Scientists are linking obesity with inflammation and scarring in the key brain area that controls weight, which could explain why it’s so hard to lose weight and keep it off.

When researchers switched mice and rats genetically bred to become obese from low-fat chow to high-fat and highly palatable chow, they began showing signs of inflammation in the hypothalamus within 24 hours.

The hypothalamus takes signals from body fat and other tissues that tell the brain we need food or we’ve had enough. It also regulates how much fat we burn.

“We saw direct evidence of neuron injury and, ultimately, after months on the diet, a loss of neurons in this hypothalamic area that’s vital for body weight control,” said lead researcher Dr. Michael Schwartz, professor of medicine and director of the Diabetes and Obesity Center of Excellence at the University of Washington, Seattle.

The switch to the high-fat diet “is actually injuring the neurons that are supposed to protect them from obesity,” he said.

Brain scarring may help explain obesity battle, study finds