In the fashionable dieting scene, fasts followed swiftly on the heels of the discredited restricted-food diets popularised by starlets. Fasts, we are told, give the digestion a spring clean, easing out toxins and removing all trace of junk food.

• There are several groups of people who should not undertake fasts. They are: pregnant or nursing mothers, diabetics, people with kidney or heart disorders or gastric ulcers, the underweight, elderly and anyone with a serious illness or taking medication. It is mandatory for anyone intending to undertake a fast for more than one day to consult their doctor first. Sponsored fasts have become a fashionable and perhaps apposite way of raising money for the Third World, but the above contraindications to fasting must be taken into account.

• Fasting is not productive in the long term as a method of losing weight even for the obese.

• The body does not need cleansing in this way. The digestive system, like the ear, for example, is designed to be self-cleaning and is highly organized.

Plus points

• Fasting may be useful in isolating food allergies, under supervision by your doctor or dietician: foods can be re-introduced one by one.

• If you are fit and healthy and have had a bout of overeating and overdrinking, fasting for one day may make you feel more alert and lively, and give you new determination to stick to a healthy diet. it is not advisable to make fasting part of a regular dietary plan. Recent claims that regular fasts prolong life have not been substantiated: eat a balanced, healthy diet rich in vitamins, minerals and trace elements as well as proteins, carbohydrates and fats.