Sleeping for an extra hour each night may hold the key to losing all those unwanted pounds, researchers have said.
"More sleep could be the ideal way of stabilising weight or slimming," said neuro-scientist Karine Spiegel, of France's INSERM, a public organisation dedicated to biological, medical and public health research.
While poor eating habits and lack of exercise clearly play a role in the global rise of obesity, recent data indicates that lack of sleep may also be a factor, and one that is often under-estimated.
Around 30 surveys carried out on wide population samples in seven countries have underlined a link between lack of sleep and excess weight or obesity in both children and adults, Spiegel said.
The first of the studies, carried out in 1992 in France, highlighted the problem in children and teenagers. Spiegel said the increase in obesity in the US in the second half of the 20th century corresponded with a mounting decrease in sleep.
Two key hormones produced at night which help regulate appetite were at play, she said.
Grehlin makes people hungry, slows metabolism and decreases the body's ability to burn body fat, and leptin, a protein hormone produced by fatty tissue, regulates fat storage.
"We have shown that less sleep (two four-hour nights) caused an 18 percent loss of appetite-cutting leptin and a 28 percent increase of appetite-causing grehlin," she said.
Such hormonal changes made people hungry for foods heavy in fats and sugars such as chips, biscuits, cakes and peanuts, she added.
The sleep loss caused a 23 to 24 percent increase in hunger, Spiegel said, translating into an extra 350 to 500 kilocalories a day, "which for a young sedentary adult of normal weight could lead to a major amount of added weight."
It was unclear whether several years of sleep deprivation could lastingly harm the body's ability to restore a balance between the two hormones.
A study released in Washington in February showed children lacking shut-eye faced a greater risk of becoming obese than kids who got a good night's sleep.
Each extra hour of sleep cuts a child's risk of becoming overweight or obese by nine percent, according to an analysis of epidemiological studies by researchers from Johns Hopkins Bloomberg School of Public Health.
By contrast, children who got the least sleep had a 92 percent higher chance of being overweight or obese than children who slept enough, said the study published in the journal Obesity.
"Our analysis of the data shows a clear association between sleep duration and the risk for overweight or obesity in children. The risk declined with more sleep," said Youfa Wang, a senior author of the study.
"Desirable sleep behavior may be an important low cost means for preventing childhood obesity and should be considered in future intervention studies," Wang said in a news release.
The researchers reviewed 17 published studies on sleep duration and childhood obesity.
Some research recommends that children under five years old sleep 11 hours or more a day, while children age five to 10 should get 10 or more hours of sleep, and children older than 10 should sleep at least nine hours.