Isoflavones: What are they?

Isoflavones are phytochemicals (bioactive plant chemicals) related to the more common antioxidant flavonoids found universally in plants, such as green tea, grape seeds, citrus peels, blueberries and ginkgo leaves. The isoflavones found in soy (also known as phytoestrogens) are some of the best-known and well-researched phytochemicals because they have structures similar to the body's natural estrogen.

Soybeans and soy foods contain three principal chemical types of isoflavones: genistein, daidzein and glycitein. From a dietary perspective, the total intake of isoflavones is more relevant than their chemical type. Another important factor is whether the soybean has been fermented. Fermentation of the soybean converts the isoflavones into their free form or aglycone form, which is more readily assimilated and bioactive in the body. If soy is ingested in an unfermented form, the assimilation of isoflavones may be inhibited by lack of gut microflora (the healthy bacteria naturally found in the digestive tract). A well-functioning digestive system containing an abundance of healthy microflora is necessary to convert these inactive isoflavones to their bioactive and readily absorbable form.

Generally, the concentration of phytochemicals in foods is low, yet soybeans contain large amounts of these particular isoflavone phytochemicals. The amount of isoflavones found in a soybean will vary slightly according to the variety of the soybean, where it is grown and how it is processed. Yet, most soy foods supply an excellent source of isoflavones, providing a range of 30 to 50 milligrams per serving. Just one cup of soymilk or tofu can contain enough isoflavones to exert a medicinal or physical effect.

Hormonal effects of isoflavones: What do they do?

Isoflavones have molecular weights and structures similar to the body's natural steroid hormones, such as estrogen. The pattern of isoflavonoid excretion in the urine is similar to that of the body's own estrogens. Therefore soybean isoflavones can act as estrogen mimics with between 1/50 and 1/100,000 the activity of the body's own estrogen. It appears that isoflavones, like other phytoestrogens, possess both estrogenic and antiestrogenic activity, which together can strike a biological balance. Although isoflavones are not to be considered a complete replacement for estrogen replacement therapy (ERT), they have been shown to reduce the occurrence and severity of hot flashes and may lower the risk of heart disease and bone loss.

Isoflavones could have a potential role in chemo-preventive therapy. Isoflavones help reduce the risk of certain types of cancer, such as uterine, breast and prostate cancer, because they have potential to lower an individual's lifetime exposure to natural or environmental estrogen (see Xenoestrogen table). Isoflavones compete for estrogen receptor sites, even changing the way estrogens are broken down.

Isoflavones also have many important non-hormonal properties such as potential growth-inhibitory properties. Isoflavones have been shown to effectively block enzymes that promote tumor growth, prevent the formation of blood vessels that feed cancerous tumors, and work as an antioxidant preventing the formation of oxygen-free radicals (highly reactive molecules that damage healthy cells).

Although studies on the benefits of isoflavones appear promising, what researchers still don’t know is how all the different isoflavones work in the body. The true tests of the theories about soy and isoflavones have not been carried out in large-scale and long-term human studies simply because the active compounds in soy, such as isoflavones, have only been researched over the last decade.

Isoflavones: When not to take them, what to watch out for

Researchers have voiced concerns that the consumption of large amounts of isoflavones may cause adverse health effects in infants and during breast-feeding. The major problem stems from the use of soy infant formulas, which contain soy protein isolates. A study published in Lancet, in July 1997, examined the isoflavone content of 5 major brands of soy-based infant formulas. The researchers estimated the daily exposure of infants to soy isoflavones was six to eleven times higher than the typical dose necessary to exert hormone-like effects in adults. A different study reported human breast milk from mothers consuming soyfoods provided substantial levels of isoflavones. Infant exposure to high levels of isoflavones may have significant risks to normal growth and development.

Over-consumption of soyfoods and isoflavones can have negative effects on thyroid health and decrease thyroid function, as well. Iodine deficiency greatly increases soy's anti-thyroid effect, so iodine supplementation is protective.

Also, the potential for interactions of isoflavones with medical treatments, such as estrogen replacement therapy or cancer therapy, is unknown.

Adding isoflavones to your diet: What is a proper dosage?

Research indicates soy isoflavones have several potential health benefits, exerting a wide array of effects, which appear to offer protection against cancer, cardiovascular disease, osteoporosis and other hormonal deficiency diseases. A safe range of isoflavones appears to be between 50 to 100 mg per day for an average adult. It is advisable that infants and young children avoid soyfoods containing isoflavones, and those with potential thyroid deficiency should keep their consumption to 30 mg per day or less. Yet, until isoflavone content of individual soy products is routinely listed, it is advisable to use only those soy products that provide this information. To ensure proper, high-quality bioactivity of the isoflavones, look for organic, non-GMO soyfoods that are also fermented.


RoseMarie Pierce

RoseMarie Pierce is a registered pharmacist, a co-partner in SunStreams Natural Living Store in Calgary and serves as technical advisor for Prairie Naturals Health Products

This article has appeared in, and is supplied courtesy of  VISTA Magazine