Eating too much fatty food can damage nerves in the stomach that tell the brain we are full, scientists believe.
An unhealthy diet can alter the balance of bacteria in the gut - encouraging those that thrive on fat to multiply and killing off others which prefer healthier food. This can lead to inflammation of the nerves so the brain no longer senses signals telling us we have eaten enough, US scientists think.
They said their research on rats found higher-fat diets altered the animals' brains.
Krzystof Czaja at the University of Georgia said: "When we switch the rats to a high-fat diet, it reorganises brain circuits. It induces inflammation in the brain regions responsible for feeding behaviour. Those reorganised circuits and inflammation may alter satiety signalling." He said this change can lead to "gut-brain miscommunication" - such as thinking we are still hungry even though we have eaten plenty. It is not known whether the change is permanent.
In days gone by, our bodies would have been used to foods derived from natural sources. So the researchers speculate that artificial and highly processed foods might upset the balance of bacteria in our guts and end up confusing our brains.
Dr Czaja said: "In the regular physiological state, many different strains of bacteria live in a balanced environment in the intestinal tract. They don't overpopulate.
