Dieters in Hong Kong were Tuesday warned by government doctors against a craze for swallowing parasite worms as a means of losing weight.

The city's Department of Health has been alarmed to see websites offering products containing potentially fatal parasites as a means of weight control.

The products are thought to use Ascaris worms: giant intestinal roundworms which grow up to 40 centimetres in length in a host's intestine and lay up to 200,000 eggs a day.

A Department of Health spokesman warned that swallowing the parasites could cause abdominal pain and distention, vomiting, diarrhoea and malnutrition.

“Parasite infestation may also be fatal if serious complications such as intestinal, biliary tract or pancreatic duct obstruction arise,” the spokesman said. “The worms may even invade such organs as the lungs.

“The infestation can be treated with medication that kills the parasite. The worms may require surgical removal if there are obstructions.”

He urged people to consult doctors before dieting and said the only natural, healthy and effective means of weight loss was through dietary regulation and regular exercise.

Dieting is big business in Hong Kong where obesity levels have soared because of sedentary lifestyles, fast-food diets and long office hours in the city of 7 million.

Clinics and websites offer a bizarre variety of questionable short-cut weight loss methods including hot wraps, fat-dissolving injections and even using controlled fire to literally burn off fat.