I'm sure it's news to no one, but when you're tired it's really hard to resist binging on junk food. For me, the munchies usually start during a late work shift. When 5 PM hits I can often be found rummaging in my bag for coins and power walking to the fundraiser chocolates. Even that stale cake in the tearoom looks tempting.
Of course, it makes sense that we're eating more when we're awake for longer. But research suggests all those extra calories consumed when people "tired eat" far outweigh the energy you need to stay awake.
To put it simply: sleep deprived people tend to eat for pleasure, because they wantto, rather than because they need to. Average sleep times are falling, and with a growing body of evidence linking insufficient sleep to an increased risk of obesity, the tendency to binge eat when you're tired is a real health problem.
So why do we crave calorific snacks when we're sleep deprived? To answer this question, researchers at the University of Chicago looked to the endocannabinoid system. Yes that "cannabinoid" is a reference to cannabis. Endocannabinoids are a group of chemicals behave in a similar way to the active ingredients of marijuana (hence cannabis shout out in the name).
The endocannabinoid system is made up of two receptors: CB2, found on immune cells and tissues, and CB1, which is found mainly in the brain and spinal cord. It's the CB1 receptor that's responsible for the marijuana high. This receptor alsoplays a key role in stimulating reward-based or "hedonic" eating (i.e. inhaling Doritos at 2 AM).
The University of Chicago researchers conducted a small study, published in Sleep, which involved fourteen non-obese men and women aged 18-30 years who normally slept between 7.5–8.5 hours at night. Each subject was kept on a fixed diet (three identical meals per day) and randomly subjected to either four nights of normal sleep (8.5 hours) or restricted sleep (4.5 hours).
On the third day, each subject had hourly blood tests, checking the levels of the endocannabinoid 2-arachidonoylglycerol (2-AG) in their body. They were also asked questions about their hunger, appetite, and food intake. The next day, all the participants were treated to a buffet lunch and dinner. They could have unlimited snacks too. Basically, the dream.
Around four weeks later the participants were brought back and exposed to the opposite sleep condition. Basically, a nightmare that's also known as a "randomised crossover study."
What the researchers found was that for everyone in the study the levels of 2-AG in their blood peaked early afternoon and dropped to their lowest point overnight. However, the interesting thing was that the sleep-deprived people's peak 2-AG levels were around 33 percent higher. They also peaked later, around 2 PM versus midday for well-rested participants, and persisted until around 9 PM.
Basically, this isn't good. Particularly given recent data suggests a link between late eating and increased weight gain. But what these findings also suggest is that when people are sleep deprived, it may well be that their overactive endocannabinoid systems helping to drive their hunger. And when you think about how cannabis works in the brain, the study findings make sense.
When someone smokes weed, the THC binds to the CB1 receptors in their brain, which leads to a huge increase in appetite. Similarly, when the body is sleep deprived more 2-AG is produced, which binds to CB1 and makes us hungrier. This means that when we are tired, we get the biochemical equivalent of "getting the munchies."
So why have we evolved to get the munchies when we are sleep deprived? In a discussion with The Naked Scientist's Dr. Chris Smith, lead researcher Dr. Erin Hanlon admitted that they just don't know. One hypothesis proposed by the researchers is that it may have been protective at some point in our evolutionary history; our ancestors would have had to overeat when food was plentiful to store enough energy for times of famine. Now that food is readily available though this response has become maladaptive.
While certainly providing me with an insight into why I'm such a snacker, perhaps the most exciting impact of this study is the implication that endocannabinoids and their receptors could make good targets for anti-obesity drugs. The efficacy of such treatments have already been demonstrated in animal studies; a study published in the Journal of Clinical Investigation in 2003 showed that when the gene for CB1 is deleted in mice they eat less and become leaner.
However, given the potential complications associated with interrupting the endocannabinoid system (the CB1 blocker drug Rimonabant was withdrawn from the market because of major psychiatric side effects) a lot more research into this area is required. In the mean time, what I'm taking away from this study is that when I'm tired and hungry, maybe I should think twice about having that fifth biscuit…
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