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Signals from our belly to the brain
Our body requires energy to function. Every cell needs a certain amount of nutrients to keep working properly and face every day’s stress, so it is normal for our body to ask for those nutrients in the form of appetite and hunger. If you have noticed, we feel hungry several times a day, depending on our energy requirements. So, we are not eating all the time, without a reason; instead of this, our body knows when to request food and when not to. How is food and energy intake controlled, then? As you can imagine, our brain does all the work through chemical and electrical signals that go from our gut to the brain and viceversa.
There are two main signals that our brain relies on to control energy intake, and they are satiation and satiety. The first one tells our body that enough nutrients have been consumed in order to satisfy energetic requirements. Satiation is basically when we feel full and stop eating. Satiety, on the other hand, has to do with how long this feeling of fullness lasts, until we feel hungry again.
Both amount and number of meals affect the total energy intake in one day.
The food intake and energy regulation mechanisms start even before you put anything in your mouth. Here, our senses, including the smell, the sight and even the touch, play an important role. Behavioral changes start occurring when we see food that looks attractive to us, based on its appearance or in previous experiences.
The brain in action
After eating, our stomach distends, or increases in size.
After this, food reaches the small intestine, where nutrients are absorbed. Here, liberation of substances also activates regions of the brain that continue with the satiation and satiety signals. Cholecystokinin (CCK) is a hormone that is secreted as a response to the detection of fats and proteins from food.
Satiety is controlled by other gut hormones that not only act at the same time as CCK, but their effects also tell the brain how much energy is left from the last meal.
Other gut hormones that participate in the promotion of satiety are the glucagon-like peptide, oxyntomodulin, peptide YY and pancreatic polypeptide. All these slow down gastric emptying in order to maintain a constant satiety signal, until it is necessary for us to eat again to fulfil energy requirements. This is why we aren't eating all the time. Our brain knows when to stop and when to eat again thanks to these hormones.