10:43 PM Ian
Ahh, the Grapefruit Diet - what bitter memories
it invokes. That unmistakeable acid tang and the endless tangle of pith and fibre winding through the teeth - not to mention the twin sensations of deprivation and constant hunger.
For so many women, losing weight in the Seventies and Eighties was synonymous with eating grapefruits by the score.
The diet - beloved by celebrities such as Brooke Shields - claimed that enzymes in the fruit could boost metabolism and break down fat; would-be slimmers were told to eat no more than 800 calories a day (about half that recommended for steady weight loss) and to precede every meal with half a fruit.
Yet even though the results were always temporary, and nutritionists warned that the science was poor, and all we were losing was water, many felt the ends justified the means.
The diet was fast and - being fruit-based - safe. Yet, a study now suggests that the grapefruit - Citrus paradisi - could have been harming a whole generation of women.
The report, from the Universities of Southern California and Hawaii, published in the British Journal of Cancer, states that eating it can increase the risk of breast cancer by nearly a third. The fruit is believed to boost blood levels of oestrogen, the hormone associated with increased risk of the illness.
The researchers claim that post-menopausal women who eat as little as one quarter of a grapefruit per day (or juice equivalent) could see their chances increase by 30 per cent. Most dieters would have been eating at least six times that amount.
This is not the first time grapefruit has been implicated in a health scare.
We know that grapefruit contains substances called naringin, bergamottin and dihydroxybergamottin which can speed up or slow down how drugs are metabolised in the body by inhibiting an enzyme (CYP3A4) in the stomach.
Anyone taking immuno-suppressant drugs knows to avoid grapefruit; other drugs known to be affected include anti-depressants such as Seroxat, statins such as simvastatin; sedatives such as Valium; antihistamines such as Claritin; blood pressure tablets such as Felodipine; and even Viagra.
CYP3A4 is also known to influence the metabolism of oestrogen and the American researchers had wanted to see if this resulted in higher levels of oestrogen and therefore an increased risk of breast cancer. Even so, their findings surprised them.
''We think of all fruit as benign,'' says Catherine Collins, chief dietician at St George's Hospital in London. ''But it's much more complicated than that. Fruit and vegetables provide us with vitamins, minerals and fibre but they also deliver plenty of phyto-chemicals, the power of which we just don't understand yet."
Collins explains that the bitter taste of raw cruciferous vegetables such as broccoli or sprouts is caused by a minute quantity of cyanide in the cells, released when we crunch them. ''The cyanide travels to our liver which it stimulates to produce detoxifying enzymes.
These clean up the cyanide cells but also any other toxic substances present at that time in our bodies.''
Collins says that the substance in grapefruit responsible for increasing levels of oestrogen in the blood will be just such a chemical, and one of thousands of biological active substances in the fruit. ''It might be harmful to some but it might be useful to others - it could even act as a sort of natural HRT, as soya does.''
Breast cancer broadly divides into two types: oestrogen receptive and non-oestrogen receptive. So in the latter 50 per cent of cases increasing levels of oestrogen are irrelevant. It's also of little concern to any pre-menopausal women or those taking HRT or the contraceptive pill, who produce high levels of oestrogen already.
More affected are post-menopausal women who are more at risk of breast cancer due to age, weight or environmental factors, particularly if there is a family history of oestrogen receptive tumours.
Antonia Dean, Breast Cancer Nurse Specialist at charity Breast Cancer Care, says further investigation is needed: ''While this study is interesting, it does not prove any definitive link between eating grapefruit and breast cancer risk nor isolate it from the potential effects of other food groups or lifestyle factors."
If any immediate good can come of research, says Collins, it is to highlight the risk of polarised eating habits such as the Grapefruit Diet.
''Eating one particular food can upset your natural balance. That's why your 'five-a-day' should be five different varieties of fruit or vegetable. You want to get access to the whole plant chemical spectrum for their maximum health benefit.''