"One message from our paper is, 'Don't raid the larder at night,' " said Garret FitzGerald, director of the Institute for Translational Medicine and Therapeutics at Penn's Perelman School of Medicine. Lead author Georgios Paschos is a research associate in the lab.
The behavior change in mice immediately reminded FitzGerald of human night-eating syndrome, a condition associated with obesity that was first described in 1955 by Penn obesity expert Albert Stunkard. About 1.5 percent of the population has it. FitzGerald's group is now working with the Penn center that treats night eaters, the Center for Weight and Eating Disorders, to set up a study of whether people with the condition share metabolic or genetic traits with the day-eating mice.
Previous research also has shown that night-shift workers and people with sleep disorders are more likely to be obese.
Even so, Gary D. Foster, director of Temple University's Center for Obesity Research and Education, doubts the mice results can be extrapolated to human obesity treatment. What he found intriguing was the power of fat cells to change the animals' metabolism.
"I think this confirms what people have talked about for the past few decades: that fat is metabolically active," Foster said. "It's not just an inert storage tissue. If you can get mice to gain weight consuming the same number of calories, that turns conventional wisdom upside down."
FitzGerald's new line of research, published this month in Nature Medicine, is just a taste of how thoroughly animal bodies are attuned to the daily rotation of the Earth, even at the cellular level.
