Omnipresent nutrients suppress appetite and promote movement

Graphic abstract. Credit: Current Biology (2022). DOI: 10.1016 / j.cub.2022.02.067

In experiments on mice, researchers at ETH Zurich show that non-essential amino acids have an appetite suppressant effect and promote the urge to move. Their research is published in Current Biology and provides insight into the neural mechanism that governs this behavior.

Proteins can suppress appetite, so a high-protein diet can help people lose weight. This is just one of the reasons why this type of diet has become more and more popular in recent years. By working with mice, researchers at ETH Zurich have now demonstrated a new mechanism by which the building blocks of proteins – the amino acids – slow down appetite. Specifically, it involves what are known as non-essential amino acids.

Of the 21 amino acids that our body needs, there are nine that they are not able to produce on their own. They are called essential amino acids. Because we need to get these through our diet, they have long been the focus of nutrition research. The other 12 amino acids are considered non-essential. The body itself can produce them by altering other molecules.

Shown in mouse

It has been known that both essential and non-essential amino acids can suppress appetite. However, for the non-essential amino acids, the mode of action had not yet been demonstrated in living organisms. Now, a group of researchers led by Denis Burdakov, professor of neuroscience at ETH Zurich, have for the first time shown in a living organism that the non-essential amino acids affect the brain in a way that suppresses appetite and promotes exercise.

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The researchers first fed mice with either a mixture of different non-essential amino acids or a sugar solution with the same amount of calories (control group). Both groups of mice were then allowed to drink a milkshake that they usually love. While the control group drank copious amounts of it, the mice that had been fed non-essential amino acids avoided theirs. Instead, they walked around their enclosure in search of alternative food.

Rooted in evolutionary history

With further experiments, the researchers were able to decode the underlying mechanism in which specialized nerve cells in the brain – orexin neurons – play the major role. Proteins that mice absorb through food are broken down in the gut into their amino acids, which then enter the bloodstream. From there, the blood transports them to the brain. The orexin neurons in the hypothalamus have receptors that specifically recognize the non-essential amino acids. In response, they initiate a neural circuit that produces the described behavioral changes.

This mechanism is probably rooted in evolutionary history. “Today we have adequate access to all nutrients and we have plenty of time to eat. In prehistoric times, when this mechanism evolved, this was probably not the case,” said Paulius Viskaitis, postdoc of Burdakov’s group and lead author of the study. . “Back then, it was beneficial for individuals to spend only a short time on a food source that consisted primarily of non-essential amino acids.” If intake of non-essential amino acids promotes the urge to move, the animal will go in search of other food sources – which potentially contain more essential nutrients and are more important to the individual.

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Viskaitis emphasizes that the results can be transmitted to humans and other animals, as this mechanism affects an area of ​​the brain that is very old in terms of evolutionary history and occurs equally in all mammals and many other vertebrates. Still, for people who want to lose weight, a diet that contains particularly high levels of non-essential amino acids may not be recommended everywhere, Viskaitis says. Nutritional recommendations should be made on an individual basis and they should also take into account health aspects.

Essential components of dietary restrictions revealed More information: Paulius Viskaitis et al., Ingested non-essential amino acids recruit brain orexin cells to suppress eating in mice, Current Biology (2022). DOI: 10.1016 / j.cub.2022.02.067

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