The human body needs to consistently balance the amount of food we consume with the amount of energy we expend. There are two hormones, leptin and ghrelin, that signal these needs to us. Ghrelin tells that we are low on energy and need to eat, whilst leptin signals that we’ve consumed enough.
In order to maintain a normal balanced weight, we need a consistent balance of these hormones. An imbalance can cause excess eating and, therefore, weight gain.
Dr. Eve Van Cauter of the University of Chicago asked individuals to participate in two studies. Both studies (5 nights each) are done under the same controlled conditions, with the exception of sleep opportunity. This means that food allowance and activity were identical and no caffeine was allowed.
In the first study, the participants were allowed up to 8.5 hours sleep whilst in the other, it was reduced to 5 hours. In each study, the participant’s desire to eat was monitored, as well as the levels of leptin and ghrelin.
The results showed that even though food intake and energy expended were the same, when the participants were deprived of sleep, their hunger pangs were significantly heightened within only a couple of days.
It was found that sleep deprivation had caused both an increase in leptin and a decrease in ghrelin, i.e. there was less leptin to tell them they’d had enough to eat, whilst at the same time there was an increase in ghrelin telling them to find more food.
In a slight twist, Dr Van Cauter ran similar studies, done under the same conditions with the exception that the participants had free access to food. It was found that when the participants were deprived of sleep, they consumed an extra 300 calories per day. If this was maintained for a month, that’s 9,000 calories which equates to over 1.2kg of fat (or 2.5lbs).
Interestingly, similar results are seen when sleep is reduced to just 6 hours over a ten day period.
It has also been shown (Van Cauter) that sleep deprived individuals have a preference for sweet, salty and carb rich foods – cravings for these foods rise by 30-40%.
It is no surprise that the rise in obesity has coincided with a decrease in sleep in industrialised society.