Secret to why stress makes you reach for the chocolate revealed 

Scientists have revealed the secret to why feeling stressed makes you keep reaching for donuts, candies and even chocolate bars.

Australian researchers said that when someone is full, an area of the brain activates to shut off reward signals from food — signaling for them to stop eating.

But in experiments on stressed mice, they found that this area remained silent — prompting the rodents to keep eating for pleasure. Those in the stressed group gained twice as much weight as mice in the non-stressed group. 

The scientists said their study highlights the importance of sticking to a healthy diet, particularly when suffering from chronic stress.

Dr Herbet Herzog, an eating disorders researcher at the Sydney-based Garvan Institute of Medical Research, said: ‘Our findings reveal stress can override a natural brain response that diminishes the pleasure gained from eating – meaning the brain is continuously rewarded to eat.

‘We showed that chronic stress, combined with a high-calorie diet, can drive more and more food intake as well as a preference for sweet, highly palatable food, thereby promoting weight gain and obesity.

‘This research highlights how crucial a healthy diet is during times of stress.’

In the study, published today in the journal Neuron, scientists split mice into two groups and monitored how much food they consumed.

Each was offered the same high-fat diet for a short period of time and was able to eat as much as they want.

One group of mice was kept in laboratory conditions, while the other was subjected to chronic stress.

Scientists did not say how this was achieved, but in previous cases, it has involved suspending mice from their tails for a protracted period until they stop struggling. This is repeated to trigger chronic stress.

Researchers found that the mice in the stressed group gained twice as much weight as the mice on the same diet who were not stressed.

Tests revealed that an area of the brain known as the lateral habenula, which is located next to the thalamus, would remain silent when the mice were stressed.

In the non-stressed mice, this area switched on once they were full — signalling for them to stop eating.

But for those that were chronically stressed, the area did not become activated by satiety, prompting them to carry on eating.

To firm up the results, scientists also performed a ‘sucralose preference test’.

This was when the mice were offered two options, either drinking water or water that had been artificially sweetened.

They found that the stressed mice consumed three times more sucralose than mice that were on a high-fat diet alone.

The researchers said that at the center of this response was a molecule called NPY, which the brain naturally produces in response to stress.

When researchers blocked NPY in stressed mice on a high-fat diet, the mice consumed less comfort food and gained less weight.

Dr Herzog added: ‘In stressful situations, it’s easy to use a lot of energy and the feeling of reward can calm you down.

‘This is when a boost of energy through food is useful.

‘But, when experienced over long periods of time, stress appears to change the equation, driving eating that is bad for the body long term.’

He added: ‘This research emphasizes just how much stress can compromise a healthy energy metabolism.

‘It’s a reminder to avoid a stressful lifestyle, and crucially — if you are dealing with long-term stress — try to eat a healthy diet and lock away the junk food.’

Scientists did not consider other factors that could also be driving the stressed eating in mice, such as a disrupted sleep schedule.

It was not clear whether the results of these experiments in mice were directly translatable to humans.

The research was funded by the National Health and Medical Research Council of Australia.