It's logical to think that an overweight employee incurs greater health care costs than a thin employee. New research from the University of Michigan actually calculates the cost -- and shows that it rises like a soufflé as workers gain weight. The study looks at small companies in Jackson, Mich., where many employers have recently cut benefits. Early findings indicate that overweight and obese workers cost companies as much as $1,500 more annually to insure. Their outpatient and inpatient expenses are higher, as are prescription drug costs. (Costs are also high for underweight workers.)What's a company to do? Some hold weight-loss contests. Helen Darling of the Washington Business Group on Health suggests putting some healthy snacks in vending machines and posters by the elevators that urge employees to "try the stairs." And the government should help, adds study director Dee Edington, by offering tax credits to companies that offer health and wellness programs.