People who sleep five hours or less a night are more likely to snack after dinner and gain more weight than those who get a full night’s rest, a new study has found.
Staying awake burns more energy than sleeping but after-dinner snacks can quickly distort the energy balance, the study found, with researchers recording weight gain in people who under slept five days in a row.
The University of Colorado researchers, whose findings were published in the journal PNAS, examined hormonal and weight changes in 16 people over two weeks who were allowed to sleep only five hours a night.
The researchers also analysed the subjects under normal conditions, where they were allowed to sleep up to nine hours a night. The participants were given access to sunlight and opportunity to exercise.
“We found that insufficient sleep increased total daily energy expenditure by [approximately] 5%; however, energy intake – especially at night after dinner – was in excess of energy needed to maintain energy balance,” the researchers wrote in their paper.
“Our findings suggest that increased food intake during insufficient sleep is a physiological adaptation to provide energy needed to sustain additional wakefulness; yet when food is easily accessible, intake surpasses that needed.”
The study subjects overate despite the release of hormones signalling the body does not need extra energy from food, the researchers said.
The participants’ food intake fell when they were allowed to sleep up to nine hours overnight and their weight dropped correspondingly.
Co-author of the study, Associate Professor Kenneth P. Wright Jr from the University of Colorado’s Department of Integrative Physiology, said there were no insomniacs among his study subjects.
“We did not study patients with insomnia and our findings may not directly translate to the insomnia patient population,” he said.
Dr Siobhan Banks, Senior Research Fellow, Centre for Sleep Research at the University of South Australia, said it was “a beautifully controlled study.”
“They didn’t just examine the hormonal consequences of sleep loss or what was eaten but also the energy expenditure,” said Dr Banks, who was not involved in the study.
The researchers tried to be realistic by making sure the study participants exercised a little and were exposed normal amounts of daytime light, she said.
“A lot of studies done previously were quite artificial because the tests they used didn’t allow for normal consumption of food,” she said.
People who regularly get insufficient sleep, such as shift workers or insomniacs, should try to limit food intake at night, said Dr Banks.
“There’s a difference between fancying something for the psychological comfort and really being hungry. That’s something we always need to ask ourselves before a meal or snack. Am I really hungry?” she said.
“If you really are hungry, go for a small, protein-based snack.”
Gaining weight might increase the risk for other comorbidities that might complicate insomnia, said Dr Banks.
“Being overweight might make you feel more anxious or depressed which could exacerbate insomnia and lead to a vicious cycle of weight gain and difficulty sleeping.”
Professor Leon Lack, a sleep expert in the School of Psychology at Flinders University, said it was a well-designed study.
“It reinforces earlier studies but the careful control was able to isolate the weight gain to greater calorie intake than expenditure in the sleep restricted group. So, an imposed reduction in sleep by about three hours per night can lead to weight gain with all the possible increased health risks associated with that,” said Professor Lack, who was not involved in the study.
“One question that now needs to be investigated is what would happen in a normal life situation if reduced sleep occurred as a result of increasing life demands, such as additional tasks, deadlines and stress?” he said.
“This might result in an increased activity level and metabolic rate that balances increased food intake. This could be investigated in a longitudinal study where individuals encounter changing life demands (for example, high stress work alternating with holidays) in which both sleep length, activity levels, and probably metabolic rate all vary to mutually compensate each other.”
Insomniacs, who are distressed by their poor sleep and often in stressful conditions don’t seem to be overweight on average, despite their reduced amount of sleep, said Professor Lack.
“I am a bit concerned that the results of this type of study may be interpreted too broadly and increase the anxiety of insomniacs about their shorter sleep, thus exacerbating their insomnia.”