A Curious View of Obesity

From a recent issue of JAMA:

Several lines of evidence from the study of patients with brain diseases converge on the prefrontal cortex (PFC), especially in the right hemisphere, as a critical area involved in the cognitive control of food intake. The PFC is the part of the brain that has undergone the biggest expansion during evolution, accounting for approximately one third of the surface of the human brain (Figure). Many complex aspects of behavior that distinguish humans from other species originate here, through the confluence of sensory, limbic, and autonomic information. Current theories on the PFC posit a crucial role for this region in the top-down control of behavior, especially under conflicting situations, when inappropriate responses need to be inhibited.

Diverse findings suggest a crucial role of the PFC in obesity. In the mid-1900s, overeating and weight gain were a common side effect in patients who underwent frontal leukotomy, a psychosurgical procedure that disconnects the frontal lobe from the rest of the brain. Damage to the right frontal lobe can cause a passion for eating and a specific preference for fine food, the so-called gourmand syndrome. In patients with degenerative dementia, the presence of hyperphagia correlates positively with right frontal atrophy and negatively with left frontal atrophy. . . . Hyperactivity of the right PFC can lead to anorexia-like symptoms, for example, in patients with right prefrontal focal epilepsy, in which the eating disorder can cease after initiation of anticonvulsant therapy.

Additional data support a link between the right PFC and spontaneous physical activity. . . . The right PFC is preferentially involved in guiding decision making according to social conduct and comprehension of bodily information at a higher level. . . . A dysfunction of the right PFC may represent a central event in the etiology of human obesity. . . . Increasing the activity of the right PFC might decrease appetite and reestablish inhibitory mechanisms controlling eating, as well as improve long-term adherence to interventions such as diet or exercise therapy, which is a major barrier that limits the success of any attempt to treat obesity.

No data to support this prediction are given. I think exercise and diet therapies usually fail because they are based on too-simple ideas about weight control. What does the gourmand syndrome reveal, I wonder.

Reference: The Right Brain Hypothesis for Obesity. Miguel Alonso-Alonso, MD, MPhil; Alvaro Pascual-Leone, MD, PhD. JAMA. 2007;297:1819-1822.