Fat jabs have helped millions slim down, in part due to their action on the gut, but also by silencing the 'food noise' that drives people to overeat.

Now researchers have uncovered how this silencing effect works in the brain – which may open the door to the drugs being used for other conditions, including pain.

Weight-loss jabs – or GLP-1 agonists – are taken by an estimated 2.5 million people in the UK and work by mimicking the action of a hormone, glucagon-like peptide-1, which we produce after eating.

The once-weekly injections slow down the rate at which the stomach empties and make you feel full quickly and for longer.

But scientists have now discovered the GLP-1 agonist tirzepatide (brand name Mounjaro) may have a previously unknown effect on brain waves – and this is what helps silence 'food noise'. (Many fat-jab users say they find they stop thinking about food so much.)

Food noise is a common problem, affecting around 60 per cent of people with obesity, according to a US survey of people taking semaglutide for weight management presented at the European Association for the Study of Diabetes conference last year.

As well as binges, food noise is a factor with anorexia – where people restrict their food intake and have a fear of gaining weight – as it causes those affected to feel preoccupied by food or dieting. 

However, researchers have now discovered that Mounjaro appears to slow brain waves, known as delta-theta oscillations, that trigger food noise.

Previous research, published in Nature Medicine in 2022, found there is a distinctive rise in low-frequency electrical activity in the nucleus accumbens – an area of the brain that helps regulate motivation, pleasure and impulse control – just before someone experiences the urge to binge, but not when they are simply hungry.

Researchers had been looking at whether electrical stimulation (via electrodes implanted in the brain) could help reduce the overactive brain waves and so cut the urge to binge-eat in people with treatment-resistant obesity.

This kind of stimulation is already used to treat drug-resistant epilepsy and Parkinson's with some success.

But now researchers at the University of Pennsylvania have found that taking Mounjaro seems to offer a simpler approach, and stops these brain waves from intensifying – for months on end.

Three patients with severe food noise (who had not found relief through gastric-bypass surgery, behavioural therapy or standard medications) had brain implants surgically put into the nucleus accumbens.

They were asked to swipe a device over the area when they felt the urge to eat, which prompted the implant to record the brain signals.

The participants also swiped when they had no desire to eat. Only one of the three was taking Mounjaro – a 60-year-old woman.  

For the other two, the electrodes recorded significant increases in delta-theta waves every time they experienced food noise.

However, the woman taking Mounjaro reported almost no episodes of food noise and the brain waves did not power up.

After about five months, the volunteer had stronger delta-theta waves and increased food noise, suggesting that Mounjaro only has a temporary impact.

The study, published in Nature Medicine in November, is one of the first in-human trials to investigate Mounjaro's effect on the brain – and could help guide binge-eating research.

It may have other applications too, as the same brain waves that stimulate food noise are also implicated in chronic pain and more.

Developing ways to treat food noise 'is of utmost importance', said Casey Halpern, a professor of neurosurgery at the University of Pennsylvania, who led the new study.

While emphasising the need for further research, he believes the finding may lead to other uses for Mounjaro – which could mean no need for any surgical intervention if it can be modified to last longer.

Dr Simon Cork, a senior lecturer in physiology at Anglia Ruskin University, said the results are 'very interesting', but should be viewed with caution as 'this is only one patient with a specific condition that is associated with obesity and so shouldn't be generalised to the entire population'.

Tom Quinn, director of external affairs at Beat, an eating disorder charity, adds that 'this study has shown positive results for a participant with binge-eating disorder, but more research is needed.

'At the moment we're particularly concerned about what happens when someone stops taking these drugs, as their eating disorder symptoms may reappear or worsen.'

Other ways of calming overactive brain waves linked to conditions such as chronic pain are being investigated.

For example, researchers at the University of South Wales in Australia have developed PainWaive, an interactive game with a headset. 

The headset 'reads' the brain waves and alters the game to calm brain waves associated with chronic pain. Early results, published in the Journal of Pain last year, were promising.

Manipulating brain waves is also being investigated for Alzheimer's. Scientists at Massachusetts Institute of Technology in the US have been exploring whether altering gamma brain waves had memory benefits.

Their device comprises special glasses and headphones which emit lights and sounds designed to stimulate longer-wave gamma oscillations – exposure to which can improve memory – compared to controls. Larger trials are under way.