Science wakes up to the 'duvet diet'
RICHARD GRAY
HEALTH CORRESPONDENT (rgray@scotlandonsunday.com)
TIRED of Atkins? Fed up with GI? Bored with Detox? Then here's the ultimate in painless dieting: just stay in bed.
New research suggests a link between getting extra sleep and a reduction in appetite. Just one hour's slumber a day could result in losing 10lbs a year, according to scientists.
Vivienne Parry, a former host of BBC's Tomorrow's World and author of a new book on hormones, told the Edinburgh International Science Festival that new research showed hormones that control appetite can be disrupted if we get too little sleep and fool the brain into thinking more food is needed.
Parry believes long working hours and late nights are causing many families to cut back on sleep, fuelling the country's obesity crisis.
The theory conflicts with the traditional assumption that sleeping for long periods is "lazy" and makes the sleeper more prone to obesity.
Parry claims the "duvet diet" could cut around 100 calories out of your food intake every day simply by sleeping for an extra hour each night.
Kept up for a year, that could equate to a weight loss of around 10lbs.
"Over the past 30 years there has been a huge rise in obesity and a huge fall in the number of hours people sleep at night," said Parry.
"The body is a fantastically scheduled machine. When you are awake, the body thinks it needs fuel as it must be daytime and you are more active during the day.
"It increases the amount of ghrelin, a stomach hormone that drives appetite, and also decreases the amount of leptin, which makes your body believe it is starving.
"But the less you sleep, then the levels of the hormones in the body that regulate appetite change. This tricks the body into thinking it needs more food when you are awake for longer when in fact you have probably eaten enough."
Parry, author of The Truth About Hormones, points to research carried out at the University of Bristol by Dr Shahrad Taheri, one of the few scientists in the UK examining the link between weight and sleep.
His research has shown that reducing levels of sleep from 10 hours to five hours a night for two days causes an increase in the body mass index of volunteers by around 4%.
Blood samples from the 1,000 participants also revealed dramatic changes in the levels of the appetite-regulating hormones when they were deprived of sleep.
They noticed a 15% increase in ghrelin, which is released by the stomach to signal hunger, and a 15% decrease in leptin, which is released by fat cells to signal the state of fat stores.
Another recent study of 400 children aged between five and 10 years old in the US showed that those who slept for around 11 hours a night had a 40% increased risk of becoming overweight or obese than those who slept around 13 hours.
Taheri believes that the amount of sleep an individual needs to encourage weight-loss will vary from person to person. He is now attempting to unravel whether short power naps or longer deep sleep is best.
He said: "When people don't sleep they tend to be too tired to do enough physical exercise. This combines with the effect on hormones to produce quite a dramatic change in the obesity levels.
"We found that sleeping eight hours compared with five hours produced the equivalent hormone response we would expect to see in someone who has been on a 1,000 calorie-a-day diet for three months.
"In a normal diet you would expect to see the hormones slowly reset themselves, but simply by getting more sleep this happened overnight.
"In obese people this can be quite significant as it can mean the difference between suffering from diabetes and not."
Health experts claim longer working hours and heavier traffic is to blame for the low levels of sleep achieved by most of the population. Just 19% enjoy the eight hours a night recommended for maximum refreshment.
Doctors warn that sleep deprivation can increase the risk of heart problems, impaired memory and poor concentration.
Professor Jim Horne, from the Sleep Research Centre in Loughborough, said: "There is no evidence that we all need eight hours sleep a night - it depends on the individual.
"Everyone needs to work out what is right for them and if they are feeling sleepy in the afternoon then they probably have not had enough."
But Professor Mike Lean, an obesity expert at Glasgow University, said he did not think sleep played a significant role in weight gain. "The old theory was the more a person slept, the fewer calories they used up so they stored them instead and this caused them to get fat.
"Now the belief is that because people sleep less they are feeling less full due to the mechanism of hormones such as leptin."
He added: "It is fairly complex area and there are a number of factors that influence weight control."
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