You'd better believe it, says Ellen Langer, PhD, a Harvard University psychologist. She told 44 hotel maids their job was a good workout. A month later, they'd shed about a kilo.

They say they didn't work any harder, but their mind-set had changed: They believed cleaning could help them shape up, and somehow it did. "If you put the mind in a healthy place, the body will be in a healthy place," says Langer.

But Cedric Bryant, PhD, of the American Council on Exercise, isn't so sure. "I wonder if changing their perception had an impact on their behaviour outside work. Did they think, Jeez, I'm becoming healthy while I work -- now I should eat better? The study didn't measure that." In any case, everyday activities do add up.