The soybean (Glycine max) is a legume in the plant family Fabaceae. For centuries, Asian countries have used the soybean as both food and medicine. Today, soy products such as soy powder, tofu, soymilk, soy protein, soy nuts, miso and tempeh can be found in most countries and act as an important part of peopleâ€™s diets.
Soybeans are an excellent source of plant protein that many consider to be equal in quality to animal protein but with the added benefit of possessing negligible amounts of cholesterol. However, the protein from soybeans is less able to be absorbed by the body than soybean products that have been more highly processed, such as protein powders and tofu.
A revered crop
Soybean use can be traced back as early as the 11th century BCE in China. In 2838 BCE, the Chinese emperor Cheng-Nung honoured soy as one of the five sacred crops (the others being rice (or hemp), wheat, barley and millet). So revered were these crops that the ancient Chinese gave them their own god, Houji.
Itâ€™s also believed that soy is one of the first crops to be cultivated and domesticated by the Chinese in the eastern region of the country. Over the centuries, soy was introduced into nations such as Japan, Vietnam, Malaysia and India. Records indicate that Europe started importing soy (as soy sauce) in the 17th century, while America only â€œdiscoveredâ€ soy after soybean plants, initially used as ballast aboard a ship, were planted in the 19th century.
An American chemist, G.W. Carver, discovered that, not only was soy an excellent source of protein and oil, but if farmers rotated their normal crops, such as corn or cereals, with soybeans, a better crop was produced. This is due to soy and other legumesâ€™ ability to introduce nitrogen and other nutrients into the soil.
What are soy isoflavones?
Isoflavones are a class of chemicals found in plants. The highest concentration of isoflavones with medicinal properties, genistein and daidzein, is found in soybeans. In a typical Asian diet where soy products are a food staple, 20â€“80mg of soy isoflavones are consumed on a daily basis.
Research has determined that soy isoflavones possess antioxidant properties that can protect our cardiovascular systems. Perhaps itâ€™s better known that isoflavones are also a type of phyto(plant)-oestrogen that can play a food-medicine role in the prevention of osteoporosis and menopause symptoms.
Soy as medicine
A plant hormone
As a woman ages, the hormone oestrogen decreases. To compensate, her body will increase the production of lutenising hormone (LH) and follicle stimulating hormone (FSH). Symptoms of this change in hormone levels, which we refer to as menopause, are hot flushes and night sweats.
The idea that soy may play a role in addressing menopause symptoms came with the realisation that Japanese women, who have a 50â€“100 times greater intake of soy isoflavones than in traditional Western diets, have a tenfold lower incidence of menopause symptoms. Only 14 per cent of Chinese and Singaporean women experience hot flashes during menopause compared with 70â€“80 per cent of women in North America and Europe. This is believed to be due to the effects of soy phyto-oestrogens.
Phyto-oestrogens are found in foods such as soy that are converted into a weak oestrogen-like substance. While weaker than the oestrogen found in a womanâ€™s body, phyto-oestrogens can still link with oestrogen receptor sites, which blocks LH especially from entering the system. As a result, menopausal symptoms such as hot flushes are reduced.
Improves bone health
Soy appears to have the ability to enhance bone density. Daily consumption over six months of a soy protein isolate containing 90mg of soy isoflavones produces significant improvements in spinal bone mineral density in post- menopausal women.
Soy isoflavones and soy protein are not just for menopausal women â€” they are also excellent for the health of our hearts. Soy isoflavones such as genistein can stop atherosclerosis (plaque in the blood vessels) from forming and reduce existing atherosclerotic plaque.
Individuals who take 31â€“47g of soy protein daily have been found to have a 9 per cent reduction in total blood cholesterol, a 13 per cent reduction in LDL cholesterol and an 11 per cent reduction in triglycerides, thereby greatly improving both your blood lipid profile and your heart health.
Taking soy isoflavones
Suggested dosages for the treatment of hot flushes in menopause is 60â€“80mg/day, osteoporosis is 90mg of soy isoflavones/day and, for lowering cholesterol and improving vascular health, is around 30â€“50g of soy protein/day.
A word of caution
Taking levothyroxine (a thyroid medication) with a soy protein dietary supplement has the potential to decrease the absorption of the drug and may result in the need to take higher oral doses for a therapeutic effect.
Currently a full-time mum, Caroline Paul is a qualified naturopath specialising in research.