A Meta-analysis of Gut Microbiota in Children with Autism.

Andreo-Martínez et al. (2022) pooled 18 earlier studies that sequenced gut bacteria in kids with autism. They compared the microbial mix to typically developing peers. The goal was to see which bugs, if any, reliably differ.

Two bacteria showed up less often in autistic children: Streptococcus and Bifidobacterium. The drop was seen across most studies, but the data were messy and some papers had bias. So the authors call the finding suggestive, not proven.

Lu et al. (2025) extends this picture. They looked at 19 probiotic or synbiotic trials and found giving kids these supplements raised Bifidobacterium back toward normal and also eased tummy pain. The same bug Pedro found missing is the one probiotics boost.

Mouridsen et al. (2013) seems to disagree. A Danish registry saw no extra GI disease in adults who had childhood autism. The key gap: Erik counted hospital diagnoses, not microbial counts. Microbes can shift without full-blown disease, so both papers can be true.

Tan et al. (2021) came just before Pedro. They scoured probiotic studies for behavior change and ruled the evidence too weak. Pedro stays neutral on behavior; together the pair shows the microbial signal is clearer than the clinical payoff—for now.

You now have a concrete microbial target: low Bifidobacterium. If a client has GI pain plus autism, a probiotic with this strain is worth discussing with the pediatrician. Track stool and behavior for eight weeks; Hsuan-Hsuan’s meta says that is the minimum window for benefit. Keep expectations modest—microbes may move more than moods.