Lack of sleep makes people crave junk food and fork out more money to get it than normal, study finds
- MRI scans showed a boost of activity in areas of the brain linked to appetite
- Participants were more likely to buy chocolate and biscuits after losing sleep
- It’s another link between obesity and sleep deprivation, the experts said
A lack of sleep makes people crave junk food and spend more money to get their hands on it, a study has found.
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.
Britain and US are among the most overweight and sleep deprived nations in the world – and evidence is growing the two are linked.
A lack of sleep makes people crave junk food and spend more money to get their hands on it, a study at Cologne University in Germany found
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.
COULD OBESITY BE A HORMONAL PROBLEM?
A hormonal problem could be making people obese, research published in August found.
Scientists from the University of California San Diego managed to explain a condition called leptin resistance for the first time.
The condition was already known about but not well understood.
In an experiment on mice, the experts found those fed a high fat diet produced an enzyme which damaged hormone receptors in the brain.
As a result, the hormone leptin – which tells the body when a person is full after eating – could not be absorbed, so the signal could not get through.
This means people with leptin resistance may continue to eat more than they need to because their body does not know it’s full.
The scientists said blocking the damaging enzyme – which they could do with medicine – would make the fullness response work properly so people would eat less.
The findings were published in the journal Science Translational Medicine.
Dr Rihm said: ‘We found a full night of sleep deprivation compared with a night of habitual sleep increased the subjective values of snack food rewards compared with non-food rewards.’
She added: ‘These data suggest one way a lack of sleep can promote overeating and obesity risk.
‘This behavioural result was paralleled by increased amygdala and hypothalamus activity selectively after sleep deprivation.
‘Furthermore, the connectivity between the amygdala and hypothalamus was increased after sleep deprivation for food rewards.’
Blood tests also showed levels of ghrelin, the hormone that tells us to eat, were higher.
Dr Rihm said: ‘We found ghrelin concentrations were increased after sleep deprivation compared with habitual sleep.
‘Despite similar hunger ratings due to fasting in both conditions, participants were willing to spend more money on food items only after sleep deprivation.’
Dr Rihm added: ‘Sleep loss is associated with increased obesity risk, as demonstrated by correlations between sleep duration and change in body mass index or body fat percentage.’
Staying up all-night without eating – which is what happened in the study published in the Journal of Neuroscience – is unlikely to happen in real life.
However, Dr Rihm said the findings are still representative of how sleep deprivation builds up over a period of time.
Their results suggest that a lack of sleep may encourage more eating by disrupting the subjective value of food.
Dr Rihm and colleagues added this ‘thereby potentially increases the likelihood of overeating and consequentially weight gain and obesity risk.’
WHAT IS OBESITY? AND WHAT ARE ITS HEALTH RISKS?
Obesity is defined as an adult having a BMI of 30 or over.
A healthy person’s BMI – calculated by dividing weight in kg by height in metres, and the answer by the height again – is between 18.5 and 24.9.
Among children, obesity is defined as being in the 95th percentile.
Percentiles compare youngsters to others their same age.
For example, if a three-month-old is in the 40th percentile for weight, that means that 40 per cent of three-month-olds weigh the same or less than that baby.
Around 58 per cent of women and 68 per cent of men in the UK are overweight or obese.
The condition costs the NHS around £6.1billion, out of its approximate £124.7 billion budget, every year.
This is due to obesity increasing a person’s risk of a number of life-threatening conditions.
Such conditions include type 2 diabetes, which can cause kidney disease, blindness and even limb amputations.
Research suggests that at least one in six hospital beds in the UK are taken up by a diabetes patient.
Obesity also raises the risk of heart disease, which kills 315,000 people every year in the UK – making it the number one cause of death.
Carrying dangerous amounts of weight has also been linked to 12 different cancers.
This includes breast, which affects one in eight women at some point in their lives.
Among children, research suggests that 70 per cent of obese youngsters have high blood pressure or raised cholesterol, which puts them at risk of heart disease.
Obese children are also significantly more likely to become obese adults.
And if children are overweight, their obesity in adulthood is often more severe.
As many as one in five children start school in the UK being overweight or obese, which rises to one in three by the time they turn 10.