Isoflavones are secondary substances which plants manufacture for their own defence.  The soya bean is one of the richest sources of isoflavones. Soya isoflavones are especially valued in natural medicine for their light oestrogenal action. The oestrogen from a vegetarian source such as is found in soya beans restores the natural balance in women during and after the menopause.

The well-known symptoms during the menopause are caused by the low level of oestrogen. The production of oestrogen starts lessening in many women at the age of forty and stops entirely at the last menstruation about six years later. At that moment the hormone production in a woman has reached its lowest level and stays at that level till extreme old age. Lowering the oestrogen level can cause a number of unpleasant symptoms such as irritability, irregular sleep, dizziness, changeable moods and lack of concentration.

In Asiatic countries menopausal problems are an exception. Close research into this phenomenon shows that in these countries the soya bean is one of the most important foods and thus a concentration of isoflavones is taken in; an Asiatic woman takes in about 50 mg isoflavones in her daily diet. The isoflavone level in an Asiatic woman can be about 10,000 times higher than her European sister. Apparently the somewhat weaker vegetable oestrogen in the soya bean seems to compensate for the lessened oestrogen production in Asiatic women.