The editors claim users can work off 96 calories per hour by surfing the site.

CNN: Site Seer: Get fit on the Net

Casually work off those calories while moseying down Wharf St and let the eclectic mix of live music and lounge chatter wash over you.

BBC: Art appreciation and more in Portland, Maine

While Americans expend fewer calories at work, they spend more time in cars -- almost twice as much as in the 1970s.

CNN: Why we're getting fatter -- and what to do about it

So retro foods -- which are often minimally processed, easy to eat, and so low in calories and fat they're almost guaranteed to work -- appeal to them, Lempert adds.

CNN: Retro diet tricks that work

Further work may may clarify whether the relationship is as complicated as short sleep disrupting the body's ability to process calories, or as simple as people who report very short sleep also under reporting the amount they eat.

CNN: Does your diet influence how well you sleep?

Once you know how many calories you burn each day, the answer to how many additional calories you should eat has not really been established and depends to a great extent on how hard you work in the gym.

CNN: How should I eat to build muscle mass?