![Children with autism spectrum disorder (ASD) often experience gastrointestinal (GI) symptoms, which are communicated through non-verbal cues due to their difficulty in expressing discomfort. These cues can be categorized into vocal behaviors (e.g., throat clearing, moaning, sobbing), motor behaviors (e.g., abdominal pressing, pointing, self-injury), aggressive behaviors (e.g., irritability, tantrums), and sleep disturbances (e.g., difficulty falling or staying asleep) [83,84]. Common causes include dysbiosis, gastroesophageal reflux, stomach pain, constipation, and medication side effects [72,82,86]. Early identification of these behaviors is crucial for timely intervention, improving the child’s overall well-being.](https://www.researchgate.net/publication/388508500/figure/fig2/AS:11431281309462786@1739379374162/Children-with-autism-spectrum-disorder-ASD-often-experience-gastrointestinal-GI_Q320.jpg)
![The gut–brain axis is a complex, bidirectional communication network linking the central nervous system (CNS) and the enteric nervous system (ENS), playing a key role in regulating mood, cognition, and overall health. This interaction occurs through four primary pathways: (A) the neural pathway, where the vagus nerve facilitates direct communication between the gut and brain [88]; (B) the endocrine pathway, involving the hypothalamic–pituitary–adrenal (HPA) axis and gut hormones like GLP-1 and PYY to mediate stress responses and regulate appetite [89,90,91]; (C) the immune system pathway, where cytokines and immune cells modulate neuroinflammation and brain function [92,93]; (D) the microbial metabolites pathway, where microbial byproducts like short-chain fatty acids (SCFAs) influence neurotransmitter production and maintain blood–brain barrier integrity [94,95,96,97]. Disruptions in these pathways, such as dysbiosis or increased intestinal permeability, can lead to neuroinflammation, altered neurotransmitter levels, and various neurological or psychiatric disorders [98,99].](https://www.researchgate.net/publication/388508500/figure/fig3/AS:11431281309482117@1739379374950/The-gut-brain-axis-is-a-complex-bidirectional-communication-network-linking-the-central_Q320.jpg)
![Children with ARFID exhibited higher microbial diversity but lower species richness compared to healthy children. Their gut microbiota showed increased levels of potentially harmful bacteria, including Enterobacteriaceae and Bacteroides vulgatus, which have mixed effects on gut health—both reducing inflammation in some contexts and promoting inflammatory bowel disorders in others [36,118,119,120,121]. In contrast, beneficial Bifidobacterium species, known for supporting gut health, were significantly reduced in the ARFID group [122].](https://www.researchgate.net/publication/388508500/figure/fig4/AS:11431281309482118@1739379375537/Children-with-ARFID-exhibited-higher-microbial-diversity-but-lower-species-richness_Q320.jpg)
![A self-perpetuating cycle links ASD symptoms, ARFID development, and gut microbiota degradation. Sensory processing issues in ASD, such as atypical sensory modulation and oral over-sensitivity, drive food selectivity and neophobia, increasing ARFID prevalence [39]. ARFID disrupts gut microbiota, reducing beneficial species like Bifidobacterium and increasing harmful bacteria like Enterobacteriaceae and Bacteroides vulgatus [36]. This dysbiosis affects the gut–brain axis through neural, endocrine, immune, and metabolic pathways, exacerbating ASD symptoms via neuroinflammation, altered neurotransmitter production, and heightened stress responses [97,98,125,126,127].](https://www.researchgate.net/publication/388508500/figure/fig5/AS:11431281309462787@1739379376012/A-self-perpetuating-cycle-links-ASD-symptoms-ARFID-development-and-gut-microbiota_Q320.jpg)
January 2025
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Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by challenges in social communication, restricted interests, and repetitive behaviors. It is also associated with a high prevalence of eating disorders, gastrointestinal (GI) symptoms, and alterations in gut microbiota composition. One of the most pressing concerns is food selectivity. Various eating disorders, such as food neophobia, avoidant/restrictive food intake disorder (ARFID), specific dietary patterns, and poor-quality diets, are commonly observed in this population, often leading to nutrient deficiencies. Additionally, gastrointestinal problems in children with ASD are linked to imbalances in gut microbiota and immune system dysregulation. The aim of this narrative review is to identify previous associations between the gut–brain axis and gastrointestinal problems in ASD. We discuss the impact of the “microbiome–gut–brain axis”, a bidirectional connection between gut microbiota and brain function, on the development and symptoms of ASD. In gastrointestinal problems associated with ASD, a ‘vicious cycle’ may play a significant role: ASD symptoms contribute to the prevalence of ARFID, which in turn leads to microbiota degradation, ultimately worsening ASD symptoms. Current data suggest a link between gastrointestinal problems in ASD and the microbiota, but the amount of evidence is limited. Further research is needed, targeting the correlation of a patient’s microbiota status, dietary habits, and disease course.