A sleepless night can easily find a person craving high-energy junk food like doughnuts and pizza the next day. Now a new study has figured out just what is going on in the brain to drive this.
It is a common observation that people who do not get enough sleep, often start to favour energy-dense sweet and fatty foods which are not so good for the risk of weight gain. Just why there is a connection between sleep deprivation and food preference has mystified scientists. One theory is that it could be because of a change in endocannabinoid production.
Your brain on junk food
Endocannabinoids are neurotransmitters that act in the brain and the peripheral nervous system and have wide-reaching regulatory functions on memory, sleep and the immune system. Of greatest interest though is the effect of endocannabinoids on appetite and energy balance metabolism.
Endocannabinoids can change how the brain responds to smell with this sense tightly linked to how and what a person chooses to eat. Recent experiments show that in rodents, endocannabinoids enhance food intake by influencing the activity of the brain areas that process odours.
So what happens to endocannabinoid activity, smell and food preference in sleep-deprived humans? To answer this, a research team from the United States recruited 29 healthy men and women aged between 18 and 40 to take part in a sleep study. In a sleep laboratory, one group were given a normal night’s sleep and then 4 weeks later were only allowed 4 hours sleep. The second group had the sleep experience reversed with the sleep deprivation first followed by a normal night’s sleep 4 weeks later.
The day after each sleep session, volunteers were served controlled menus for a full day of meals as well as a buffet of snacks. What and how much they ate was closely monitored.
Food choices were very different after each of the sleep conditions. With sleep deprivation, more high-energy food options like doughnuts and chips were eaten. Blood levels of endocannabinoids were also higher after sleep deprivation and this increase was related to changes in food choices.
To round out the experiment, people also underwent a functional MRI scan before the buffet to look at brain region activation. Food smells were wafted to the participants while being scanned. They then were presented with several different food and non-food odours. For sleep-deprived subjects, activity in one part of the brain called the piriform cortex differed the most between food and non-food odours.
The piriform cortex communicates with a part of the brain called the insular cortex and in sleep-deprived subjects, the connection between the two regions was impaired. This is important because the insula regulates food intake related to smell, taste and how much food is in the stomach. So, sleep deprivation could be a marker for lack of stimulation of these brain regions which leads to a desensitised smell response or faulty energy balance signalling.
What it all means
Sleep deprivation is never a good thing and now science shows how it can change the brain to make it more tuned to enticing food smells from high-energy junk food. So apart from getting more sleep, it is worth paying attention to the faulty signals that the brain may be sending for highly desirable food and keeping some distance from the enticing smells.