New research suggests not getting enough sleep or even a single night of no sleep might lead to junk food cravings. The latest study pointed out that hormones do not entirely affect why people gain weight when they lack sleep, and the reason why the brain craves for junk food is due to the changes in the activity within and between regions of the brain which were involved in regulation and reward.
Jan Peters, a co-author of the research from the University of Cologne, said their research would help them understand the mechanism why sleep deprivation changes food valuation, the South China Morning Post reported.
The study, which was published in The Journal of Neuroscience, involved 32 healthy men aged between 19 and 33. All of them were given the same dinner - strawberry yogurt, apple, pasta, and veal. Then, the participants were either kept awake in the laboratory overnight with activities such as parlor games or were sent home to sleep wearing a sleep-tracking device.
The next morning, their hunger and appetite were rated, and 29 of them had their levels of blood sugar measured and hormones associated with appetite and stress. The participants also played a game, wherein 24 snacks were presented, like chocolate bars, and 24 inedible items, such as mugs or hats. They were asked to rate how much they would be willing to spend for the snacks or items on a scale of zero to three.
During a functional magnetic resonance imaging (fMRI) scan, the participants were asked to choose if they were willing to buy the item if it has a fixed price. This experiment allows researchers to understand the brain activity of each participant upon seeing images of food or other objects.
After a week, researchers repeat the experiment. Those who previously stayed all night were allowed to sleep, and vice versa. Results show that whether sleep-deprived or not, participants were all hungry during the morning and all of them had similar levels of blood sugars and most hormones.
But, those who don't get enough sleep were willing to pay more for food compared to those who were well-rested. Their blood also had a higher level of a substance known as des-acyl ghrelin, which is associated with "hunger" hormone ghrelin although its function is not yet clear.
The results of the fMRI revealed that sleep-deprived participants had greater activity in the brain's amygdala - where food rewards were processed - when food images were shown. There is also a strong link between the activity in the hypothalamus - involved in regulating consumption - and the price they would pay for food.
However, Peters said it's unclear what drives the changes in activity in the hypothalamus and amygdala. He said changes in other neurotransmitters, like dopamine, might be another candidate.
Meanwhile, Christian Benedict, a neuroscientist at Uppsala University in Sweden and was not involved in the research, welcomed the study. But, he said it still had some limitations, such as blood was not taken while participants were viewing images of food during the scanning task. The research didn't also compare the responses of participants to healthy food. He pointed out there are other factors affecting body weight, aside from sleep.
