It’s easy to assume that people with obesity enjoy food more than people in smaller bodies – but it’s not true. Instead, people seem to gradually get less pleasure from eating as they put on weight.
Now, scientists have discovered why that might happen – and, crucially, how restoring that pleasure response could support healthier eating.
“We tend to think of obesity as a condition driven by excessive pleasure from food – like thinking that people just can’t resist junk food,” Prof Stephan Lammel, a neuroscientist at the University of California, Berkeley (in the US) and senior author of the study, told BBC Science Focus.
“But our study, and others before it, suggest the opposite: over time, the pleasure response to food may actually diminish.”
It’s all to do with dopamine: the chemical messenger in the brain linked with reward, motivation and pleasure that is released when we laugh, listen to music or eat delicious food.
Dopamine is regulated by a brain-signalling molecule called neurotensin. But the scientists discovered that overweight mice had much lower neurotensin levels than normal-weight mice, affecting their dopamine responses to food.
“These findings challenge the common misconception that people with obesity eat just for pleasure – when in reality, much of the eating may be driven by habit or emotional cues, not enjoyment or desire,” said Lammel.
To find this out, the scientists raised a group of mice on a very unhealthy, high-calorie diet – containing 60 per cent fat – so they gained excessive weight.
In their usual cages, these mice preferred to eat their high-fat food over normal, lower-calorie food.
But, when they were taken out of their home cages and given access to high-calorie treats – such as butter, peanut butter or chocolate – they didn’t seem particularly bothered about these foods. By contrast, mice raised on normal diets immediately wolfed down the treats.
The scientists then tried using light to stimulate a brain circuit connected to dopamine. In the normal-weight mice, this made them even more eager to eat the treats – but in the overweight mice, it had no effect, suggesting there was something wrong with their dopamine and neurotensin levels.
The good news? The researchers were able to fix this. When they switched some of the mice back to a normal diet for two weeks, their neurotensin levels, dopamine function and interest in high-calorie food returned to normal.
In other mice, the scientists artificially restored their neurotensin levels genetically. These mice lost weight, became more interested in treat foods, and improved their mood and mobility.
“Importantly, our findings suggest that restoring the pleasure of eating through genetic strategies that target neurotensin signalling could help re-balance food motivation and lead to healthier eating patterns,” said Lammel.
This research was carried out on mice on extremely high-fat diets, so its findings might not be directly applicable to humans with obesity.
However, if it does apply to people, Lammel said: “This opens the door to new therapeutic strategies that don’t just suppress appetite but actually improve how the brain experiences food.”
“That could make it easier for people to maintain a healthy weight without relying solely on willpower or restrictive diets, which are often difficult to maintain.”
About our expert
Stephan Lammel is an associate professor of Neurobiology and Weill Neurohub Investigator at the University of California, Berkeley's Department of Neuroscience. His general focus is on studying the neural circuits that mediate motivation and reward. He is also a member of the Helen Wills Neuroscience Institute.
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