That midnight trip to the fridge might be doing double damage. Most people know by now that it's poor dietary form to eat right before bed, but the body's natural circadian rhythm and related rest cycles might also have more to do with weight gain than previously thought, according to a study published online today in the journal Obesity.

With more than a third of U.S. adults tipping the scales to obese levels, rooting out the many causes of our collective weight gain has proved to be a difficult undertaking.

"How or why a person gains weight is very complicated, but it clearly is not just calories in and calories out," Fred Turek, a co-author of the study and professor of neurobiology and physiology at Northwestern University's Weinberg College of Arts in Evanston, Ill., said in a prepared statement.

Researchers in his lab at Northwestern's Center for Sleep and Circadian Biology were interested in the observed weight gain in late-night shift workers. "Their schedules force them to eat at times that conflict with their natural body rhythms" as cued by daylight and other signals, Deanna Arble, lead study author and doctoral researcher in Turek's lab, said in a prepared statement.

To examine off-schedule eating, the research team divided lab mice into two groups: active-period eaters and rest-period eaters. The mice that were given unlimited access to high-fat food only during their normal rest periods increased in heft by 48 percent, whereas those given unlimited access to fatty food during their normal activity periods put on about 20 percent of bulk over their baseline. The next step will be to pinpoint the mechanisms behind this finding, the researchers note.

The link between the circadian rhythm and weight is not a new one. In 2007, researchers located Nocturnin, a gene that works in both the circadian clock and in controlling weight gain in fatty diets. And two studies published earlier this year in Science illuminated the relationship further, detailing the role of coenzyme NAD+ in the circadian cycle and the connections between circadian protein CLOCK and the metabolic gene SIRT1.

While many of the mechanisms remain mysterious, simply shifting snack time could help some trim down. "Better timing of meals, which would require a change in behavior, could be a critical element in slowing the ever-increasing incidence of obesity," Turek said.

Image courtesy of Wikimedia Commons/Pharos