Getting more sleep may be a handy way of shedding those extra pounds, new research suggests.
Experts found that adding an hour or so more of sleep per night shaved around 270 calories off people's daily diets – the equivalent of around three chocolate digestive biscuits.
Over three years, this could lead to a weight loss of 11.8 kilograms – simply by sleeping more, the researchers said.
A team from the University of Chicago wanted to look at how sleep interacts with obesity and so carried out a clinical trial with 80 adults.
Writing in the journal Jama Internal Medicine, they found that young, overweight adults who habitually slept fewer than 6.5 hours a night were able to add an extra 1.2 hours of sleep per night after undergoing counselling to improve their sleeping habits.
The results showed that getting more sleep reduced people's overall intake by an average of 270 calories per day, with some people consuming 500 fewer calories.
Dr Esra Tasali, from the University of Chicago's sleep centre, said the study had not intended to look at weight loss.
"But even within just two weeks, we have quantified evidence showing a decrease in caloric intake and a negative energy balance – caloric intake is less than calories burned," she said.
"If healthy sleep habits are maintained over longer duration this would lead to clinically important weight loss over time.
"Many people are working hard to find ways to decrease their caloric intake to lose weight – well, just by sleeping more, you may be able to reduce it substantially."
The study did not attempt to restrict people's diets. Instead, they slept in their own beds, tracked their sleep with wearable devices, and otherwise followed a normal lifestyle without any instructions on diet or exercise.
"Most other studies on this topic in labs are short-lived, for a couple of days, and food intake is measured by how much participants consume from an offered diet," said Dr Tasali.
"In our study, we only manipulated sleep, and had the participants eat whatever they wanted, with no food logging or anything else to track their nutrition by themselves."
Instead, to track how many calories people were consuming, a clinically-proven method was used that looked at changes in people's energy stores.
This urine-based test involves a person drinking water in which both the hydrogen and oxygen atoms have been replaced with less common, but naturally occurring, stable isotopes that are easy to trace.
Dr Tasali said that limiting the use of devices such as mobile phones before bedtime helped people get more sleep.
She added: "We saw that after just a single sleep counselling session, participants could change their bedtime habits enough to lead to an increase in sleep duration.
"We simply coached each individual on good sleep hygiene, and discussed their own personal sleep environments, providing tailored advice on changes they could make to improve their sleep duration."
