Synbiotics and autism: a novel microbiome-based strategy to improve gut and behavioral health in children with autism spectrum disorder

Staff editor

23.09.2025

A study demonstrates that synbiotic supplementation, alone or combined with GDH, is a safe and effective adjunct therapy for autistic children with DGBI.

What is already known

Alterations in the microbiome–gut–brain axis are linked to autism spectrum disorder (ASD) and are common in children with disorders of gut–brain interaction (DGBI), which often worsen behavior and anxiety. While dietary, probiotic interventions and gut-directed hypnotherapy (GDH) have shown some promise, few well-controlled studies have evaluated the effect of synbiotics—a combination of prebiotics and probiotics—on both gut microbiota and core symptoms of ASD.

What this research adds

A randomized trial investigated the effects of a synbiotic, versus a synbiotic supplement combined with in 36 children diagnosed with ASD. Children treated with synbiotic alone and those treated with synbiotics with GDH, both showed significant improvements in GI symptoms. However, the combined treatment led to greater long-term relief from pain and flatulence and showed significant improvements in behavior and anxiety, which were not observed in the synbiotic-only group, indicating a combined approach may improve the longevity of beneficial outcomes for specific GI symptoms. Stool microbiota analysis also revealed an increase in Bifidobacterium and Dialister in both groups, and a unique increase in Faecalibacterium in the combined group.

Conclusions

This study demonstrates that synbiotic supplementation—alone or combined with GDH—is a safe and effective adjunct therapy for autistic children with DGBI. These findings support the role of microbiome-based interventions as a safe and promising approach to address unmet needs in autism care.

Children with ASD frequently experience DGBI, such as constipation, diarrhea, bloating, and abdominal pain. These gastrointestinal comorbidities are not only common but also correlate with increased anxiety and greater autism symptom severity. Despite this, standard care for autistic children often overlooks GI issues. Mounting evidence suggests that disruptions in the microbiome–gut–brain (MGB) axis may contribute to both gastrointestinal and behavioral symptoms in ASD, although the origin of these microbial changes remains under debate.

Recent studies have explored microbiome-targeted interventions, such as prebiotics, probiotics, and faecal microbiota transplantation (FMT), showing potential for improving both gut and behavioral symptoms. In particular, strains such as Lactobacillus rhamnosus GG, L. plantarum, and Bifidobacterium longum have shown positive effects on gut health, microbiota balance, and anxiety-like behavior. The prebiotic fiber partially hydrolyzed guar gum (PHGG) has also shown efficacy in reducing GI symptoms in both DGBI and autistic individuals. Additionally, GDH has demonstrated success in managing GI-related anxiety in DGBI, although it remains untested in the context of autism.

Mitchell and colleagues conducted a study published in Journal of Autism and Developmental Disorders to evaluate the effectiveness of a synbiotic supplement (containing PHGG and a probiotic mixture of Humiome® L. rhamnosus GG, Humiome® L. plantarum DSM 34532, Humiome® B. lactis DSM 32269 and B. longum DSM 32946) alone versus the same synbiotic combined with GDH in improving gastrointestinal symptoms in autistic children. Moreover, changes in behavior, anxiety, and gut microbiota composition were assessed.

The trial, conducted in Brisbane (Australia) and supported by dsm-firmenich, revealed that synbiotic supplementation, both alone and combined with GDH, is safe and effective in reducing gastrointestinal discomfort in autistic children with comorbid DGBI. Both interventions also led to beneficial shifts in gut microbiota.

Improvements of gastrointestinal outcomes following treatment

A total of 36 children were randomly assigned to the trial (18 in the synbiotic treatment group, SYN group, and 18 in the combined treatment group, synbiotic + GDH, COM group). The intervention period lasted 12 weeks with an additional 12-week follow-up. Both the SYN group and the COM group experienced statistically and clinically significant reductions in gastrointestinal symptom severity over the 12-week intervention period. These improvements were also sustained at the 24-week follow-up, even when controlling for sex, baseline anxiety levels, and antibiotic exposure.

Further analysis revealed significant improvements in both groups for pain and stool smell after 12 weeks. The SYN group also showed a significant reduction in diarrhea frequency and improved stool consistency, whereas the COM group demonstrated a significant reduction in flatulence.

Notably, at follow-up, only the COM group maintained the improvements observed in pain and flatulence, suggesting that while both interventions were effective in the short term, the addition of GDH may help sustain certain GI symptom improvements over time.

Other Gut-Based Outcomes

After 12 weeks, 73% of participants in the COM group showed improvements in stool consistency, compared to 50% in the SYN group. Similarly, a higher proportion of participants in the COM group were classified as “responders” post-intervention (75%) compared to the SYN group (66.7%). This trend persisted at the 24-week follow-up, with 90.9% of the COM group and 63.6% of the SYN group classified as responders. While these findings were not statistically significant, they suggest a possible clinical advantage of the combined intervention in improving stool-related outcomes.

Treatment effects on behaviour and anxiety

Following the 12-week intervention, the COM group showed statistically and clinically significant improvements in behavior and anxiety. Notably, children in this group were less irritable, more cooperative, and less socially withdrawn. Their anxiety levels also dropped significantly.

In contrast, the SYN group showed some improvement, mainly in social behavior and hyperactivity, with hyperactivity being the only change that was also clinically meaningful. There was a slight improvement in irritability, but it wasn’t strong enough to be considered significant. Anxiety levels in the SYN group did not change. Overall, these results suggest that combining the synbiotic with hypnotherapy had a greater and wider effect on behavior and anxiety.

Changes in microbiome composition

Analysis of the stool microbiome revealed changes in microbial composition following the 12-week intervention. Both groups experienced a significant rise in Bifidobacterium animalis and Dialister, whereas the COM group showed increases in Faecalibacterium, a strain linked to gut health and lower anxiety levels. These findings suggest that both interventions led to beneficial and distinct microbial shifts associated with improved gut health.

The present study is the first to evaluate a combined gut-brain approach—oral synbiotic supplementation paired with GDH—in autistic children with disorders of DGBI. While both the synbiotic-only and combined interventions were safe and significantly reduced gastrointestinal symptoms, the COM group exhibited added benefits. Notably, behavioural improvements are clinically relevant given the bi-directional relationship between anxiety, irritability, and GI symptoms in autistic individuals. The study supports the emerging view that targeting the microbiome may help modulate brain function and behavior in neurodevelopmental conditions. While more research is needed to replicate these findings in larger and more diverse populations, synbiotics could become part of an integrated therapeutic approach for ASD—one that addresses not only the brain but the gut as a therapeutic gateway.

Source

Journal of Autism and Developmental Disorders

Content sponsored by

dsm-firmenich is a global leader in science-backed health, nutrition, and biosciences. Beyond traditional vitamins, the company is driving innovation with Biotic Vitamins, Human Milk Oligosaccharides ...

dsm-firmenich is part of