Fat is a neurobiological issue. The brains of overweight people have more receptors for the neurotransmitter serotonin than those of people of normal weight, suggesting that being overweight may be down to more than just eating habits and may have an origin in brain chemistry.
David Erritzoe and his colleagues at the Neurobiology Research Unit at Rigshospitalet, part of Copenhagen University Hospital, Denmark, used positron emission tomography to map the brains of 47 people of normal weight and 29 overweight people. Drugs that block the serotonin receptor 5-HT2A are associated with weight gain, and in animals, stimulating the receptor causes weight loss, suggesting that this receptor plays a role in regulating body weight. The researchers found slightly higher concentrations of the receptor in overweight people.
Whether the difference in receptor number is a cause or an effect of being overweight remains uncertain, but twin studies suggest that genes are important in determining its prevalence.
"I think it’s important for people with weight problems to know that there may be a neurobiological side to it," Erritzoe says. He presented the work at a meeting of the Society of Nuclear Medicine in San Diego, California, last week.