Nov. 7 (HealthDay News) -- There's more bad news about a high-fat diet -- it disrupts the body's 24-hour internal (circadian) clock, which regulates sleeping, waking, eating, as well as the daily rhythms of many metabolic functions, U.S. researchers say.

A team from Northwestern University and Evanston Northwestern Healthcare (ENH) found that mice fed a high-fat diet gained weight and showed a sudden disruption in their circadian clock, eating extra calories when they should have been sleeping or resting.

The team also found that a high-fat diet caused changes in genes that encode the circadian clock in the brain and in peripheral tissues (such as fat), resulting in reduced expression of these genes.

The findings are published in the Nov. 7 issue of the journal Cell Metabolism.

"Our study was simple -- to determine if food itself can alter the clock," senior author Dr. Joe Bass, assistant professor of medicine and neurobiology and physiology at Northwestern and head of the division of endocrinology and metabolism at ENH, said in a prepared statement.

"The answer is, yes; alterations in feeding affect timing. We found that as an animal on a high-fat diet gains weight, it eats at the inappropriate time for its sleep/wake cycle -- all of the excess calories are consumed when the animal should be resting. For a human, that would be like raiding the refrigerator in the middle of the night and binging on junk food," Bass said.

SOURCE: Northwestern University, news release, Nov. 6, 2007