Poor sleep causes us to crave junk food, according to a study by the University of Chicago.

Sleep deprivation increases hormones called endocannabinoids, which are associated with the “munchies”. They make eating more enjoyable, but they also increase our desire for specific types of foods such as cookies, cakes and chips.

Professor Thorsten Kahnt, who heads the study at Northwestern University in Chicago, said, “It might be worth taking a detour to avoid your local doughnut shop next time you catch a 6am flight.”

The study showed that “When you're sleep deprived these brain areas may not be getting enough information. You're overcompensating by choosing food with a richer energy signal.

Professor Kahnt told the Sun: "We put all this together and asked if changes in food intake after sleep deprivation are related to how the brain responds to food odours - and whether this is due to changes in endocannabinoids."

In experiments, 29 men and women between the ages of 18 and 40 were split into two groups - one got a normal night's sleep and then, four weeks later, only four hours. On the day after each test, they were given a controlled menu for breakfast, lunch and dinner, and then also offered a buffet with snacks. Scientists measure how much and what participants eat.

Professor Kahnt said: "We found participants changed their food choices. After being sleep deprived, they ate food with higher energy density like doughnuts, chocolate chip cookies and potato chips." 

The researchers hope the results will help solve the problem of obesity.