Science News:

The study, led in Australia by the Monash Obesity and Diabetes Institute (MODI) at Monash University, found a high-fat diet causes brain cells to become insulated from the body preventing vital signals, which tell the body to stop eating and to burn energy, from reaching the brain efficiently.
MODI director and Australian Life Scientist of the Year Professor Michael Cowley said there were two clear outcomes from the findings.

'We discovered that a high-fat diet caused brain cells to become insulated from the body, rendering the cells unable to detect signals of fullness to stop eating," Professor Cowley said.

"Secondly, the insulation also created a further complication in that the body was unable to detect signals to increase energy use and burn off calories/kilojoules."

..."Obese people are not necessarily lacking willpower. Their brains do not know how full or how much fat they have stored, so the brain does not tell the body to stop refuelling. Subsequently, their body's ability to lose weight is significantly reduced."