Writing in the British Medical Journal, the Berlin medical researchers said consumption of more than 5 grams of sorbitol could cause severe gas and cramps, and that intake of more than 20 grams could cause diarrhoea resulting in excessive weight loss and dangerous dehydration.

Doctors at Berlin’s famed Charite University Hospital outlined the case histories of two patients who had been admitted with inexplicably severe gastro-intestinal cramping and diarrhoea.

A 21-year-old woman had diarrhoea and abdominal pain for eight months, and lost 11 kilogrammes (24 pounds), the British Medical Journal report says. A 46-year-old man lost twice as much in over a year. After no cause was found they were asked about diet. Both heavily consumed sorbitol.

The woman ate up to 20 grams of sorbitol daily, the man 30 grams. The source was sugarless chewing gum. The man also ate sugar-free sweets which contained sorbitol.

In both cases, the patients’ symptoms immediately went away when doctors ordered them to stop chewing sugarless gum and sweets containing sorbitol.

"The investigation of weight loss should include detailed dietary history with regard to sorbitol," wrote Juergen Bauditz, who led the study at the hospital’s Department of Gastroenterology .

Sorbitol has long been known to act as a laxative, and products containing sorbitol always carry small-print warnings that excessive consumption can result in "laxative effects."

But the food industry insists that sorbitol is a safe product and packs carried warnings about excessive consumption.

Wrigley’s issued a statement saying that up to 40 grams of sorbitol could be consumed safely.

But the Berlin researchers said that some persons may be sensitive to far lower amounts.

"Our cases demonstrate that sorbitol consumption can cause not only chronic diarrhoea and functional bowel complaints but also considerable unintended weight loss (about 20 percent of usual body weight)," the researchers wrote.