for both adults and children.