While many experts believe that weight gain and obesity are caused chiefly by too much eating and too little physical activity, additional factors may help explain the dramatic increase in obesity worldwide.
Geneticists Molly Bray and Martin Young at the Children's Nutrition Research Center (CNRC), Houston, Texas, are exploring human circadian rhythms and their effect on obesity. The CNRC is operated by Baylor College of Medicine in cooperation with Texas Childrens Hospital and the Agricultural Research Service (ARS), the U.S. Department of Agricultures chief scientific research agency.
Circadian rhythms include sleep-wake cycles controlled by an inner biological "clock" on roughly a 24-hour schedule. Biological rhythms, such as the sleep-wake cycle, are central to all aspects of life. Because of this circadian clock, sleepiness is not solely the result of passing time. It's influenced by the length of time since a person previously awoke from sufficient sleep and the internal circadian rhythm, so sleep and wakefulness can occur at different times of the day or night.
Recent reports suggest that disruptions in sleep patterns in children may be linked to todays round-the-clock lifestyle, caused in part by increased sedentary entertainment options like video games, television and the Internet. Such nonphysical activities have been associated with increased body fat and altered metabolism.
Abnormal sleep/wake patterns may change circadian clocks that normally allow cells to anticipate variations in the outside environment, such as changing levels of nutrients (glucose, fatty acids and triglycerides) and hormones such as insulin.
Young focuses on the circadian clock's effects within heart muscle cells and has published several papers on the topic, including a recent review in the September issue of Sleep Medicine. Bray has extended the research focus of Youngs work into the area of obesity, and they published their initial work in Obesity Reviews earlier this year.
Bray and Young are both optimistic that identifying the role of the circadian clock mechanism within fat cells may lead to improved understanding of the increasing obesity problem and the timing of obesity therapies.