Science reveals why you can’t resist a snack – even when you’re full

(Press-News.org) Peer reviewed – experimental study - humans

Research from the University of East Anglia (UEA) may finally explain why we still reach for the biscuit tin, even when we’re full.

A new study reveals that the human brain continues to respond to tempting food cues even after we’ve eaten enough.

In a world of endless adverts and snack cues on every corner, the team say their findings shed light on why so many of us struggle to maintain a healthy weight.

Lead researcher Dr Thomas Sambrook, from UEA’s School of Psychology, said: “Obesity has become a major worldwide health crisis. But rising obesity isn’t simply about willpower - it’s a sign that our food-rich environments and learned responses to mouth-watering cues are overpowering the body’s natural appetite controls.

“We wanted to better understand how our brains react to food cues when we are already feeling full.

“We studied people’s brainwaves after eating and found that even though their stomachs might be satisfied, their brains didn’t seem to care.

“In fact, no amount of fullness could switch off the brain's response to delicious looking food. This suggests that food cues may trigger overeating in the absence of hunger.”

How the research happened

In the study, 76 volunteers were monitored using Electroencephalogram (EEG) brain scans as they played a reward‑based learning game with food such as sweets, chocolate, crisps and popcorn.

Halfway through the task, participants were given a meal of one of the foods until they didn’t want another bite.

According to the researchers, the participants really were full - they reported dramatically reduced desire for the food, and their behaviour showed they no longer valued it.

But their brains told a different story.

Electrical activity in areas associated with reward continued responding just as strongly to images of the now‑unwanted food even after participants were completely full.

Dr Sambrook said: “What we saw is that the brain simply refuses to downgrade how rewarding a food looks, no matter how full you are.

“Even when people know they don’t want the food, even when their behaviour shows they’ve stopped valuing the food – their brains continue to fire “reward!” signals the moment the food appears.

“It’s a recipe for overeating.”

A habit you didn’t know you had

The findings suggest that our responses to food cues may work like habits - automatic, learned reactions forged over years of pairing certain foods with pleasure.

Dr Sambrook said: “These habitual brain responses may operate independently of our conscious decisions. So, while you might think you’re eating because you’re hungry, your brain may simply be following a well‑worn script.”

The study found no link between people’s ability to make goal‑directed decisions and their brain’s resistance to food devaluation. That means even people with excellent self‑control can be undermined by automatic neural responses.

“If you’re struggling with late‑night snacking or can’t say no to treats even when you’re full, the problem may not be your discipline - it may be your brain's built‑in wiring,” said Dr Sambrook.

“It’s really no wonder that resisting a doughnut can feel impossible,” he added.

This research was led by UEA in collaboration with the University of Plymouth.

‘Devaluation insensitivity of event related potentials associated with food cues’ is published in the journal Appetite.

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