Why being stressed makes us crave junk food

Chronic stress can fuel overeating and obesity, research shows

People are more likely to crave unhealthy foods during periods of stress. Ravindranath K / The National

Stress can disrupt messages in the brain that tell the body when it is full, a study has found.

Scientists at the Garvan Institute of Medical Research in Australia conducted the research and said it showed a link between stress and overeating.

The study, published in the journal Neuron, highlights the importance of maintaining a healthy diet.

“Stress can override a natural brain response that diminishes the pleasure gained from eating – meaning the brain is continuously rewarded to eat," Prof Herbert Herzog, senior author of the study.

“Chronic stress, coupled with a high-calorie diet, can increase food intake and promote a preference for sweet, highly palatable food, thereby contributing to weight gain and obesity.”

Stress and weight gain

Many people tend to eat more than usual when they are stressed and opt for calorie-rich, sugary and fatty foods.

The researchers wanted to understand the reasons for this.

“There are some previous studies that tested that acute stress is likely to suppress food intake behaviour as it will trigger an acute flight or fight response to handle adverse situations," said first author Dr Kenny Ip told The National.

“In our case, we highlighted that it is chronic stress which is the key driver that increases the intake of the palatable diet."

The researchers used mice to see how different brain areas responded to chronic stress in relation to different diets.

The team discovered that chronic stress silenced a part of the brain known as the lateral habenula, which is usually responsible for dampening reward signals and stopping overeating.

“In stressed mice on a high-fat diet, this part of the brain stayed silent, enabling continuous reward signals that encourage feeding for pleasure, disregarding normal signals of fullness,” Dr Ip said.

Stressed mice on a high-fat diet gained twice as much weight as those on the same diet who were not stressed.

“The anatomical structure as well as the function of habenula is highly conserved across all species, including humans," Dr Ip said.

"Particularly, this brain region in both humans and mice is important for regulating emotional responses and now eating behaviour”.

Key molecule in stress-eating connection

The researchers found that a molecule known as Neuropeptide Y, or NPY, which the brain naturally produces in response to stress, was instrumental in driving this behaviour.

Blocking NPY in stressed mice on a high-fat diet meant they ate less and did not gain as much weight.

The researchers also demonstrated that stress leads creates a greater preference for sweet food.

This was shown in an experiment where stressed mice on a high-fat diet consumed three times more artificially sweetened water than non-stressed mice on the same diet.

“We did not observe this preference for sweetened water in stressed mice that were on a regular diet,” Prof Herzog said.

Stress, food, and energy balance

Prof Herzog emphasised that while food can provide a short-term energy boost to cope with stress, long-term stress can disrupt this balance, leading to unhealthy eating habits and obesity.

“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," he said.

Potential treatments and interventions

Dr Ip said NPY controlled "feeding and stress, but is also involved in the regulation of many other functions in the brain".

He said using therapies to target NPY would require precise approaches focused on specific regions of the brain.

An alternate could be to monitor a person's stress levels using blood tests.

"This could potentially provide a parameter to examine if individuals are at risk of excessive weight gain and whether anti-stress treatments could help," Dr Ip said.

When asked about strategies to prevent the damaging cycle of stress and unhealthy eating, Dr Ip emphasised the need for people to watch what they eat.

“We all define comfort food differently and have various hobbies. Recognising prolonged periods of high stress is vital," he said.

“In these instances, we recommend individuals pay extra attention to their meal size, frequency and dietary choices."

Dr Ip said obesity increased the risk of cardiovascular disease, hormonal imbalance, infertility and cancers.

“If stress-induced eating within two weeks in our experimental model already has such profound effects on energy metabolism, it is very likely that the damage can be beyond weight gain and obesity only," he said.