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Dietary Considerations in Autism Spectrum Disorders: The Potential Role of Protein Digestion and Microbial Putrefaction in the Gut-Brain Axis


Dietary Considerations in Autism Spectrum Disorders: The Potential Role of Protein Digestion and Microbial Putrefaction in the Gut-Brain Axis

Megan R Sanctuary et al. Front Nutr.


Children with autism spectrum disorders (ASD), characterized by a range of behavioral abnormalities and social deficits, display high incidence of gastrointestinal (GI) co-morbidities including chronic constipation and diarrhea. Research is now increasingly able to characterize the "fragile gut" in these children and understand the role that impairment of specific GI functions plays in the GI symptoms associated with ASD. This mechanistic understanding is extending to the interactions between diet and ASD, including food structure and protein digestive capacity in exacerbating autistic symptoms. Children with ASD and gut co-morbidities exhibit low digestive enzyme activity, impaired gut barrier integrity and the presence of antibodies specific for dietary proteins in the peripheral circulation. These findings support the hypothesis that entry of dietary peptides from the gut lumen into the vasculature are associated with an aberrant immune response. Furthermore, a subset of children with ASD exhibit high concentrations of metabolites originating from microbial activity on proteinaceous substrates. Taken together, the combination of specific protein intakes poor digestion, gut barrier integrity, microbiota composition and function all on a background of ASD represents a phenotypic pattern. A potential consequence of this pattern of conditions is that the fragile gut of some children with ASD is at risk for GI symptoms that may be amenable to improvement with specific dietary changes. There is growing evidence that shows an association between gut dysfunction and dysbiosis and ASD symptoms. It is therefore urgent to perform more experimental and clinical research on the "fragile gut" in children with ASD in order to move toward advancements in clinical practice. Identifying those factors that are of clinical value will provide an evidence-based path to individual management and targeted solutions; from real time sensing to the design of diets with personalized protein source/processing, all to improve GI function in children with ASD.

Keywords: constipation; diarrhea; dietary protein; fragile gut; gastrointestinal; gut-brain; microbiota; probiotics.


Figure 1
Figure 1
Robust vs. Fragile Gut Function in Children with ASD. (A) Robust Gut: the healthy gut displays robust digestion of proteins and simple sugars by the small intestine brush border enzymes that make these nutrients absorbable. After digestion, very few intact nutrients remain and indigestible polysaccharides (fiber) remain. This fiber is consumed by saccharolytic bacteria, which line most of the large intestine, and produce beneficial byproducts (such as short chain fatty acids). Undigested proteins or amino acids are consumed by putrefactive bacteria, which are few in number, and produce potentially harmful putrefactive metabolites that are easily detoxified. The blood and lymphatics in the villi do not directly interact with the lumen of the small intestine, preventing the interaction of antigenic food molecules with the underlying immune tissue. (B) Fragile Gut: the fragile gut of children with autism displays reduced digestive capacity. The inflammation and deterioration of the gut lining may cause reduced expression and activity of brush border disaccharidases and peptidases and greater amounts of intact simple sugars and proteinaceous substrates and less fermentable fiber. This proteinaceous substrate is consumed by the more prevalent putrefactive bacteria producing greater amounts of putrefactive metabolites, such as ammonia, phenols, and sulfides. The blood and lymphatics in the villi are in contact with the lumen due to the excessive inflammation and the undigested proteins in the intestine are able to directly pass. This process allows for interaction of antigenic proteins with immune tissue leading to an aberrant immune response and subsequent autoantibody production.

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