Marijuana-induced munchies have provided us with our fair share of laughs in movies like Cheech and Chong or Harold and Kumar. Being sleep-deprived can also bring on the munchies, minus the marijuana. We are not entirely sure why sacrificing sleep can make us crave sweet, fatty and energy-dense foods (aka junk food). But a new study published in the journal eLife shows that sleep loss influences food consumption by manipulating your sense of smell.

A ‘dope’ system for hunger regulation

Marijuana or cannabis contains chemical compounds called cannabinoids. These compounds can produce hallucinogenic effects, improve mood, ease pain and induce hunger. They do so by acting on a network of nerves that connect the brain to other organs.

Our body also has compounds that act on this neural network and produce effects similar to cannabis. These chemical messengers produced by our body are called endocannabinoids and the complex network they act on is called the endocannabinoid system. When the endocannabinoid system is turned on, it triggers food cravings.

But what does this have to do with sleep?

What do insomniacs eat?

Researchers from Northwestern University in Chicago wanted to determine if sleep deprivation influenced food intake by throwing the endocannabinoid system off-kilter. They recruited 25 healthy people to sleep for the recommended 8 hours or follow a sleep loss protocol with only 4 hours of sleep for a night.

In sleep-deprived individuals, levels of a cannabis-like molecule (an endocannabinoid) were 35% higher than in individuals who slept well. Remember that endocannabinoids are chemical messengers within the body that stimulate hunger. Therefore, researchers were curious whether sleep-deprived individuals ate more than those who slept adequately.

Both sleep-deprived and well-rested individuals were allowed to eat as much as they liked at a buffet. There were no differences in hunger levels between the two groups, or the total number of calories they consumed. However, sleep-deprived individuals opted for more energy-dense foods and derived a higher percentage of their calories from fats.

So, sleep deprivation did not make people more hungry, but made them crave fatty and high-energy snacks.

The sweet smell of insomnia

Food aromas play an important role in regulating food intake. Doesn’t the smell of fried food outside a fast food joint make you hungry? Food smells can stimulate appetite and our sense of smell gets sharper when we are hungry.

A previous study in mice showed that the endocannabinoid system is also involved in odor processing. In fact, hungry mice had a sharper sense of smell because activation of the endocannabinoid system ramped up activity in smell-processing regions of the brain. Is a similar mechanism at play in sleep-deprived humans?

To answer this question, the brains of sleep-deprived and well-rested individuals were scanned using functional MRI. Functional MRI is used to measure activity and connectivity between various brain regions. While in the scanner, participants got a whiff of food aromas and non-food smells.

Researchers measured brain activity in the piriform cortex – a pear-shaped region of the brain that interprets smells and is dotted with endocannabinoid receptors (that bind to endocannabinoid). They also explored how this pear-shaped brain region interacts with the insula. The insula is a region deep inside the brain that integrates information from various brain regions to estimate the body’s needs and guide food intake.

In people who did not get enough sleep, the odor decoding region had a stronger response to food aromas. Sleep deprivation also dampened communication between the odor decoding piriform cortex and the signal integrating insula. Thus, sleep loss enhances our ability to smell food, but blocks brain pathways that convey information about hunger satiety. In short, insufficient sleep makes us gravitate towards junk foods by meddling with the smell processing and hunger control mechanisms in our brain.

An evolutionary perspective

Our sense of taste and smell are the result of millions of years of evolution. They enabled our food foraging ancestors to find nutrient-dense and energy-rich sources of food. Such foods were rare in our prehistoric environs. With the threat of predators looming overhead, our ancestors had to be able to find these precious foods quickly.

“We evolved in an environment that is very different from that we currently inhabit…A major problem is that these hardwired adaptive systems are less able to cope with a situation where such ‘advantageous’ foods are no longer rare, where novel macronutrient combinations are available that did not exist in prehistory, and where food is continuously available.” – B.L. Heitmann et al., Obesity Reviews, 2012.

But our modern world is a cornucopia of energy-dense sugary and fatty foods. In this age of abundance, our evolutionary adaptations are turning into a bane.

So how do we save us from ourselves? Here are a few habits you may consider adopting:

1. Get 7 – 9 hours of sleep every night. Avoiding blue screens, caffeine and alcohol a few hours before bedtime to help yourself fall asleep more easily and sleep more deeply. Following a sleep routine that includes light stretches and relaxation may also help ensure a good night’s sleep.

2. Eat with the sun. Eating during the 8 – 10 hour window when the sun is out ensures that your digestive system is not working too hard, too close to your bedtime. This form of intermittent fasting, also called time-restricted eating, also has health and longevity benefits.