This Environmental Factor May Be Affecting Your Gut-Brain Connection
You know that heavy, wiped-out feeling after too long outside on a really hot day.
You're thirsty, a little foggy, and your appetite may feel off, too.
Heat is genuinely hard on the body, and researchers are starting to look at what it may be doing further below the surface.
In a new review1, researchers looked at how heat may affect your gut and your brain together, and whether some of the effects of extreme heat start in the gut before you notice them anywhere else.
About the review
Researchers pulled together what's already known about heat and the microbiota-gut-brain axis, the two-way line of communication that runs between your gut bacteria and your brain.
They also looked at what might help protect the gut when it's hot.
That axis works through nerves, immune signals, and chemicals made in the body, which keeps your gut and brain in constant communication. The bacteria living in your gut are part of the conversation, so what happens down there can affect more than digestion, including your stress response.
One thing to know up front: most of the studies in the review were done in animals, including mice, rabbits, chickens, goats, pigs, and cows. There's much less human research, so the review is better at explaining what might be going on than proving it happens in people.
What heat may be doing inside the gut
In the animal studies, heat changed the mix of bacteria in the gut. Which bacteria shifted depended on the animal, but the pattern kept showing up.
Heat may also loosen the gut lining, which normally keeps bacteria and their byproducts inside the digestive tract.
When more of those substances slip into the bloodstream, the body tends to respond with inflammation, and that inflammation may change the messages traveling along the microbiota-gut-brain axis.
Many of those messages move along the vagus nerve, a long nerve running between your gut and your brain.
Put simply, the proposed sequence is this. Heat shifts your gut bacteria, the gut lining gets a little leakier, inflammation follows, and gut-brain messaging may get thrown off.
The human evidence is still pretty limited
This is where it pays not to run ahead of the science.
The review points to one human study that compared people who had gotten sick from heat while exercising with a similar-sized group who hadn't.
Researchers didn't find big differences between the two groups in their gut bacteria, gut lining function, or inflammation.
There was one difference. People who didn't handle heat well had less of one major group of gut bacteria (Firmicutes) compared with another (Bacteroidota).
But that alone doesn't tell us heat caused the shift, and more human research is needed.
What you can do when it's hot out
The review covers a few microbiome strategies scientists are testing, including probiotics, prebiotics, synbiotics, and postbiotic compounds, which are the helpful byproducts your gut bacteria make.
The evidence for using any of them specifically for heat-related gut changes is still early, especially in people.
You don't need a special hot-weather gut routine, though, because the habits that support your gut the rest of the year still apply when temperatures climb.
- Fill up on fiber-rich foods: They feed the helpful bacteria living in your gut.
- Add fermented foods: Work them in if they sit well with you.
- Drink enough water: Especially on days you're sweating more than usual.
- Think about whether a probiotic fits your routine: That's a bigger gut health question than heat alone.
The review also mentions stool transplants and targeted compounds made by gut bacteria as possible options down the road. Those are research topics, not something to try at home.
The takeaway
Heat may shift your gut bacteria and nudge the systems that let your gut and brain talk to each other, but most of what we know so far comes from animals.
Staying hydrated and eating in a way that supports your gut are still smart moves while researchers sort out what this means for people.