A hormone that is known to be involved in regulating appetite also controls people’s fondness for food, scientists have discovered.

Research at the University of Cambridge has found that leptin, which is key to reducing hunger and causing feelings of fullness after eating, also affects emotional responses to food.

While hunger is a critical influence over what and how much we eat, it is not the only influence on food consumption. Eating, of course, is also a pleasant experience that activates reward centres in the brain, and this can override natural curbs on appetite and cause overeating.

A full understanding of eating behaviour and its link to obesity thus requires knowledge of how the brain responds to the sight, smell, taste and even the thought of food.

The Cambridge team, led by Sadaf Farooqi and Paul Fletcher, sought a connection between the brain circuits that tell people when they are full and those that regulate desire for food, and postulated that leptin might be involved in both processes. The hormone is produced by fat cells, and levels normally rise in response to eating, stimulating satiety in the brain and telling it to lose its appetite.

In the study, published in the journal Science, the researchers investigated patients who ate to excess because of a rare genetic disorder that meant they lacked leptin completely.

The subjects were asked to look at pictures of food and nonfood items, while their brains were scanned. In the patients who lacked leptin, areas of the brain known as striatal regions responded to pictures of food. These areas are involved in processing rewards. One of these regions, known as the nucleus accumbens, was particularly responsive to appetising foods.

Among healthy people, the nucleus accumbens was active only when they were hungry. In those who lacked leptin, however, it was also active immediately after they had eaten. Treatment with leptin produced a more normal pattern of activity.

Explore Health

• Expert Advice

• Health Features

• Mental Health

• Alternative Medicine

• Child Health

• Health Club