Obese people feel a stronger temptation to eat because their brain is wired differently from their slimmer counterparts, a new study claims.
Cooking smells or appetising food adverts have a stronger pull for obese people than their leaner counterparts because of differing levels of ‘pleasure chemical’ dopamine.
Dopamine is a chemical messenger in the brain and influences reward, motivation and habit formation.
It is known as the ‘pleasure chemical’ because it is released when something good happens unexpectedly, such as food being available.
Most drugs cause the release of dopamine, so it is thought to contribute to why some can be addictive.
U.S. researchers found that obese people tended to have greater dopamine activity in the region of the brain that controls habit, and less activity in the region of the brain that controls reward.
These differences in brain chemistry meant obese people ate out of habit and found eating less rewarding than leaner people.
They were more susceptible to environmental food cues, like the smell of food, which made them overeat. But they also did not get the same level of satisfaction from eating as slimmer people.
The study looked at 43 men and women with varying amounts of body fat.
Lead author Dr Kevin Hall, a senior investigator at National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) in the U.S. said the eating out of habit rather than making conscious choices could be detrimental for maintaining a healthy weight.
He said: ‘While we cannot say whether obesity is a cause or an effect of these patterns of dopamine activity, eating based on unconscious habits rather than conscious choices could make it harder to achieve and maintain a healthy weight, especially when appetizing food cues are practically everywhere.
‘This means that triggers such as the smell of popcorn at a movie theatre or a commercial for a favourite food may have a stronger pull for an obese person – and a stronger reaction from their brain chemistry – than for a lean person exposed to the same trigger.’
In tests the participants followed the same eating, sleeping and activity schedule.
A detailed questionnaire was used to record the tendency to overeat in response to triggers in the environment, while scans evaluated the areas of the brain where dopamine was able to act.
Director Dr Griffin Rodgers said: ‘These findings point to the complexity of obesity and contribute to our understanding of how people with varying amounts of body fat process information about food.
He added: ‘Accounting for differences in brain activity and related behaviours has the potential to inform the design of effective weight-loss programmes.’
However, he noted that the study did not demonstrate cause and effect among habit formation, reward, dopamine activity, eating behaviour and obesity.
Future research will examine dopamine activity and eating behaviour in people over time as they change their diets, physical activity, and their weight.
The results were published in the journal Molecular Psychiatry.