It has been repeatedly proven that poor sleep promotes weight gain. In humans, acute sleep disturbances can lead to increased appetite and insulin resistance. People who sleep less than six hours a night chronically also have a higher risk of obesity and type 2 diabetes. However, it is not clear how sleep and diet are related. According to a new study published in PLOS Biology, it is indeed obesity that can lead to poor sleep.
“We wanted to know what sleep really does. Sleep deprivation and other chronic diseases like diabetes are related, but this is just a link. It is not clear whether not getting enough sleep is the cause of the tendency to become overweight or perhaps obesity is the cause of the tendency of not getting enough sleep”, says Alexander van der Linden, associate professor of biology at the University of Nevada and co-author of the study.
To investigate the relationship between metabolism and sleep, he and his colleagues worked with microscopic worms called Caenorhabditis elegans (C. elegans) and modified a gene called KIN-29 in them to turn off a neuron that controls sleep. As a result, the worms have lost their ability to sleep. Researchers then discovered that the level of adenosine triphosphate (ATP), the body’s energy exchange currency, had significantly decreased in insomniac worms.
“This suggests that sleep is an attempt to save energy; it doesn’t actually cause energy loss,” says co-author of the study David Raizen, associate professor of neurology and a member of the Chronobiology and Sleep Institute in Penn.
Releasing the fat reserves could promote sleep
By neutralizing KIN-29 to produce worms with insomnia, the mutant worms have accumulated excess fat, similar to that found in human obesity. The release of fat reserves is therefore a mechanism that could promote sleep, researchers argue. Mutant worms may have become sleep-deprived because they cannot release fat. To test this hypothesis, the researchers manipulated the worms again, this time with an enzyme that released their fat. As a result of the fat release the worms were able go back to sleep.
According to the researchers, these results could partly explain why people who are obese tend to have insomnia. “There could be a signaling problem between the fat reserves and the brain cells that control sleep”, explains Raizen.
A reliable model of mammalian sleep
“Our results indicate that if you fast for a day, we assume that you might fall asleep because your energy reserves will be exhausted. – he says. In terms of sleep, there is a general feeling that sleep is a matter for the brain or nerve cells, and our work suggests that this is not necessarily true.
While these worm discoveries cannot be directly transferred to humans, C. elegance provides a reliable model for mammalian sleep, according to the scientists. In fact, like all other animals that have a nervous system, they need sleep. But unlike humans, who have complex neural circuits, C. elegance has only 302 neurons – including the sleep regulator.
So while there is still much to discover about sleep, this discovery may speed up our understanding of one of its basic functions and perhaps eventually help to treat its disorder, scientists hope.
Chronic sleep deprivation is rife in our modern societies
In general, scientists tend to see weight gain as a possible consequence of chronic sleep deprivation. For example, a 2016 English study published in the European Journal of Clinical Nutrition found that people who slept less ate an average of 385 calories more within a 24 hours after a bad night’s sleep.
“Our results suggest that sleep is the third potential factor for weight gain, after diet and exercise,” the researchers said. Reducing sleep time is one of the most fundamental and potentially easiest factors to correct in order to lower the health risks. Chronic sleep deprivation is widespread in our modern societies, and further research is needed to assess its long-term effects on obesity and the extent to which sleep can be a preventive factor.