New Delhi, March 2 -- Otto's, a restaurant in London, is known for serving generous portions of indulgent dishes: lobster, canard a la presse and burgers heaped with caviar and foie gras. But when a regular customer informed Otto Tepasse, the owner, that he was taking weight-loss medication and would be dining out less frequently, Mr Tepasse decided to adapt. The restaurant launched a menu of "exquisite bites" such as pan-fried veal. "You get all the luxury," says Mr Tepasse, "but in small quantities."

Other restaurants are downsizing their dishes, too. At the Fat Duck (pictured), a three-Michelin-starred restaurant in Berkshire, Heston Blumenthal offers a "Mindful Experience" option. ("Sometimes less really is more," the menu claims.) T...