A chewing gum which the makers say can help enhance the size, shape and tone of the breasts has proved to be a big hit in Japan.

B2Up says its Bust-Up gum, when chewed three or four times a day, can also help improve circulation, reduce stress and fight ageing.

The gum works by slowly releasing compounds contained in an extract from a plant called Pueraria mirifica.

In theory, this helps to keep the muscle tissue in good order.

Pueraria mirifica, also known as Kwao Krua, is a species found in Thailand and Burma.

It has long been used by indigenous hill tribe people as a traditional medicine.

The plant's underground tubers contain a number of chemicals called phytoestrogens - natural compounds which mimic the effects of the female sex hormone oestrogen.

These include miroestrol and deoxymiroestrol, which are believed to exert a particularly strong effect, as they are very close in chemical structure to oestradiol, the main human oestrogen.

B2Up says that it is the effect of these two chemicals, coupled with a third phytooestrogen isoflavone, which makes its gum so effective.

It cites tests carried out by Thailand's Chulalongkorn University which found Pueraria mirifica therapy was able to enhance breast size by 80%.

Further tests carried out in England found that the plant had a beneficial effect on the skin, and hair, as well as the breasts.

The company also markets different Pueraria products, including pills, and tea.

The gum, which comes in rose flavour, has proved so popular that there are plans to start selling it in convenience stores.

Scepticism

Claire Williamson, of the British Nutrition Foundation, said research had suggested phytoestrogens may be beneficial in post-menopausal women in terms of reducing menopausal symptoms, and may also have beneficial effects on risk factors for heart disease and osteoporosis.

A role in breast cancer has also been suggested.

But she said research had suggested that isoflavone supplements are not as effective in managing menopausal symptoms as isoflavone rich foods such as soya.

Furthermore, consumption of isoflavones may need to be life-long in order to have beneficial effects on postmenopausal symptoms.

"So there is clear evidence of the potential health benefits of consuming isoflavone-rich foods such as soya, however consumption in the form of a gum has not been extensively studied and such products may be simply another food gimmick."