It’s science, baby! Why you can’t resist snacks, even when you’re full

It is an all-too common feeling – you promise yourself this will be your last chocolate bar, biscuit, or crisp, only to succumb to another.

It could be failing willpower, but a study has suggested that the impulse to keep snacking is the result of our minds working against us.

Researchers at the University of East Anglia (UEA) measured electrical activity in the brains of people shown images of high-calorie foods such as meringues, sweets or crisps.

They discovered that even after participants ate as much of a food as they desired, the strength of their response to pictures of it did not change.

The findings shed light on why so many of us struggle to maintain a healthy weight while bombarded by adverts for calorific snacks on billboards, television and social media.

“Rising obesity isn’t simply about willpower – it’s a sign that our food-rich environments and learned responses to mouthwatering cues are overpowering the body’s natural appetite controls,” said Dr Thomas Sambrook, the lead researcher from UEA’s School of Psychology.

He added that our primitive brains may be to blame, as “we never evolved appropriate responses” to cope with the sheer volume of calories available from processed foods.

The study, published in the journal Appetite, asked 95 hungry people to rank 11 foods on a scale of one to 10 for how much they liked them. Options included breadsticks, sherbet sweets and jelly.

After having electrodes attached to their heads, the participants were made to play a game, designed to activate the reward system in their brains.

They were given two buttons, one of which was more likely to cause an image of one of their favourite foods to pop up on a screen. The other more often produced a picture of an empty cupboard.

Halfway through the experiment, participants ate as much of one of their preferred foods as they wanted, before performing the task again.

“No amount of fullness could switch off the brain’s response to delicious-looking food.”

Dr Thomas Sambrook, University of East Anglia lead researcher

Despite stating they were no longer interested in eating the food and showing less interest in obtaining it, demonstrated by them pressing the wrong button more often, the results of the brain scans were “no different”, Dr Sambrook said.

Each time an image of food popped up, the participants’ brains experienced a wave of electrical activity for the first 1,000 milliseconds.

“This suggests that even though their stomachs might be satisfied, their brains didn’t seem to care,” Dr Sambrook said. “In fact, no amount of fullness could switch off the brain’s response to delicious-looking food.”

Humans produce two hormones that regulate hunger: ghrelin makes us crave food when blood sugar is low while leptin makes us stop feeling hungry when we are full.

However, the unanimous results showed that competing biological imperatives could force our brains to desire food, even as hormones in our bodies tell us we are full.

“The mind is an unruly mob of different processes trying to gain hold of our behaviour,” said Dr Sambrook, explaining that these competing instincts are likely to be a hangover from our prehistoric ancestors.

He said: “We are born with a system that’s calibrated to an ancestral environment of reasonably low-energy foods. The evolutionary boundaries our bodies are experiencing do not contain within them the possibilities of how many calories you get in a tub of golden syrup.”

This response has been heightened by the “ubiquity” of mental cues in adverts as well as our brains’ ability to associate potentially arbitrary cues, such as a chocolate wrapper, with this hardwired sensation, he added.

As a result, “survival of the fittest” has been turned on its head, with snack manufacturers competing to persuade us to gorge on their products rather than humans competing for limited food supplies.

Rather than relying on willpower to stop snacking, Dr Sambrook said, successful avoidance was “much more about arranging your environment so that you are not exposed to cues”.

The Telegraph (London)