Does your gut really talk to your brain, and do microbes join the conversation?
Your gut has its own mesh of neurons, and 90% of your serotonin is there. Whether your microbes influence your mood is a much shakier claim.
▶ Start the storyYes, your gut and brain talk to each other, but whether your microbes join the conversation in a way that matters for mood is still preliminary. The gut–brain axis is two-way biochemical signalling between the gastrointestinal tract and the central nervous system. The "microbiota–gut–brain axis" adds the putative role of gut microbes interacting with brain functions, according to preliminary research.
The solid part is the nerves. The , a mesh of neurons that governs the digestive system, has been described as a "second brain", and it keeps working even when the to the brain is severed. More than 90 percent of the body's lies in the gut, as does about 50 percent of its dopamine. The oldest known example of the link is the one Pavlov demonstrated in 1904: the smell and sight of food trigger gastric and pancreatic secretions.
The microbial part rests on a different type of evidence. Interest was sparked by a 2004 study in which showed an exaggerated stress-hormone response compared with ordinary lab mice. Gut microbes can produce neuroactive molecules such as acetylcholine, histamine, melatonin and , and they release molecules that can directly activate the .
Well established
- The gut has its own mesh of neurons, the
- More than 90% of the body's is in the gut
- Smell and sight of food trigger gut secretions (Pavlov, 1904)
Preliminary
- Gut microbes shaping mood and brain function
- Mostly animal studies, including
- Human links are , not causal
Now the careful bit. Most of the work on microbes in the gut–brain axis has been done in animals, including highly artificial . Human studies, as of 2016, were generally small and could not be generalised, and it remains unclear whether changes in microbes are a result of disease, a cause of it, or both. Links with depression, anxiety and bipolar disorder come mostly from animals and small human groups, and the current literature considers them and not causal.
So the honest answer is yes to the conversation, and "not yet proven" to the microbes' role in mood.
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Recap
The gut and brain definitely signal to each other, but a causal role for gut microbes in mood or mental health is not yet shown in humans.
💡 A trick to remember it · The gut's own nerves are a proven phone line; the microbes' voice on that line is still a rumour being checked.
Surprising fact · The gut has its own neurons and holds over 90% of the body's serotonin, but links from microbes to mood are mostly correlational.
Connects to
- 🧬 How do scientists read a whole microbial community from one gene?
- 🥛 What does the evidence really say about probiotics?
- 🫀 Why does one nerve run from your brainstem all the way to your gut?
- 🦟 Why did medieval Europeans believe having lice was a sign you were healthy?
- 🦠 What do the trillions of microbes in your gut actually do?
- Serotonin
Sources (1)
No source, no claim. Every fact in this lesson (15 claims) cites at least one of these.