It is well known that the gut microbiome (gut microbiota), known as the "second brain," is the largest ecosystem in the body and has co-evolved a very complex relationship with us. A growing body of research confirms that they have a range of far-reaching effects on health, from psychological to physiological: either for health or for health.
Compounds released by gut bacteria are found in the bloodstream and can regulate host physiological processes such as immunity, metabolism, and brain function. This series of operations is achieved through the "gut-brain axis".
On April 16, 2022, a new study published in Science demonstrated the astonishing fact that gut bacteria have a direct dialogue with the brain, and neurons can directly sense the bacteria and adjust appetite and body temperature control accordingly.
Implicitly, our physiology and behavior may be dominated by these invisible "little devils."
Today, let's continue to strike iron while it's hot.
Everyone knows that impulses are the devil, and the impulses that cause you to want to eat a certain food, and the impulses that know that it is junk food but still can't stop it, may be these "little ghosts" in the stomach. So, whether to eat healthy fruits and vegetables + whole wheat bread, or eat the "milk tea + Big Mac" that makes you fatter, we may be at the mercy of intestinal bacteria.
In a new study published in the Proceedings of the National Academy of Sciences (PNAS) on April 19, 2022, two scientists from the Department of Biological Sciences at the University of Pittsburgh in the United States showed for the first time that an animal's gut microbiota influences its food choices when it comes to what diet to eat.
Proper nutrients are essential to life, so animals, including humans, have evolved complex internal sensory systems that help maintain nutrient homeostasis by regulating macronutrient intake. Although the mechanisms are complex, the availability of essential nutrients strongly influences dietary choice behavior.
Because the gut microbiota has been shown to metabolize the same essential nutrients, for decades, scientists thought that the gut microbiota may also be influencing the host's dietary preferences. However, this bold hypothesis has only been tested in small fruit flies and has not been investigated in larger and more similar animals to humans.
In the new study, the two scientists selected three groups of rodents with different dietary habits as microbial donors for lab-free mice that lack gut microbiota. They are 10 carnivores (Onychomys torridus), 10 omnivore white-footed rats (Peromyscus leucopus), and 10 herbivores (Microtus montanus).
Each group of mice was selected for foods rich in different nutrients. Specifically, mice colonized with herbivorous rat populations voluntarily chose a diet with a higher protein and carbohydrate ratio; mice with omnivorous and carnivorous rat populations chose a diet with a lower protein and carbohydrate ratio. This suggests that the gut microbiota changes their dietary preferences.
This conclusion can be said to echo the "interval" of the Science study. We already know that the second brain (gut) and the first brain can talk directly, and certain molecules produced by digestion act as "middlemen".
However, "middlemen" can be selfish, and they hijack the "gut-brain axis" communication line and change the meaning of the message, thus taking away our dietary choices for "my own use".
Let's illustrate this problem with an example: eating sleepiness.
Many people feel sleepy after eating, and one of the reasons is the tryptophan in our body.
Tryptophan is an essential amino acid that is abundant in cereals and nuts. When tryptophan enters the brain, it converts into serotonin, a signal that triggers a feeling of fullness after a meal. Eventually, it will be converted into melatonin, leaving you feeling drowsy.
However, some gut bacteria also have the ability to produce tryptophan.
In the study, the two scientists found that mice with different gut flora also had different plasma tryptophan levels before choosing different diets, and that mice with higher plasma tryptophan levels had more bacteria in their guts that produced tryptophan. Specifically, the intestinal flora of herbivorous animals produces more tryptophan, which leads to higher levels of serotonin in the host brain, triggers satiety, and restricts eating, thereby reducing carbohydrate intake.
The researchers say this is a compelling piece of evidence, but tryptophan is just one line in a complex chemical communication network. They argue that there may be dozens of signals that affect eating behavior on a daily basis, and that tryptophan produced by gut bacteria may be just one aspect of it. But it does establish a plausible way that gut microbiota can change our choices about food.
Kevin Kohl, corresponding author of the study, said: "Perhaps, what you ate the day before had a greater impact on you than your gut microbiome. We also overlooked many things about humans in our experiments. But it's a question worth thinking about. ”
Extensive previous studies have confirmed that eating healthy foods shapes a healthy gut microbiome. In this way, these "little devils" will have a heart for me, and it will ultimately be beneficial to the health of "me" (me and my gut microbiota).
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