23 December 2009

Movement comes with appetite

Researchers at the Swiss State Institute of Technology (Zurich), working under the guidance of Professor Markus Stoffel, have found that an organism that receives food too often falls into a vicious circle of inactivity, obesity and, ultimately, diabetes. This vicious mechanism is triggered by a molecular switch controlled by insulin. The results of the work are published in the December issue of the journal Nature in the article "Regulation of adaptive behavior during fasting by hypothalamic Foxa2".

Hunger increases activityThe key link of the mechanism identified by scientists is the transcription factor Foxa2.

Transcription factors are proteins that ensure the activation of genes and the conversion of the genetic material contained in them into proteins. Foxa2 is expressed in liver cells, where it is involved in the fat burning process, as well as in two important populations of hypothalamic neurons – the area of the brain that controls circadian rhythms, sleep, eating and sexual behavior. Both in the liver and in the hypothalamus, the activity of Foxa2 is controlled by insulin.

When a person or animal consumes food, beta cells of the pancreas release insulin that blocks the activity of Foxa2. During periods of fasting and insulin deficiency, this transcription factor is active. The authors found that Foxa2 is involved in the synthesis of two proteins in the brain: melanin-concentrating hormone (MCH) and orexin. These signaling molecules trigger various behavioral reactions: food intake and spontaneous motor activity. If mammals are hungry, they are more attentive and physically active, that is, they hunt and look for food. This pattern can be observed on pets waiting for feeding.

Explanation of hypodynamiaIn mice with obesity and hyperinsulinemia, the activity of Foxa2 and, accordingly, the expression of melanin-concentrating hormone and orexin are reduced regardless of whether the animals are hungry or full.

This explains the lack of desire to move in obese people and animals.

In order to prove this observation, the authors created genetically modified mice in whose brain cells Foxa2 was constantly active, regardless of the age of the meal. These mice were characterized by an increased level of metabolism and tissue sensitivity to insulin, as well as increased production of melanin-concentrating hormone and orexin. These animals ate more and moved five times more than normal animals, in which insulin deactivates Foxa2 after each meal. Forced activation of Foxa2 in the brains of mice predisposed to obesity also led to an improvement in glucose metabolism, the disappearance of fat deposits and an increase in muscle mass.

Three meals a day: folk wisdom against the recommendations of the best nutritionistsStoffel believes that the results clearly demonstrate that periods of fasting are necessary to maintain health and normal body weight.

He does not agree with the traditional recommendations of nutritionists to eat often, but in small portions, since insulin is produced by the pancreas after each, even a small snack, which automatically suppresses the desire to move and burn calories. Thus, based on the results of the work, the optimal food regime is the usual three meals a day without any, even the lightest and most useful, snacks.

Portal "Eternal youth" http://vechnayamolodost.ru based on the materials of ETH Zurich: Movement comes with appetite.


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