Brain damage caused by fatty food might be one reason why people who habitually over-eat find it so hard to lose weight, scientists have said.
New research suggests that saturated fat can destroy neurons in a part of the brain that controls energy balance and appetite.
Researchers found changes to vital genes and proteins in the brains of mice fed a high fat diet.
The effects in the hypothalamus - the brain's energy centre - indicated the kind of damage normally caused by inflammation and blood clot strokes.
Lead scientist Lynda Williams, from the University of Aberdeen Rowett Institute, said: "These changes may underlie the breakdown of energy centres in the brain and may explain why its so difficult for obese people to maintain weight loss from dieting.
"Our results indicate that a high fat diet can damage the areas of the brain that control energy balance and perpetuate the development of obesity.
"High fat and high sugar foods are energy dense foods which are highly palatable and they are very easy to over-eat. Our findings may also explain why some overweight people find it difficult to diet and why weight loss after dieting is so difficult to maintain.
"We now plan to carry out further studies that will look at whether these effects are reversible."
She pointed out that brain scan studies in the US had shown signs of hypothalamus damage in obese individuals, suggesting that the effects seen in mice may also occur in humans.
The hypothalamus is a small area at the base of the brain that contains neurons which govern energy expenditure and appetite.
"This control breaks down in obesity - the system appears not to work - and we don't really know why this happens," said Dr Williams, speaking at the British Science Festival at the University of Aberdeen.
"In our study we found that genes and proteins change in response to a high fat diet and that these changes are normally associated with damage to the brain, indicating that damage had occurred in the hypothalamus in mice that ate a diet high in saturated fat."
The changes happened quickly, she said. It took three days for proteins to be affected and a week for visible signs of disruption to genes to appear.
Dr Williams acknowledged the effects might be exaggerated in mice whose diet was drastically altered so they obtained 60% of their energy from saturated fat.
Could these foods cause brain damage?
The results did not mean people having the occasional unhealthy treat risked damaging their brains, she said.
"The key is to avoid excessive weight gain and to eat sensibly in the first place," she added. "We all deserve a treat now and then."
Another study presented at the meeting showed how the way snacks are presented in cafes can alter people's eating habits.
Pictures of healthy, less healthy, and unhealthy items were arranged in a line beneath the number of calories each contained.
The healthiest foods, such as fruit and cereal bars, were on the left and the unhealthiest, such as chocolate and cake, on the right. A message read: "If you want to consume fewer calories today then choose a snack from the left."
Tested in two coffee shops, the sign led people to reduce the energy value of snacks they bought by about 66 calories on average.
Psychologist Dr Julia Allan, from the University of Aberdeen, said: "We're very excited by this. Research from the US has shown that if you consistently reduce calorie intake by about 100 calories that can lead to weight loss."
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