The interaction between diet and gut bacteria in Autism Spectrum Disorder
The gastrointestinal tract is inhabited by millions of bacteria that live in a symbiont relationship with the human host. In recent years, researchers have discovered more and more that the gut bacteria can have effects on the host’s behavior and mental process.
Increasing reports are published describing the difference in gut bacteria composition of individuals with behavioral disorders, including Autism Spectrum Disorders (ASD). However, results of the studies are not always consistent so not one clear trend is emerging yet.
Moreover, in children with ASD, differences in bacterial products have been found. Bacteria can use undigested food (i.e., dietary fiber) to create products (bacterial metabolites) that can be absorbed and used by the human host. For example, fermentation of undigested carbohydrates like dietary fiber can be used by the gut bacteria to produce so called short chain fatty acids (i.e., acetate, propionate, butyrate). Using animal models, one of these fatty acids, propionate, has been hypothesized to contribute to some symptoms of ASD. Strategies to manipulate the gut bacteria as a therapeutic potential (e.g., probiotic/prebiotics) showed some improvement in symptom severity, further suggesting that the gut bacteria could impact the behavior of individuals with ASD.
Children with ASD are often very picky eaters. Almost 90% of children with ASD experience some kind of feeding related concern which could be due to food allergies, digestive problems or problematic eating behaviors. Because of these difficult eating behaviors, deficiencies in some nutrients were observed in children with ASD. Some nutrition intervention studies (e.g., gluten-free/casein-free) have explored the potential of diet to manage some symptoms of ASD with limited success
Mechanisms underlying the cross-talk between the gut bacteria and behavior of children with ASD is currently in its infancy. Some studies suggest that effects on the brain can come directly through the bacteria, through bacterial products which translocate into the blood stream, through activation of receptors that send signals to the brain, or through activation of the immune system by components present on bacteria itself (e.g., lipopolysaccharides) (Fig. 1). Because diet and gut bacteria have both independently been shown to have some effect on ASD symptomology and diet is known to be a major environmental factor shaping the composition of the gut bacteria, dietary intake and gut bacteria could potentially act in concert in influencing some symptoms of ASD. Previous studies exploring the gut bacteria in ASD include limited information on the dietary patterns and nutrient intake, so that this connection remains to be explored. Future studies should include detailed dietary histories and food diaries to further understand whether diet has the potential to moderate the effect of the gut bacteria on behavior in children with ASD. New findings could lead to improvements in using diet as a intervention to treat some symptoms of ASD.
Kirsten Berding, Sharon Donovan
Division of Nutritional Sciences, University of Illinois at Urbana-Champaign, USA
Microbiome and nutrition in autism spectrum disorder: current knowledge and research needs.
Berding K, Donovan SM
Nutr Rev. 2016 Dec