PNAS: What do you want to eat, it may just be your gut flora wanting to eat

Written | Edited by Wang Cong | Typeset by Wang Duoyu | Shui Chengwen Humans, like other mammals, have their bodies populated by trillions of microbes, including bacteria, viruses and fungi, collectively known as symbiotic flora
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In a sense, "human" is a multi-complex composed of human body and symbiotic flora
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A large number of microorganisms are parasitized in the human gut.
These gut microbiomes affect human obesity, enteritis, autoimmune diseases, response to cancer treatment drugs, and even affect human lifespan
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Growing evidence has revealed the extent of interdependence between humans and these gut microbiomes, emphasizing the importance of the brain-gut axis
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We often have a thought in our minds, such as suddenly wanting to eat meat, suddenly wanting to drink milk tea and so on
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Even where you come from, scientists have long speculated that gut microbes influence a person's dietary choices and preferences, but that speculation hasn't been well-studied
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On April 19, 2022, researchers from the University of Pittsburgh published a research paper titled: The gut microbiome influences host diet selection behavior in the Proceedings of the National Academy of Sciences (PNAS)
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The study found that gut microbes influence the host's food choices by producing substances that crave different types of food
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That said, your dietary choices may not be entirely yours, and gut microbes are also involved
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For this study, the research team selected three different mice - locust-eating rats (O.
torridus), white-footed rats (P.
leucopus), and mountain voles (M.
montanus), which have very different eating habits, carnivorous, omnivorous, herbivorous
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Their gut microbes were then individually transplanted into 10 mice lacking gut microbes
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The results showed that the mice's dietary preferences changed after the gut microbe transplant
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Specifically, mice transplanted with herbivorous gut microbes chose foods with a higher protein:carb ratio, while mice transplanted with omnivorous and carnivorous gut microbes chose lower protein : Foods with a carbohydrate ratio
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It may sound far-fetched that gut microbes influence host behavior, but it's actually not surprising
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There is a constant "conversation" between the gut and the brain, such as some metabolites produced during eating that make you feel full and stop eating
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And gut microbes can also produce the same metabolites, so they may also "talk" to the brain
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On April 15, 2022, a research team from the Pasteur Institute in France published a paper in the journal Science showing that neurons in the hypothalamus can directly sense changes in gut bacterial activity and adjust appetite and body temperature accordingly
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This suggests a direct dialogue between the gut microbiome and the brain
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In this PNAS paper, the research team noted that the drowsy feeling that occurs after eating turkey or drinking milk is due to the fact that they are rich in tryptophan, an essential amino acid that enters the brain and is converted into Serotonin, which makes people feel full, is eventually converted into melatonin, which makes people sleepy and promotes sleep
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And gut microbes can also produce tryptophan.
The study found that mice with different gut microbiomes had different levels of tryptophan in their blood, even before they were allowed to freely choose their food.

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Those mice with higher levels of tryptophan in their blood also had more tryptophan-producing bacteria in their guts
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Specifically, the gut microbes of herbivores produce more tryptophan, which in turn causes the host's brain to produce more serotonin, limiting the host's feeding and reducing carbohydrate intake
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Brian K.
Trevelline, the corresponding author of the paper, said that this study provides a convincing and conclusive evidence that gut microbes can regulate the host's dietary choices by producing tryptophan, providing a theoretical conjecture that microbes change dietary choices.
A rigorous experimental verification was carried out
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But he also noted that there may be dozens of signals that influence dietary choices, and microbial production of tryptophan is just one of them
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In humans, for example, what you ate the day before was important to what you choose to eat today, and this effect may be greater than the effect of gut microbes
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