The Nature of Appetite – Juventud Rebelde

Two studies reveal the secret mechanisms behind our cravings for fatty foods

“We live in unprecedented times where excessive consumption of fats and sugars is causing an epidemic of obesity and metabolic disorders. This is how Mengtong Li, author of the study Gut-brain circuits for fat preference, recently published by the journal Nature, describes it.

You and I may think that this is not a discovery. Who does not know, already at the height of this century, that a diet of sugars and fats, constantly promoted by the maelstrom of fast food chains that abound in the world, destroys health indicators? It’s not new, it’s true. But what is currently a mystery being solved is knowing the exact and specific mechanisms by which the body ends up making people almost addicted to this type of junk food.

This research was able to reveal the internal connection between the brain and the gut, which is why, as shown by studies with mice developed by specialists from the Zuckerman Institute of Columbia University, USA, in these animals fat that reaches the gut triggers a signal that is transmitted to the brain through the nerves and causes the subsequent desire to eat fatty food again. What we can colloquially call a whim.

These observations open the door to the possibility of interfering with the connection between the gut and the brain, interrupting the desire for more fat, supporting healthier choices and tackling the growing global problem caused by overeating in some parts of the planet, the authors explained before Nature.

capricious bowels

“If we want to control our insatiable desire for fat, science shows us that the key wire that drives those desires is the connection between the gut and the brain,” said Mengtong Li.

But this “gut weirdness” mechanism isn’t limited to fat. The researchers concluded that sugar activates the same gut mechanism to the brain.

Glucose activates a specific gut-brain circuit that communicates with the brain in the presence of gut sugar. No-calorie artificial sweeteners, on the other hand, do not have this effect.

“Research shows that the tongue tells the brain what we like, that is, what tastes sweet, salty, or fatty,” said Dr. Zucker, professor of molecular biochemistry and biophysics and neuroscience at Columbia’s Vagelos College of Physicians and Surgeons, but , he explains, “however, the gut tells our brain what we want, what we need.”

Mice in the spotlight

During observation, animals were offered bottles of water containing dissolved fat and bottles of water containing sweet substances. In just two days, the rodents showed a preference for water bottles containing fat. They retained their choice even when scientists genetically modified them so that they did not taste fat. Interestingly, although the animals could not taste the fat, they were forced to consume it.

The researchers believe that fat must activate specific brain circuits that govern the animals’ preference for fat. To find these communication pathways, they measured brain activity in mice while they ate fat.

The results showed that neurons in the caudal nucleus of the solitary tract, which are located in the brainstem, the most primitive region of the brain, were activated. Something that also happened in the previous sugar study. Neurons in the vagus nerve, which connects the gut to the brain, also moved when the mice had fat in their guts.

Next, the researchers focused on the gut, specifically the endothelial cells that line it. Two groups of cells were found to send signals to neurons in the vagus nerve in response to fat.

This was explained by the lead author of the study: “A group of cells functions as a common sensor for essential nutrients, responding not only to fat but also to sugars and amino acids,” explains Li. “The other group responded only to fat, potentially helping the brain distinguish fat from other substances in the gut.”

Following the findings, the scientists blocked the activity of these cells by administering a drug to the mice. None of the cell groups signaled anything, and the vagus neurons did not respond to the fat in the gut. They also used genetic techniques to turn off these vagal neurons, and in both cases the mouse lost interest in fat.

What about sugar?

In addition to this team’s studies, another discovery about the effect of sugar on gut microbiota has arrived in parallel with these studies of “cravings” and their mechanisms.

Gut microbiota can work to benefit our health, but sugar transforms it.

Another study in mice found that dietary sugar alters gut microbiota in ways that lead to metabolic disease, prediabetes and weight gain.

A Western diet high in fat and sugar can cause obesity, metabolic syndrome and diabetes, but until now the exact mechanism by which it causes these changes in the body was unknown. In recent years, it has been discovered that gut bacteria can have a much greater influence than previously thought.

The gut microbiota, which is essential for the nutrition of all animals, has been extensively studied in a mouse population. Researchers at Columbia University decided to take a closer look at the effects of a Western-style diet on the microbiota of laboratory mice.

After four weeks on the diet, the animals showed symptoms of metabolic syndrome, including weight gain, insulin resistance and glucose intolerance. Their microbiomes have changed dramatically, with a complete change in gut bacteria.

Now, with the results of the two studies, it will be possible to think of pharmacotherapeutic ways to interrupt this intestinal-neuronal connection to avoid fat hunger, as well as methods to prevent the negative transformation of the microbiota of good intestinal bacteria in the presence of sugar .. Let’s hope that our habits accompany so much effort.

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