Regular visits to a health club in the online virtual world Second Life appear to help shed the pounds in real life, say exercise scientists.
Participants in two 12-week weight loss programmes - one real, and one online - lost similar amounts of weight.
Indiana University researchers told a conference that confidence and motivation built in the virtual gym continued in normal life.
A UK psychologist said mixing online and real world support might work best.
Second Life, launched in 2003, allows individuals to create online personae and explore an online world, interacting with others.
Dr Jeanne Johnston, who led the study which was presented at the American College of Sports Medicine Conference in Denver, worked in partnership with a Second Life interactive weight loss community called Club One Island to devise a weight loss programme.
Overweight and obese people were recruited to take part in either this programme, or a similar programme delivered more conventionally in a face-to-face setting.
Both courses involved four hours a week at meetings either in Second Life or the real world.
Most of those taking part were women, with an average age of 46 in the Second Life programme, and 37 in the face-to-face group.
Side by side
Over the 12-week period, both groups achieved similar weight loss - losing 10 pounds on average.
However, when the groups were surveyed on whether their overall behaviour had changed, those using Second Life appeared to have made more changes towards healthy eating and physical activity, suggesting that they might fare better in the future.
Dr Johnston said: "It's counter-intuitive, the idea of being more active in a virtual world, but the activities that they do in a virtual world can carry over into the real world.
"The virtual world programme was at least as beneficial as the face-to-face programme, and in some ways, more effective.
"It has the potential to reach people who normally wouldn't go to a gym or join a programme because of limitations, such as time or discomfort with a fitness centre environment."
Dr Jeff Breckon, a researcher in exercise psychology at Sheffield Hallam University, said that there might be a role for virtual support of this type.
He said: "There is still evidence that one-to-one sessions can lead to successful outcomes.
"There may be a place for this, perhaps as an adjunct to these sessions, rather than a replacement."