They took in 500 to 550 calories a day, using a meal replacement called Optifast plus vegetables for eight weeks.

But when sonograms were taken of patients using Optifast, researchers found that people who had gall stones developed them within just a few months of beginning the diet.

Existing examples include Musashi whey-protein supplements and PowerBar snacks for athletes; Sondalis and Nutren Glytrol liquid diets for diabetics; and Optifast powders and shakes for dieters.