Is overeating by obese people like drug addiction?

The desire to overeat in obese people is controlled by the same part of the brain that controls cravings for drugs in addicts, according to research. Scientists have found that compulsive eating is regulated by the emotional centres in the brain, leading some people to overeat in an attempt to feel better. Their results were published yesterday in the Proceedings of the National Academy of Sciences.

"This study opens new territory in understanding how the body and brain connect to each other, and how this connection is tied to obesity," said Gene-Jack Wang of the Center for Translational Neuroimaging at the Brookhaven National Laboratory, New York. "We were able to simulate the process that takes place when the stomach is full, and for the first time we could see the pathway from the stomach to the brain that turns 'off' the brain's desire to continue eating."

How a person's brain encourages overeating has, until now, been poorly understood because of the complex way that the body regulates food intake. Hormones such as ghrelin are released when the body wants nutrients and they encourage us to eat. When we have had enough a combination of different hormones and electrical signals from the stomach to the brain tell us to stop eating. The latter is controlled by the vagus nerve, which controls the movement of food through the digestive system.

Dr Wang's team studied seven obese volunteers implanted with gastric stimulators for up to two years. This pacemaker-like device stimulates the vagus nerve, causing the stomach to expand and send a message to the brain to stop eating. Gastric stimulators have successfully been used in obese patients to reduce appetite.

Each volunteer was placed in a positron emission tomography (PET) scanner and brain activity measured when the gastric stimulator was on and then off. "We found that implantable gastric stimulators induced significant changes in metabolism in brain regions associated with controlling emotions, effectively shutting down these obese subjects' desire to eat," said Dr Wang.

The changes were most noticeable in the hippocampus area of the brain. This is linked to emotional behaviour, learning and memory, movement, and processing of sensory information. In people addicted to drugs the hippocampus also plays a role in maintaining the memory of drug experiences.

Stimulating the vagus nerve also sent messages of fullness to other parts of the brain: the orbitofrontal cortex and the striatum. Both of these are associated with craving and desire for drugs in addicts.

Each volunteer was also asked to answer questions that measured three different aspects of eating behaviour - personal restraint, uncontrolled eating and emotional eating. The researchers used the information to correlate which type of eating behaviour was linked to which part of the brain. They found that when the gastric stimulators were switched on volunteers were 21% less interested in the idea of emotional eating - consuming large amounts of food without being hungry - than when they were off.

"This provides further evidence of the connection between the hippocampus, the emotions and the desire to eat, and gives us new insight into the mechanisms by which obese people use food to soothe their emotions," said Dr Wang. "This new pathway should be explored in further studies to determine if there are any implications for treating or preventing obesity." 

-Guardian