Lack of sleep can be harmful as it can make participants feel less full after eating and metabolise the fat in food differently, says a study, adding to the mounting evidence that how harmful lack of sleep can be.

The study, published in the journal of Lipid Research, by Pennsylvania State University found that sleep disruption has been known to be have harmful effects on metabolism for some time. Orfeu Buxton, a professor at Penn State, added that long-term sleep restriction puts people at a higher risk of obesity and diabetes.

Kelly Ness, now a postdoctoral fellow at the University of Washington, ran the study when she was a graduate student in Buxton's lab. She and other researchers not only collected data but also spent time, "interacting with the subjects, playing games with them, talking with them -- helping to keep them awake and engaged and positive."

To find out how the uncomfortable schedule affected metabolism, the researchers gave participants a standardized high-fat dinner, a bowl of chili mac, after four nights of sleep restriction. "It was very palatable -- none of our subjects had trouble finishing it -- but very calorically dense," Ness said, adding that most participants felt less satisfied after eating the same rich meal while sleep deprived than, when they had eaten it well-rested.

Researchers then compared blood samples from the study participants. They found that sleep restriction affected the postprandial lipid response, leading to faster clearance of lipids from the blood after a meal. That could predispose people to put on weight. "The lipids weren't evaporating -- they were being stored," Buxton explained.

This study was highly controlled, which makes it an imperfect model for the real world, Ness said. It focused on healthy young people, who are usually at a lower risk of cardiovascular disease, and all of the participants were men. The researchers also wondered whether giving more recovery time would change the magnitude of recovery they observed. Nonetheless, according to Buxton, the study gives worthwhile insight into how we handle fat digestion.