Probiotics, prebiotics, synbiotics, and fecal microbiota transplantation in the treatment of behavioral symptoms of autism spectrum disorder: A systematic review.
Hold off recommending probiotics or fecal transplants for autism behaviors—current human proof is too weak.
01Research in Context
What this study did
The team looked at every paper that tested probiotics, prebiotics, synbiotics, or fecal transplants for autism behaviors.
They only kept studies with human kids or adults. No animal tests counted.
After they pulled the papers apart, they said the proof is still too thin to tell parents to use these products.
What they found
Most trials were tiny and short. Many had no control group.
Because of that mess, the review says we cannot claim these gut fixes help autism behaviors.
Bottom line: wait for bigger, longer studies before you bet on bugs.
How this fits with other research
Lu et al. (2025) looked at almost the same pile of studies but asked a different question. They found the same treatments do cut tummy pain and boost good Bifidobacterium. So the pills may calm the gut even if they do not touch hand-flapping or eye contact.
Golbaghi et al. (2024) narrowed the lens to mice and rats. Those animal papers hint probiotics can lower brain inflammation. That lab work keeps the idea alive, but it does not overrule the human review.
Nevin et al. (2005) warned us almost twenty years ago that GI-autism links were shaky. Tan et al. (2021) echo that caution with fresher data. The story has not flipped; it just got more detailed.
Why it matters
When a parent asks about probiotic yogurt or pricey stool capsules, you can give a clear answer: “No solid proof for behavior change yet, but it might help stomach pain.” Keep an eye on upcoming trials, and stick to evidence-based skills teaching for now.
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02At a glance
03Original abstract
The emerging role of a microbiota-gut-brain axis in autism spectrum disorder (ASD) suggests that modulating gut microbial composition may offer a tractable approach to addressing the lifelong challenges of ASD. The aim of this systematic review was to provide an overview and critically evaluate the current evidence on the efficacy and safety of probiotic, prebiotic, synbiotic, and fecal microbiota transplantation therapies for core and co-occurring behavioral symptoms in individuals with ASD. Comprehensive searches of MEDLINE, EMBASE, Scopus, Web of Science Core Collection, Cochrane Library, and Google Scholar were performed from inception to March 5, 2020, and two update searches were completed on October 25, 2020, and April 22, 2021, respectively. A total of 4306 publications were identified, of which 14 articles met the inclusion criteria. Data were extracted independently by two reviewers using a preconstructed form. Results of probiotic studies do not confirm the supposed beneficial effect of probiotics on ASD, whereas prebiotics and synbiotic combinations appear to be efficacious in selective behavioral symptoms. Evidence of the efficacy of fecal microbiota transplantation in ASD is still scarce but supports further research. Overall, the current evidence base to suggest beneficial effects of these modalities in ASD is limited and inconclusive. More clinical trials are currently looking at the use of microbial-based therapies in ASD. With a robust double-blind randomized controlled protocol to investigate the efficacy, these trials should provide significant and definitive results. LAY SUMMARY: There is a link between altered gut bacteria and autism spectrum disorder. Some people believe that modulating bacterial composition in the gut may help reduce autism symptoms, but evidence from human studies suggesting beneficial effects of probiotic, prebiotic, and combination thereof as well as fecal transplants in autism spectrum disorder is limited and inconclusive. Current data should not encourage use of these modalities. Further clinical studies are needed.
Autism research : official journal of the International Society for Autism Research, 2021 · doi:10.1002/aur.2560