Scientists are to give new advice on how to win the battle against the bulge: stop counting calories and count sheep instead. At a key international conference on Sunday, researchers will seek to highlight that a good night’s sleep is as important a factor as any other in ensuring people control their weight and waistlines.

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Their research, which will be outlined at the European Congress of Endocrinology in Lisbon, will emphasise how disrupted sleep patterns – a common feature of modern living – can trigger changes in appetite, metabolism, motivation and physical activity, or even a combination of all these factors. This leads to disruption in people’s appetite and responses to food. The end result is weight gain. It is hoped that a breakthrough in public awareness of the issue could lead to significant health gains.

“Our studies suggest that sleep loss favours weight gain in humans. It is therefore fair to say that improving sleep could be a promising lifestyle intervention to reduce the risk of future weight gain,” said Christian Benedict, a neuroscientist at Uppsala University in Sweden, who is scheduled to speak at the Lisbon conference on Sunday.

Two-thirds of people in Europe are now considered to be overweight, while a quarter are reckoned to be obese and in real danger of damaging their health or of dying prematurely. Lack of exercise is clearly involved in this obesity epidemic, as is the increased availability of cheap processed food and sugary drinks. But sleep is also a factor, says Benedict, particularly in the 24/7 culture of the modern world, where more people are reporting problems getting quality sleep – and where studies have increasingly pointed to a higher correlation between sleep deprivation and weight gain.

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In one experiment carried out by the Uppsala team, a group of 14 male students were put through a series of sleep experiences ranging from normal sleep to curtailed sleep and to no sleep at all over several days. The students were then measured for changes in how much they ate, their blood sugar and hormone levels and in their metabolic rate. The results were striking.

Even a single night of missed sleep was found to slow a person’s metabolism the next day, reducing energy expenditure for tasks such as breathing and digestion by between 5% and 20%. The students also had higher levels of blood sugar, appetite-regulating hormones such as ghrelin, and stress hormones such as cortisol after sleep disruption. The sleep loss did not, however, boost the amount of food consumed during the day.

“Our findings show that one night of sleep deprivation acutely reduces energy expenditure in healthy men, which suggests sleep contributes to the acute regulation of daytime energy expenditure in humans,” said Benedict. He has also found healthy but sleep-deprived people prefer larger food portions, seek more calories, exhibit signs of increased food-related impulsivity, experience more pleasure from food, and expend less energy than control groups. Part of the problem stems from the fact that sleep loss shifts the hormonal balance from those that promote fullness (satiety), such as GLP-1, to those that promote hunger, such as ghrelin. As a result, people think they are hungrier than they really are.

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Further work from Benedict’s team has also shown that acute sleep loss alters the balance of gut bacteria, which has been widely implicated as key for maintaining a healthy metabolism. The same study also found reduced sensitivity to insulin after sleep loss. Benedict’s group is now investigating longer-term effects and also whether extending sleep in habitual short sleepers can restore these alterations in appetite and energy metabolism.

“Since perturbed sleep is such a common feature of modern life, these studies show it is no surprise that metabolic disorders, such as obesity, are also on the rise,” Benedict will tell the Lisbon conference today.