To be, or not to be obese - that's the challenge: a hypothesis on the cortical inhibition of the hypothalamus and its therapeutical consequences.

Today, obesity is the most urgent unsolved medical problem, with the threat of a decreased life expectancy rate for the first time in medical history. Many obese subjects try to lose weight by dieting and exercising, without success on a long term basis. The only therapy with some effect is bariatric surgery with the impact of sustainable adverse effects only suitable in morbid obesity. Why are the therapies to treat obesity not working? Within the last years, we have become more aware of the role of the brain in energy homeostasis. The three main players within the brain controlling our weight are the cortex for cognition, hypothalamus for vital body functions and limbic-reward system for emotions. One hypothesizes that the failure of the cortex to inhibit the hypothalamus is the main cause of obesity. The evolutionary old hypothalamus constantly seeks for a positive energy balance, always in endeavor to avoid any energy shortage in the future. The hypothalamus is executing its tasks in a parallel mode. It can coordinate a set of vital routines independently, yet simultaneously. For e.g., energy balance, salt balance, body temperature and sleep are executed even in a coma. The hypothalamus is primitive but stable. The cortex in humans is, compared to rodents, much bigger and more complex, while the hypothalamus bears more similarities between these two species. The cortex in humans is evolutionary younger and represents higher cognition, an unique human feature. In contrast to the hypothalamus, the cortex focuses on one problem at a time, thus functioning on an attention-based manner. Due to this serial mode, the cortex uses a large part of its capacity for one problem at a time. Therefore, it can solve more complex calculations than the hypothalamus by thinking about one problem after another. It is even strong enough to veto the hypothalamus, if necessary. If the concentration on weight loss is distorted, the hypothalamus is free of inhibition by the cortex, and the subject will gain weight again. It is suggested that this is why diets do not work in the long term. In anorexic patients, the cortex is fully occupied to control the hypothalamus resulting in extreme weight loss. In obese subjects, the cortex is less disciplined and the hypothalamus will take control again to stimulate positive energy balance. From this viewpoint, the limbic-reward system interacts both with the hypothalamus and the cortex to achieve demands by emotional motivation. The last part of this paper describes a therapeutic strategy based on this hypothesis. We propose a dual approach to fight obesity. First, interventions should be implemented that remind the cortex to control the hypothalamus and second, to stimulate physiological feedback to the hypothalamus.