BBC: Why we snooze after Sunday lunch

From BBC: Why we snooze after Sunday lunch:

University of Manchester researchers have discovered how the nerve cells in the brain that keep us alert become turned off after we eat.

Glucose - the sugar found in foods - stops these cells from producing signals to keep people awake.

The human body has an in-built mechanism which means that when the body needs fuel, the brain chemistry creates alertness.

But when that hunger is sated, the chemistry swings the other way.

Neil Stanley, director of sleep research at the Human Psychopharmacology Research Unit Medical Research Centre at the University of Surrey, said the work was interesting.

But he added: "There are many behavioural, circadian and societal factors that also determine whether we nap in the afternoon or not.

"The siesta is not only dependent on the intake of food.

"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."

And now we know.

(FYI: circadian rhythm
A daily cycle of biological activity based on a 24-hour period and influenced by regular variations in the environment, such as the alternation of night and day. Circadian rhythms include sleeping and waking in animals, flower closing and opening in angiosperms, and tissue growth and differentiation in fungi.)