To avoid gaining weight, there is a secret that many people know: be sure to chew and swallow slowly when eating.
There are numerous studies proving that healthy people are more likely to become overweight if they eat quickly. For example, a researcher conducted an 8-year follow-up survey on more than 500 men and found that those who ate the fastest gained an average of 3.8 pounds in weight, while those who ate at a medium or slower pace only gained 1.4 pounds. catty.
Chewing slowly can avoid overeating. A well-known explanation is that the stomach sends a "full" signal to the brain. Chewing slowly can allow the brain to respond to the satiety signal in time; and if you eat Too fast, and the brain has no time to respond, causing it to continue eating. By the time you realize you are full, you are actually full and have taken in far more calories than you need.
However, scientists at the University of California, San Francisco (USCF) recently used cutting-edge neural recording technology to directly test this claim in awake mice for the first time, and unexpectedly discovered that this is not entirely true: in fact, The signal that tells the brain to stop eating not only comes from the stomach. During the process of chewing slowly, the brain can tell us to stop eating based on signals from the mouth and tip of the tongue. Their findings have just been published in the top academic journal Nature.
The researchers explained in the paper that from a nervous system perspective, the behavior of stopping eating is controlled by specialized neural circuits, and the brain combines various sensory signals generated during the eating process—from smell, taste, and gastrointestinal stretch. Senses, perception of nutrients, etc., are integrated and transformed into dynamic behavioral control.
In this process, the nucleus of the solitary tract (NTS) located in the brainstem is the first stop for the brain to perceive and integrate eating-related signals, and is crucial for us to feel full. The vagus nerve, which controls the gastrointestinal tract and detects gastrointestinal stretch, transmits signals directly here to activate related nerve cells.
However, due to technical limitations in the past, scientists could only observe these nerve cells in anesthetized animals or brain slices. They were unable to directly record the activity changes of these cells when the animals were awake. Therefore, it was difficult to know how the brain based on sensation and control during eating. Feedback from locomotion processes satiety signals, as well as how other types of feeding signals outside the gastrointestinal tract affect an animal's appetite.
In this new study, a team led by Professor Zachary Knight developed a new technology that, for the first time, was able to image and record different types of neurons in the nucleus tractus solitarius when mice were awake and active.
They observed that when liquid nutrition solution was delivered directly into the stomach of mice, a type of PRLH neurons (prolactin-releasing hormone) in the nucleus of the solitary tract were continuously activated by nutritional signals from the digestive tract within tens of minutes. This This is consistent with conventional wisdom and previous research results.
However, when the researchers let the mice eat and drink as usual, they found that the signal from the intestine did not appear, and the PRLH nerve changed to a new activity pattern: completely controlled by oral signals, related to how long it took to eat and the taste of the food. When mice first start licking nutrient solution or high-fat food, PRLH neurons are rapidly activated within a few seconds; once they stop licking, neural activity also stops quickly.
In the experiment, the researchers also used lasers to artificially activate PRLH neurons in mice and found that this allowed them to slow down their eating speed. But if these mice lose the ability to taste tastes such as sweetness in advance, PRLH neurons cannot be activated during eating. These results suggest that PRLH neurons that slow down an animal's eating need to be activated by the taste of food.
In the words of the researchers, the brain uses the sense of taste to make two judgments at the same time. One is saying "eat more if it tastes good", and the other is saying "eat slowly, don't eat too fast". In other words, taste is the first line of defense to avoid eating too fast and eating too much. Only by chewing slowly and slowly can this line of defense be fully utilized.
At the same time, the researchers also looked at another group of CGC neurons in the nucleus tractus solitarius and found that they only responded to signals from the gastrointestinal tract, but these cells responded much slower and lasted longer. More, can suppress hunger for a longer period of time.
Taken together, these two sets of neurons in the brainstem control how fast and how much we eat, ultimately making us feel less hungry and full.
These findings bring new inspiration for how to regulate appetite and effectively lose weight. For example, the "star weight loss drug" semaglutide imitates the hormone released by CGC cells after receiving intestinal stretching signals. The reason why it can achieve amazing weight loss results is inseparable from its appetite suppressing effect. Now, using techniques developed in a new study, researchers say it's possible to further understand how exactly this class of weight-loss drugs works in the brainstem, how signals from different parts of the body control appetite, and how the interactions between signals from two groups of brain cells can be optimized. Interact with each other to design a weight loss program for different eating patterns.