Researchers found that rats that binged on fatty food had a hypothalamus desensitised to blood lipid levels, leading to a loss of control over appetite.
Normally, the hypothalamus senses blood lipids when they are converted to specific long-chain fatty acids. It uses the level of these fatty acids to determine appetite and blood sugar levels.
Over-feeding causes cells in the hypothalamus to metabolise blood lipids quickly, before they can be turned into the long-chain fatty acids. This is why rats given a lard-based diet overeat, developing severe hepatic insulin resistance in just three days.
The researchers re-sensitised the hypothalamus to blood lipid levels using a drug to inhibit the enzyme that metabolises them.