University of Manchester researchers have found out why people tend to nap after a heavy lunch. When people are hungry, there is a lack of glucose and nerve cells in the brain send signals that keep a person alert. However after lunch there is an influx of glucose, which prevents the nerve cells from sending alert signals and hence people feel droopy.
The University of Manchester team said that when the body needs fuel in form of glucose, it is alert, but when hunger is sated, the body's chemistry stops these alertness signals. The study, published in Neuron, could help scientists understand obesity and eating disorders.
In the study, the researchers looked at orexins, which are proteins produced by some nerve cells. In genetically engineered mice, the researchers found that glucose interferes with the behaviour of orexin neurons, thereby halting flow of signals.
"We have identified the pore in the membrane of orexin-producing cells that is responsible for the inhibiting effect of glucose. This previously unknown mechanism is so sensitive it can detect minute changes in glucose levels - the type that occurs between meals for example," said lead researcher Dr Denis Burdakov. "This may well provide an explanation for after-meal tiredness and why it is difficult to sleep when hungry."
Neil Stanley, director of sleep research at the Human Psychopharmacology Research Unit Medical Research Centre at the University of Surrey, called the study interesting. But he said, "We naturally have a dip in alertness around 2pm to 4pm that happens whether we eat lunch or not. We also do not get tired after eating breakfast because we are on the rising phase of our circadian rhythm."