Researchers from the Rockefeller and Columbia universities have uncovered new evidence that suggests people eat when they are not hungry because of previously-established eating habits that trigger the release of a special chemical released by the stomach into the brain.

They arrived at this conclusion by studying genetically engineered mice that lack a receptor for the chemical ghrelin as well as normal mice. The latter set were observed to forage for food at predicatble times, while those lacking receptors sought food later and less vigorously than the others.

"Circadian clocks allow animals to anticipate daily events rather than just react to them," said Dr Joseph LeSauter, the first author of the paper. "The cells that produce ghrelin have circadian clocks that presumably synchronize the anticipation of food with metabolic cycles."

Since these results show that the stomach can be pre-programmed to secret ghrelin, the researchers think regular mealtimes are an important aspect of avoiding obesity. "If you eat all the time, ghrelin secretion will not be well controlled," said another researcher, Dr Rae Silver. "It’s a good thing to eat meals at a regularly scheduled time of day."

Regular exercise and low-fat, balanced diets are also helpful in reducing obesity risk or losing weight.