Australian scientists have found that chronic stress, in combination with comfort eating, leads to uncontrollable over-eating.

It does this by switching off or sidelining the part of the brain that usually triggers an unpleasant discomfort when you’ve eaten too much.

In experiments, stressed mice on a high-fat diet gained twice as much weight as mice on the same diet that were not stressed.

That’s because they kept on eating for the pleasure of it and way past the point that the non-stressed mice felt full.

What’s happening in the brain?

The new paper from the Garvan Institute of Medical Research, in Sydney, has built on previous research by identifying the triggers to changes in the brain.

The main finding is that “stress combined with calorie-dense ‘comfort’ food creates changes in the brain that drive more eating, boost cravings for sweet, highly palatable food and lead to excess weight gain”.

But the new study, using mouse models, goes further.

The lateral habenula usually dampens signals that promote eating highly palatable food.

It finds that stress over-rides the brain’s natural response to satiety or fullness by triggering “non-stop reward signals that promote eating more highly palatable food”.

The stress and comfort food combo switches off the part of the brain, the lateral habenula, that guards against over-eating.

It does this by dampening those reward signals and lets you know that you’re full. In other words, ordinarily this part of the brain diminishes the pleasure you get from eating once you’ve stuffed yourself.

The mouse investigation

The investigators tested how different areas in the mouse brain responded to chronic stress when consuming “various diets”.

First author Dr Kenny Chi Kin Ip, from the Garvan Institute, said:

“We discovered that an area known as the lateral habenula, which is normally involved in switching off the brain’s reward response, was active in mice on a short-term, high-fat diet to protect the animal from overeating.

“However, when mice were chronically stressed, this part of the brain remained silent. This allowed reward signals to stay active and encourage feeding for pleasure, no longer responding to satiety regulatory signals.”

The bottom line

Senior author Professor Herbert Herzog advises: “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.”

The findings, he said, serve as “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”.

It might help to get more exercise, take up dancing or adopt stress-relieving interventions such as meditation.

Stress and eating

The new study is supported by previous research.

When you’re acutely stressed, from grief or when facing a physical threat, your body works to keep you upright. Part of that process is a drop in appetite. There is no inclination to eat, which in itself is a mildly stressful event.

How does this happen? A short-term spike in adrenalin helps trigger the body’s primal fight-or-flight response. This shuts down eating and ponderous thinking for a while.

When you stay stressed …

When you’re chronically stressed, the body responds by releasing the hormone cortisol. This lifts your motivation to eat. You may have experienced this in a difficult work environment, or in a relationship that grinds more than hums.

Why does this occur? To ensure that you have the energy for coping with the exhausting demands of your stressful situation.

For early humans, under constant stress, it was a matter of eating anything that could be chewed and swallowed.

Let them eat cake

In modern times, we’re more likely to reach for “comfort” foods. Think of those sweet and tasty treats, such as chocolate, that deliver a sense of wellbeing.

Scientists have been poking at this relationship, between stress and comfort eating, for years. Most of this research has involved animal studies.

A 2013 study found that adult rats reared in a stressful neonatal environment – given a rough time as babies – “demonstrate more anxiety and stress, and they prefer to eat more foods rich in fat and sugar”.

A 2017 study found that stressed mouse mothers were more likely to give birth to pups that would go on to exhibit behaviour similar to binge-eating later in life.

This academic interest spiked during COVID-19 lockdowns, when it was perceived that entire households were spending hours face-down in tubs of ice cream as a means of dealing with the great viral unknowns.

A vicious if somewhat tasty cycle

A 2013 paper, Stress and Eating Behaviours, reported that stress is an important factor in the development of addiction and in addiction relapse.

This includes addiction to food. Hence, stress brings an increased risk for obesity and other metabolic diseases.

The authors noted that uncontrollable stress “changes eating patterns” and promotes the “consumption of hyper-palatable foods”.

Over time, they wrote, this “could trigger neurobiological adaptations that promote increasingly compulsively behaviour”.

In other words, stress-related cake-eating leads to changes in the brain that further promotes … stress-related cake-eating.