Selfish brain theory

The “Selfish Brain” theory describes the characteristic of the human brain to cover its own, comparably high energy requirements with the utmost of priorities when regulating energy fluxes in the organism. The brain behaves selfishly in this respect. The "Selfish brain" theory amongst other things provides a possible explanation for the origin of obesity, the severe and pathological form of overweight. The Luebeck obesity and diabetes specialist Achim Peters developed the fundamentals of this theory between 1998 and 2004. The interdisciplinary “Selfish Brain: brain glucose and metabolic syndrome” research group headed by Peters and supported by the German Research Foundation (DFG) at the University of Luebeck has in the meantime been able to reinforce the basics of the theory through experimental research.

The brain performs many functions for the human organism. Most are of a cognitive nature or concern the regulation of the motor system. A previously lesser investigated aspect of brain activity was the regulation of energy metabolism. The "Selfish Brain" theory shed new light on this function. It states that the brain behaves selfishly by controlling energy fluxes in such a way that it allocates energy to itself before the needs of the other organs are satisfied. The internal energy consumption of the brain is very high. Although its mass constitutes only 2% of the entire body weight, it consumes 20% of the carbohydrates ingested over a 24-hour period. This corresponds to 100 g of glucose per day, or half the daily requirement for a human being. A 30-year-old office worker with a body weight of 75 kg and a height of 1.85 m consumes approx. 200 g glucose per day.

Before now the scientific community assumed that the energy needs of the brain, the muscles and the organs were all met in parallel. The hypothalamus, an area of the upper brainstem, was thought to play a central role in regulating two feedback loops within narrow limits.

On the basis of these theories a number of international research groups still position the origin of obesity in a disorder in one of the two above described feedback systems. However, there are scenarios in weight regulation that can not be explained in this way. For example, upon inanition of the body (e.g. during fasting) almost all the organs such as the heart, liver, spleen and kidneys dramatically lose weight (approx. 40%) and the blood glucose concentration falls. During this time, however, the brain mass hardly changes (less than 2% on average). A further example illustrates the inherent conflict between these two explanatory approaches: although large amounts of the appetite suppressing hormone leptin are released in obese individuals, they are still afflicted with a ravenous hunger once their blood glucose falls.

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