How many times after lunch, even if you ate a whole plate of pasta, feel that hole in your stomach, precise for a piece of cake, or a little chocolate?
And how many times, with all the good intentions of following a decent diet, try to deceive yourself by eating some fruit?
And how many times then, after fruit, give in and also eat any chocolate, finger, candy you are standing in front of?
Eh, I'm sorry, but the brain is not deceived! Rather, better: the intestine is not deceived!
In fact, you must know there are special cells in our intestines that can tell you the difference between sugars rich in calories, for example sucrose, and what we might classify as sweeteners, which also includes fructose.
Duke University researchers discovered these gut nerve cells, capable of transmitting a signal to the vagus nerve, which then sends the message to the brain. For this study, different types of cocktails with different sugars and sweeteners were administered directly to the intestines of laboratory mice and at the same time the electrical activity of the vagus nerve was measured: all sugars activate the signal except fructose. This explains why an apple doesn't give the same satisfaction as a spoonful of Nutella.
We would like to imagine the neurons doing this as little men in a sorting center dividing sugar and sweetener.; but the underlying biochemical mechanism is a little more complicated. It has in fact been seen that only sugar molecules with high caloric intake, exciting these neurons, release glutamate, while sweeteners release ATP. These two different signals, they carry a different message along the vagus nerve which is then translated differently by the brain. In the first case it says “ok, the glycemic intake is quite satisfactory "while in the second" More sugar!”.
But why does our brain need these signals? Because sweet is good?
No, actually there could be a more interesting evolutionary reason: in animals this should lead to the search for a food richer in calories.
in conclusion, if you had to jump from branch to branch or run very fast to eat, it must be worth it, there is no point in doing it for something Sugar-free!
The gut-brain axis is an increasingly studied topic, which in recent years has opened the doors to many different researches. In this particular case, could lead to the study of new sweeteners able to stimulate these neurons and make us feel with a plate of fruit the same satisfaction as the slice of cake that we cannot say no to after lunch!
Buchanan, K. L., Rupprecht, L. E., Sahasrabudhe, A., Kaelberer, M. M., Klein, M. E., Villalobos, J., … & Anikeeva, P. (2020). A gut sensor for sugar preference. bioRxiv.