Diets should supply sufficient essential nutrients, but crucially, should be low in calories. Diets that can prove harmful to health should never be chosen, she notes.

According to Lin Feng, nutritionist and secretary general of the public education department at the Beijing Nutrition Association, rapid weight loss is usually accompanied by a loss of body protein and lower vitality, but followed by a fast regaining of weight.

Meanwhile, the experts are all convinced that exercise is crucial to losing weight, irrspective of when the activity takes place.

The experts gave China Daily their thoughts on unhealthy weight-loss methods, such as:

The apple diet

Eat apples and nothing else, except water, for about three days. The method is based on claims that apples are good at "squeezing out" water and fat, and as well as providing enough nutrients to keep the body healthy.

Fan Zhihong comments: Apples have the image of a "healthy food", but in fact they are low in protein, B vitamins, calcium, iron and vitamin A.

The apple diet can only be used as a means of refreshing the digestive system for one or two days after greasy banquets. If adhered to for long periods, the apple diet will inevitably result in malnutrition and substantial loss of body protein. A serious loss of body protein is associated with a number of conditions, including poor digestion, irregular menstruation, anemia, edema, thinning or brittle hair, poor skin condition and general weakness.

A prolonged low-protein diet, such as this one, results in a heavy loss of body protein as well as water loss, which may manifest itself as a rapid reduction in weight. However, because the loss of body protein reduces the metabolic rate, when people resume their normal diet they will encounter a relentless rebound in weight.