Clinical data availableGut-brain axis365 patients

Autism Spectrum Disorder

A key focus area at Han's United. With data from 365 patients, we have accumulated extensive clinical experience applying FMT for autism spectrum disorder. 90% of serotonin is produced in the gut — the link between the microbiome and the brain is proven.

For parents: We understand how important it is to find effective help for your child. Our approach is based on scientific evidence and individualized care for every family.

Reviewed by:Dr. Zhang Wei·Gastroenterologist, Han's UnitedUpdated:March 12, 2026

What is ASD?

Autism Spectrum Disorder — a group of neurodevelopmental conditions affecting communication, behavior, and social interaction.

About the condition

ASD affects approximately 1 in 36 children. It is a spectrum of conditions with varying degrees of symptom severity. Diagnosis is based on behavioral criteria.

Important: 40–90% of children with ASD have GI problems — significantly more than in the general population. Treating GI issues can substantially improve behavior and quality of life.

GI symptoms in ASD

Chronic constipation or diarrhea
Abdominal pain and bloating
Selective eating, bad breath
Sleep disturbances related to GI discomfort
Altered microbiome composition

The microbiome-gut-brain axis

90% of serotonin is produced in the gut, not in the brain
Bacteria produce GABA, short-chain fatty acids
The vagus nerve directly connects the gut and the brain
Dysbiosis is linked to inflammation and neuroinflammation

Conventional approaches

Include behavioral therapy, speech therapy, occupational therapy, and special diets. GI symptoms are often overlooked.

GI problems can exacerbate behavioral symptoms, creating a vicious cycle of discomfort and stress. Many "unusual" movements are actually attempts to relieve abdominal pain.

For parents

The gut-brain connection in children

Imagine your child's body as a big house. The brain is the owner on the top floor. The gut is the kitchen and boiler room in the basement. Problems "upstairs" often start "downstairs."

"A direct phone line"

Between the belly and the head runs a thick "cable" — the vagus nerve. They communicate around the clock.

If there's a storm in the belly — gas, bloating, or constipation — the gut is constantly "calling" the brain: "We have an emergency!" The brain can't focus on learning, speaking, or playing. The child becomes anxious, fearful, and meltdowns happen.

"The calm factory"

Happy hormones are produced not in the head, but in the belly. 90% of serotonin comes from the gut.

Beneficial bacteria work like tiny cooks — preparing "joy vitamins." If a child has harmful bacteria, the cooks aren't working. The brain has nothing to run on. The child becomes tearful, lethargic, or conversely, overly agitated.

"A dirty filter" (Brain fog)

A healthy gut is a tight filter. In many children with autism, this filter is inflamed — like a sieve with large holes.

Toxins enter the bloodstream and go straight to the brain. The brain gets mildly poisoned. Imagine how you feel with the flu: foggy head, light is irritating. The child withdraws, stops making eye contact, or runs in circles.

"Pain that can't be expressed"

The most important point for parents of non-verbal children.

Imagine having a severe stomachache. And someone asks you to solve a puzzle. Many "unusual" movements (hitting the belly, pressing against the corner of a sofa) are attempts to relieve pain. When we treat the gut — the pain goes away, and the "problem" behavior disappears.

Key takeaway for parents

When you treat the gut, you accomplish three things:

1. Stop "poisoning" the brain

The fog clears, the child thinks more clearly

2. Give the brain fuel

The child becomes calmer

3. Remove the pain

Meltdowns stop

Why FMT for autism?

Restoring a healthy microbiome improves both GI symptoms and behavioral manifestations. A course of 6–10 transplantations provides a sustained clinical effect.

Dysbiosis in ASD

Reduced diversity, pathogen overgrowth

GI and neuroinflammation

Intestinal permeability, inflammatory signals

FMT course (6–10 procedures)

Donor material from healthy children of mountainous regions

Sustained improvement

GI, sleep, behavior, socialization

Mechanism of action

FMT restores microbiome balance, reduces intestinal inflammation, normalizes production of serotonin, GABA, and short-chain fatty acids, and improves intestinal barrier function.

Observed improvements

Normalized GI function (constipation, diarrhea, pain)
Improved sleep and emotional stability
Reduced irritability and self-injurious behavior
Improved communication and socialization

Results: our data and global research

Han's United holds one of the largest databases on FMT use for autism. Global research confirms our clinical experience.

365

ASD patients in the Han's United database

75.3%

Improvement in a group of 365 patients (3 months)

80%

GI symptom reduction (Kang et al.)

2 years+

Effect sustained in studies

Key studies and data

Han's United (cohort of 365 patients): Clinical improvement at 3 months in 75.3% (275 out of 365 ASD patients)
Kang et al., Microbiome 2017: MTT (modified FMT) improved GI symptoms by 80% and behavioral scores in children with ASD
Kang et al., Scientific Reports 2019: Two-year follow-up: effects persist, behavioral improvements continue to grow
Prof. Yang Guan: Leading expert in microbiota and autism, research on the gut-brain connection