In a study, billed as 'the first to examine whether too much sitting alters our perception of hunger', the researchers monitored the appetite of young men and women asked to be active or inactive for a day at a time.
During active days, the volunteers spent 12 hours on the go.
Although they did not take part in any sports, they walked and did housework and could only sit down for 10 minutes in every hour, reports the Daily Telegraph.
During the 'lazy' days, they spent their time sitting down, watching videos and playing on computers.
If they wanted to go somewhere, they were pushed there in a wheelchair.
During the whole process, the scientists counted the calories eaten by the men and women, who were all fit and lean.
The next morning, they were given breakfast and asked how hungry they were before and after the meal.
Surprisingly, the couch potatoes felt the hungriest, an American Physiological Society conference heard.
They felt up to 17 per cent hungrier before eating and did not feel as full as the others afterwards.
The researchers said that although the results were preliminary, they suggested that exercise blunts appetite, while sitting still boosts it.
In a warning to couch potatoes everywhere, Dr Barry Braun, of the University of Massachusetts, said: "In addition to reducing energy output, sitting for long periods may increase the perception of hunger.
If you are sitting on the couch or at your desk, not only are you not burning calories, it may cause you to want more of them."