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Gut bacteria may be the ‘starter’ of different cravings in humans

When we plan the foods we want to eat every day, the decisions we make may not come from “brain commands”. Now, an experiment on mice at the University of Pittsburgh, USA has shown that the animals’ gut bacteria can influence their dietary choices, with the bacteria producing substances that make them sick. Animals crave certain foods.

Kevin Kohl, an associate professor in the Department of Biology at the University of Pittsburgh, said: “We all have some sort of craving — cravings for salads or cravings for meat, and new research shows that microbes Different gut bacteria in animals may determine their food choices.”

Although scientists have speculated for decades about whether gut bacteria influence our dietary preferences, it was not until recently that the idea was tested in animals. mammal. Kevin Kohl and his colleague Brian Trevelline conducted a special experiment in which 30 mice lacking gut bacteria were injected with a mixture of gut bacteria from three groups of wild-type mice with different diets. .

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The gut microbiome is a complex community of microorganisms that inhabit the digestive tracts of humans and other animals, including insects. The gut polygenomes are the aggregate of all the gut microbiota genomes. The gut is one niche where human microorganisms live.

Kevin found that each group of mice in the experiment had different nutrient-rich food choices, suggesting that the injected gut bacteria changed their previous eating preferences. The findings were recently published in the Proceedings of the National Academy of Sciences of the United States of America.

While the idea that the microbiome affects human behavior sounds far-fetched, scientists have taken a seriously scientific approach. In fact, the human gut and brain are constantly communicating with each other, with certain molecules acting as “mediators”. Digestive by-products in the intestines may indicate that the person has eaten enough food or needs a certain nutrient. At the same time, gut bacteria can produce a number of “middle molecules” that can hijack the initial communication lines of the gut and brain, thereby changing the meaning of the message.

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In humans, the gut microbiota has the largest number of bacteria and the largest number of species compared to other regions of the body. The gut microbiome is established one to two years after human birth, and by that time the intestinal epithelium and the intestinal mucosal barrier it secretes are in a similar way tolerating, and even supporting. support, gut flora and also provide a barrier to pathogenic organisms.

Normally, for people who have ever eaten turkey, their bodies will have a very familiar messenger molecule – tryptophan. Tryptophan is an essential amino acid molecule that is ubiquitous in turkey feed and is also produced by gut bacteria. “When tryptophan gets into the brain, it’s converted to serotonin, an important signal that’s so important for post-meal satisfaction, and it’s eventually converted to melatonin, which makes people feel better,” says Brian Trevelline. feel sleepy”.

In this latest study, Brian and Kevin have shown that mice with different gut microbiomes have different blood levels of tryptophan, and they even choose different foods. At the same time, they found that the higher the blood levels of tryptophan, the more gut bacteria there were.

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The composition of the human gut microbiome changes over time, as dietary changes, and as changes in overall health. A systematic review from 2016 examined preclinical and small human trials that were conducted with several commercially available strains of probiotic bacteria and identified those with the most potential to be useful. for some central nervous system disorders.

Brian Trevelline says this is compelling and conclusive evidence that tryptophan is just one clue in a complex web of chemical communications. There can be dozens of cues that influence everyday eating behavior. Microbial-produced tryptophan may be just one factor, but a plausible explanation, as gut bacteria that can change our dietary choices. Although scientists have been trying to establish and perfect the theory for years, this is just one of a handful of rigorous experiments to prove the gut-brain connection.

“There are many factors that determine people’s dietary choices, and the food eaten the day before may be more important than the gut microbiome,” says Kevin.

He also points out that this may just be a behavior that the microbiome changes that we don’t know about. This is a new area of ​​discovery and there is still a lot of knowledge to be discovered.

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