Blame your NOSE for craving pizza and doughnuts when sleep deprived

How your NOSE makes you crave pizza when you’re tired ‘because it causes a heightened sense of smell and makes the brain want to eat junk food’

  • Sense of smell is tightly linked to our taste and food choices
  • A study suggests food smells stronger to people who are lacking sleep
  • However, the information is not correctly communicated in the brain
  • This leads to overcompensation of food intake, scientists said 

Your nose may be to blame for craving pizza, fries or doughnuts when you’re tired, scientists say.

Researchers have now discovered sleep-deprivation dramatically heightens your perceived sense of smell. 

However, this information is not correctly relayed to the brain, causing you to seek junk foods to feel satisfied.

Northwestern University experts made the discovery after forcing almost 30 people to have just four hours of sleep.

Your nose may be to blame for junk food cravings when you’re deprived of sleep 

The next morning, volunteers were offered breakfast, lunch and dinner alongside a buffet of unlimited snacks such as crisps, cookies and hash browns.

All of the participants took part in the same experiment after a normal night’s sleep, either in the run-up to or weeks after.

Scientists measured how much and what they ate to see how their choices differed depending on how tired they were. 

The scientists looked into why the communication chain was being disrupted by focusing on the endocannabinoid system in the body. 

This system is a web of molecules, which, although are still being researched, are believed to play a role in processes such as appetite, pain-sensation, mood, fertility and memory. 

Studies on rodents found endocannabinoids enhance food intake by influencing the part of the brain that process smells.

Some work suggests that endocannabinoids may directly change how neurons work in the paths between the nose and brain.

Therefore, the scientists at Northwestern University took participants’ blood to look at which endocannabinoid molecules were present.

They found levels of a molecule called 2OG were elevated after the night of sleep deprivation. 

And when sleep-deprived people were given the choice to eat whatever they wanted at the buffet, those with greater levels of 2OG preferred food higher in energy. 

The authors wrote: ‘Taken together, these results suggest that sleep deprivation influences the endocannabinoid system, which in turn alters the connection between piriform and insular cortex, leading to a shift toward foods which are high in calories.’  

After being sleep deprived, volunteers chose foods that were higher in calories, on average six per cent. 

However, they did not eat more calories overall. 

The effects were long-lasting, as participants continued to eat calorie-dense foods the following day, despite having a ‘recovery’ sleep. 

The study is the latest of many to delve into the mechanisms behind why a lack of sleep causes unhealthy food choices.

Previous research has uncovered a cascade of changes in the body that drive sleep-deprived people to high fat, salt and sugar foods.

Most significantly, hunger regulating hormones such as ghrelin and leptin have been reported to increase.

The new research, based on 29 men and women between the ages of 18 and 40, was published in the journal eLife.

Senior author Thorsten Kahnt, assistant professor of neurology at Northwestern University Feinberg School of Medicine, said: ‘People who do not get enough sleep often start to favor sweet and fatty foods, which contributes to weight gain.

‘Our findings suggest that sleep deprivation makes our brain more susceptible to enticing food smells.’

He added that it may ‘be worth taking a detour to avoid your local doughnut shop next time you catch a 6am flight’.

All of the participants were given sleep trackers on their wrist to monitor how much shut-eye they got. 

On the night they were deprived of sleep, the volunteers were only allowed to kip between 1am and 5am. 

To keep participants awake, the researchers advised activities such as watching TV and standing up. 

In the second part of the experiment, the participants had MRI scans taken of their brain before the buffet. 

They were then presented with a number of different smells, including the scent of foods such as gingerbread, cinnamon and caramel.

During the study, doctors observed their piriform cortex, the first area of the brain that receives information from the nose.  

It sends information to the insular cortex, situated deeper inside the brain, which receives signals about smell, taste, and how much food is in the stomach. 

These factors influence how much food we end up eating, the researchers wrote.

Sleep-deprived participants had more activity in the piriform cortex, suggesting they were percieving food smells more than after a normal night’s sleep.

But the insula cortex also showed reduced communication with the piriform cortex, suggesting smells were not being fully understood.  

Professor Thorsten said: ‘When you’re sleep deprived, these brain areas may not be getting enough information, and you’re overcompensating by choosing food with a richer energy signal.

‘When the piriform cortex does not properly communicate with the insula, then people start eating more energy-dense food. 

‘But it may also be that these other areas fail to keep tabs on the sharpened signals in the olfactory cortex. That could also lead to choosing doughnuts and potato chips.’

HOW IS SMELL LINKED TO FOOD CHOICES? 

Smell is an important characteristic of food and is known to influence food choices – what we decide to eat and how much of it.

Even when we are full the sight – which also plays a huge role in what we eat – or smell of a desirable food can stimulate appetite to go in for a second helping.

You only need to think of freshly baked bread or pastries to know how appetising odours can be.  

Exposure to such smells makes our mouths salivate and increases feelings of hunger that may have not been there before.  

On the other hand, people report to be less hungry after cooking a meal, which is long exposure to smell. 

The olfactory system may be linked with a person’s weight, considering studies have suggested exposure to a desirable savory smell increases reactivity to foods, leading to a general desire to eat.

This means that, for some, people are driven to snack more than others, because food odour is a powerful stimulus for their appetite. But people respond differently to the food in their environment.

LACK OF SLEEP MAKES PEOPLE MAY MORE MONEY FOR JUNK FOOD

A lack of sleep makes people crave junk food and spend more money to get their hands on it, a study by German researchers found in December.

Tiredness can boost activity in areas of the brain related to appetite and comfort eating, and hormones that tell us when we are hungry.

The disruption to the body’s normal functions can lead to an increased likelihood of overeating, and over time, obesity, the researchers suggested.

It may explain why some people are more likely than others to reach for the biscuits by the afternoon. 

Dr Julia Rihm, lead author of the study, and her team enrolled 32 healthy men aged between 19 and 32 for the study.

Participants visited their laboratory for a normal dinner of pasta and veal in a creamy mushroom sauce with an apple and strawberry yoghurt, on two separate nights. 

On each visit they were instructed to either return home after the meal to sleep normally or to spend the night at the lab, where they would be kept awake. 

Their desire for snack foods, brain activity, and hormone levels were assessed the next morning. 

Then they were given three Euros (£2.70/$3.40) to spend on snacks – such as popular brands of German chocolate bars or chips – or everyday household items or university merchandise.

In an online auction, images of the goods flashed up on screen with prices going up in stages of 0.25 Euros (£0.22/$0.28).

The participants were told to bid the maximum amount they were willing to spend on the item and that they could spend their total of three euros if they wanted to. 

Only after sleep deprivation were the participants willing pay extra for the junk food items – which they were allowed to eat afterwards.

Using MRI (magnetic resonance imaging) brain scans, the team showed losing sleep fired neurons in their amygdala and hypothalamus.

The amygdala is an area of grey matter that has been linked to reward seeking behaviour – such as eating under stress. The hypothalamus controls appetite.

The results showed an increased amount of activity in these parts of the brain in those who had lost shut-eye. 

The study was published in the Journal of Neuroscience.

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