What makes some people eat even when they are not hungry? They follow a road that leads to obesity. Dardo Tomasi of National Institutes of Health in USA explained to Savvy Soumya Misra why the brain refuses to take the hint

On what happens after food is eaten

Once the stomach is distended with food there is pressure on it walls which activate the mechanoreceptors lodged in them. The receptors send signals to the brain which say stop eating. In obese people the effects of gastric distension are negated.

On why the research was conducted

Obesity is a complex health problem, one for which a single cause cannot be pinpointed. We wanted to find out exactly what it was that made one obese, why people continue eating on a full stomach.

On how it was conducted

We placed balloons in the volunteers’ stomachs, filled with 700 ml water at room temperature. We had earlier used this method to monitor people with normal body weight. A technique called fMRI or functional magnetic resonance imaging allowed us to study the brain functions, particularly its BOLD (blood-oxygenation-level-dependent) response to the signals we sent to the brain. We did that by changing the balloon’s volume.

On the results

Brain regions that are stimulated by the signals increased their activity which, in turn, induced the brain to release dopamine and serotonin. Both chemicals regulate food intake: in times of starvation they promote eating and when the stomach has had its fill they say stop eating. We found that in obese people, a higher body mass index prevented their brain regions from generating adequate ‘stop eating’ signals after the person had had his fill.

On how to take the study forward

We are investigating the visual appeal of food on people and also how different types of tastes affect the brain. This will help us understand how the brain reacts to different foods. We would also replicate our experiments with a larger group of obese people.