The ubiquitous nutrients suppress appetite and promote movement

Summary: Ingested non-essential amino acids curb appetite and promote movement in mouse models.

Source: ETH Zurich

In experiments on mice, researchers from ETH Zurich have shown that non-essential amino acids act as appetite suppressants and promote the urge to move.

Their research is published in Current biology and provides information on the neural mechanism that controls this behavior.

Protein 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 increasingly popular in recent years. Working with mice, researchers at ETH Zurich have now demonstrated a new mechanism by which the building blocks of proteins, amino acids, reduce appetite. Specifically, it involves what are known as non-essential amino acids.

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

Indicated in mice

It is known that essential and non-essential amino acids can suppress appetite. However, for non-essential amino acids, the mode of action had not yet been demonstrated in living organisms.

Now, a team of researchers led by Denis Burdakov, a neuroscience professor at ETH Zurich, has shown for the first time in a living organism that non-essential amino acids affect the brain in ways that curb appetite and promote exercise. .

The researchers first gave the mice a mixture of various 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 smoothie, which they normally love.

While the control group drank copious amounts, mice that had been fed non-essential amino acids avoided theirs. Instead, they circled their enclosure in search of alternative livelihoods.

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 main role. The proteins that mice absorb through food are broken down in the intestines into their amino acids, which then enter the bloodstream. From there, the blood carries them to the brain.

Orexin neurons in the hypothalamus have receptors that specifically recognize non-essential amino acids. In response, they initiate a neural circuit that produces the behavioral changes described.

This mechanism is probably rooted in evolutionary history. “Today we have sufficient access to all nutrients and we have plenty of time to eat. In prehistoric times, when this mechanism developed, it probably wasn’t, ”says Paulius Viskaitis, a postdoc in Burdakov’s group and lead author of the study.

This shows a diagram of the study
Protein can suppress appetite, so a high-protein diet can help people lose weight. Credit: Researchers

“Back then, it was beneficial for people to spend only a short amount of time on a food source that consisted mostly of non-essential amino acids.” If eating non-essential amino acids promotes the urge to move, the animal will search for other food sources, which potentially contain more essential nutrients and are more important to the individual.

Viskaitis points out that the findings are transferable to humans and other animals, as this mechanism affects a region of the brain that is very ancient in terms of evolutionary history and occurs equally in all mammals and many other vertebrates.

However, for people who want to lose weight, a diet that mostly includes a lot of non-essential amino acids can’t be recommended across the board, says Viskaitis. Nutrition recommendations should be formulated on an individual basis and should also take into account health aspects.

About this appetite research news

Author: Press office
Source: ETH Zurich
Contact: Press Office – ETH Zurich
Image: The image is in the public domain

Original research: Free access.
“Ingested non-essential amino acids recruit brain orexin cells to suppress eating in mice” by Paulius Viskaitis et al. Current biology


Abstract

See also

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Ingested non-essential amino acids recruit brain orexin cells to suppress eating in mice

Emphasizes

  • Ingested non-essential amino acids (nAAs) activate orexin cells
  • Optostimulation of nAA or orexin cells increases exploration and reduces nutrition
  • CCK-sensitive vagal afferents are not required for nAA effects
  • Cell ablation of orexin abolishes the nAA modulation of feeding and exploration

Summary

Ingested nutrients are proposed to control mammalian behavior by modulating orexin / hypocretin (HON) hypothalamic neuron activity. Previous one in vitro Studies have shown that ubiquitous nutrients in mammalian diets, such as non-essential amino acids (AAs) and glucose, modulate HON in distinct ways. Glucose inhibits HONs, while nonessential (but nonessential) AAs activate HONs. The latter effect is of particular interest because its purpose is unknown.

Here, we show that ingesting a dietary mix of non-essential AAs activates HON and shifts the behavior from eating to exploration.

These effects persisted despite the ablation of a key neural gut → brain communication pathway, the vagal afferents sensitive to cholecystokinin. The behavioral change induced by ingested nonessential AAs was recapitulated by targeted HON optostimulation and abolished in HON-deficient mice.

Furthermore, analysis of the lick microstructure indicated that intragastric nonessential AAs and HON optostimulation each reduce the size, but not the frequency, of consumption attacks, thus implying modulation of food palatability as a mechanism for suppression. of food. Collectively, these findings suggest that a key purpose of ingested, nonessential AA activation of HON is to suppress eating and restart foraging.

We propose and discuss possible evolutionary benefits of this, such as optimizing the stomach’s limited capacity for ingesting essential nutrients.

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