Lack of sleep can make you fat, scientists claim They were allowed to sleep from 11pm to 7.30am during one testing period and from 1am until 5.30am during the other. During waking hours, the subjects ate a controlled number of calories based on their height and weight. After the second night of each sleep condition, the researchers took blood samples from the subjects at one-hour intervals for 24 hours. They analysed the samples for 2-AG, a component of the endocannabinoid system. This system plays an important role in the signalling of rewarding events and enjoyment of eating, similar to the cannabinoids in marijuana. Levels of 2-AG levels were the lowest halfway through sleep and the highest in the early afternoon, "when the pleasurable properties of food would be most beneficial," Dr Hanlon said. She reported that the afternoon peak of 2-AG was even higher when the participants had partial sleep restriction than when they had normal sleep. Dr Hanlon said: "These findings are highly relevant to millions of individuals who are at an increased risk of obesity and its health consequences because of chronic short sleep or sleep disruption."