A new study could explain why people burn fat more efficiently at certain times of day.

UC Irvine researchers have discovered that circadian rhythmsu00a0-- the internal body clocku00a0-- regulate fat metabolism. The find could lead to new pharmaceuticals for obesity, diabetes and energy-related illnesses.

Paolo Sassone-Corsi and his team found that a protein called PER2, which turns on and off PPAR-gamma's metabolic capabilities at regular intervals.

"What surprised us most, though, is that PER2 targets one specific amino acid on the surface of the PPAR-gamma molecule," Sassone-Corsi said.

"This kind of specificity is very rare in cell biology, which makes it exciting, because it presents us with a singular target for drug development."

Twenty-four-hour circadian rhythms regulate fundamental biological and physiological processes in almost all organisms. They anticipate environmental changes and adapt certain bodily functions to the appropriate time of day.

Disruption of these cycles can profoundly influence human health and has been linked to obesity, diabetes, insomnia, depression, heart disease and cancer.

The study appears this month in Cell Metabolism.