Butyrate, the Gut-Brain Axis and What It Means for IBS and Autism

I first learned about butyrate years ago, when my mom was sick with cancer and I was doing my own research. It’s a small molecule your gut bacteria make out of fiber, and it matters well beyond the gut.

This post is what I’ve learned so far, with links to the research so you can read it yourself. I’m not a doctor, and none of this is medical advice.

What butyrate is

Butyrate, or butyric acid, is a short-chain fatty acid. The bacteria in your colon make it when they ferment fiber your body can’t digest on its own, along with two others, acetate and propionate. There’s a little in butter too, which is where the name comes from.

How much you make depends on the state of your gut. A healthy gut, fed plenty of fiber and full of the right bacteria, makes a lot of it. Sick guts tend to make less: people with Crohn’s disease and ulcerative colitis have fewer of the main butyrate makers, like Faecalibacterium prausnitzii, a bacterium that also calms inflammation in the gut. Low-fiber diets, the typical Western diet included, starve those bacteria, and they make less.

The cells that line your colon run on it. Burning butyrate supplies 70 to 80% of the energy healthy colon cells need. It also helps keep the gut lining tight, so less of what’s in your gut leaks where it shouldn’t, and it calms inflammation.

As a supplement it comes as sodium butyrate, calcium or magnesium butyrate, or tributyrin. The good ones are coated so they reach the colon instead of being absorbed early. Fair warning: butyric acid stinks. To me it smells like rancid eggs or farts, which is why the coated capsules exist.

The gut-brain axis

Your gut and your brain talk to each other constantly, through the vagus nerve, the immune system, hormones and the chemicals your gut bacteria make. Researchers call it the gut-brain axis, and short-chain fatty acids like butyrate are one of the main ways the bacteria take part in that conversation.

In one mouse study, mice raised with no gut bacteria at all had immature, poorly working microglia, the brain’s own immune cells. Giving them short-chain fatty acids in their drinking water brought their microglia back to normal. What the bacteria make shapes the brain’s immune system. One review of butyrate went as far as calling it “the bread and butter of the microbiota-gut-brain axis”.

Butyrate and IBS

The human research is strongest here. In a randomized, placebo-controlled trial, 66 adults with IBS took 300 mg a day of coated sodium butyrate alongside their usual treatment. After four weeks, the butyrate group had significantly less abdominal pain during bowel movements.

A Polish study of 3,000 people with IBS taking 150 mg of sodium butyrate twice a day for 12 weeks reported less pain, bloating, diarrhea, constipation and urgency, and almost 94% said they’d keep taking it.

A randomized, placebo-controlled trial in 51 children and teens with IBS gave a daily tablet of 500 mg calcium butyrate (with zinc and vitamin D) for eight weeks. 73% of the butyrate group cut their pain at least in half, against under 4% on placebo, with no side effects reported.

Those are small studies, but they point the same way, and butyrate is cheap and well tolerated.

Autism and the gut

Children with autism are far more likely to have stomach problems. A review of 15 studies found they were about four times as likely to have gut problems in general, and two to three times as likely to have constipation, diarrhea or stomach pain, as other kids. In one study of 176 young children with autism, 93% had at least one gut symptom, and the worse those symptoms were, the more irritability, aggression and repetitive behavior the children had.

A child who can’t say “my stomach hurts” still feels it, and the pain can come out as a meltdown. Nobody has proven that link step by step, but anyone who has cared for a nonverbal child knows how much of their behavior is them trying to tell you something.

Butyrate comes into this from a few directions:

• One study found children with autism had less butyrate in their stool and fewer of the bacteria that make it, especially the ones with constipation. Other studies have found different results, so this isn’t settled.
• In a mouse model of autism, sodium butyrate improved social behavior and shifted brain genes toward calmer, more inhibited signaling. That’s mice, not kids, but it’s a direct look at butyrate and behavior.
• When researchers rebuilt the gut bacteria of 18 children with autism and serious gut problems, their gut symptoms dropped about 80% and their behavior improved. Two years later, most of the gut improvement had held and the autism symptoms had kept improving. That wasn’t butyrate itself, and there was no placebo group, but it shows how much fixing the gut can change.

The trial to watch is happening right now in Italy. It’s giving sodium butyrate or a placebo to 128 children aged 3 to 6 with autism and gut problems for 16 weeks, and alongside their gut symptoms it’s measuring unexplained daytime irritability, sleep and behavior. It’s the first proper test of exactly this question, and it’s due to finish in late 2026.

Getting more of it

The cheapest way to get more butyrate is to feed the bacteria that make it. They live on fiber, especially:

• Oats, barley, beans and lentils.
• Resistant starch: potatoes and rice that have been cooked and cooled, and slightly green bananas.
• Onions, garlic, leeks and asparagus.

Supplements are the more direct route, and most of the studies above used them. If you’re thinking about butyrate for yourself, and especially for a child, talk to a doctor first. Sodium butyrate also adds sodium, which matters for anyone watching their salt.

If you’ve tried butyrate yourself, or for someone you care for, I’d like to hear how it went. My contact page is always open.