According to behavioral neuroscientist, Erin Hanion, who is studying connection between behavior and brain systems at Chicago University, when people are sleep deprived they tend to crave junk food which could be sweets or starchy items. This behavior is linked to our evolution history when humans foraged dirt for starchy tubers, sweet berries and other fatty foods. In other words lack of sleep triggers yearning for sweet, rich and fatty foods. Hanion explained that during evolution eating high carb diet rich in fatty components was special as it was difficult to have those items every-time.
During times of famines and feasts too people would natural gravitate towards meals with plenty of carbs or sweet as brains are attuned to eating rich food. Only in last few years that humans have been able to acquire food when desired and have easy accessibility to food rich in carbs and saturated fat. But our brain has not evolved as quickly as our food choices as two hormones namely leptin and ghrelin control our eating urges. While Leptin helps in weight loss as it suppresses appetite, Ghrelin stands for weight gain as it increases hunger and leads to increase in weight.
Research shows that when an individual is sleep deprived then level of ghrelin spikes and leptin level falls drastically. But the question of why we crave only sweet and fatty food when sleep deprived is related to endocannabinoid system of the body. Its function is to keep our body is in equilibrium and regulate issues like sleep, appetite, inflammation, pain and others. There are several cannabinoid receptors in all vertebrates and a few invertebrates too one of which is the sea squirt that lived 600 million years ago.
Researchers believe that these endocannabinold system increases our cravings for fatty and sugary foods. Hanlon’s study published in 2016 showed that people who had higher concentration of endocannabinoids 2-AG during the afternoon were sleep deprived and had a tough time controlling their urge for high carb snacks.