People woken at night by insatiable hunger may have their genes to blame, research suggests.
Night-eating syndrome may appear when the genes that synchronise eating patterns with sleep are faulty, research on mice concluded.
This alters meal times, leading to over-eating and weight gain.
About 1-2% of people have the condition. Signs include waking in the night and being unable to go back to sleep without eating.
The syndrome has recently been classified as an eating disorder, but the cause is unknown.
The food consumed is often unhealthy and high in calories, leading to weight gain and sometimes obesity.
The study, published in Cell Reports, looked at mice bred with a human version of a body-clock gene in place of the mouse one.
When the gene was silenced, the mice ate much earlier than normal ones, when they should have been asleep.
Mutations in a related body-clock gene - implicated in sleep disorders - led to the mice sleeping more.
The researchers think the genes work together to keep eating and sleeping synchronised.
A fault in either gene causes disruption in sleeping and eating patterns.
"For a long time, people discounted night-eating syndrome as not real," said lead researcher Satchidananda Panda, of the Salk Institute in La Jolla, US.
"It opens up a whole lot of future questions about how these cycles are regulated."， 英语短文