Autism spectrum disorder (ASD) is a multifaceted neurological condition with a multitude of emotional, cognitive, behavioral, and physical symptoms that may vary in presentation amongst individuals. These symptoms may be influenced by a variety of internal and external factors, ranging from genetic characteristics to comorbid conditions to home and school environments. Due to its complexity, clinicians, parents, and patients often struggle to find treatment options that effectively address the full spectrum of symptoms. Because conventional treatment such as pharmacological and behavioral interventions often fail to produce complete symptom remission, professionals in the research and clinical communities are increasingly considering the potential benefits of diet-based autism treatment options. Thanks to a growing body of research, there is now evidence that making well-informed, patient-specific dietary decisions can address some of the underlying factors that cause or exacerbate symptoms of autism.
Dietary Choices that Support the Functioning of the Gut-Brain Axis
“Gut-brain axis” has become a major buzzword within the research and medical communities, especially in the context of autism. This term is used to describe the ongoing, bidirectional communication between the Central Nervous System and the components of the enteric nervous system in the gastrointestinal tract. Some of the emotional and cognitive centers in the brain are closely connected to the function of the gastrointestinal system, and communication between the brain and the GI tract is largely facilitated by microbial communities in the gut. Therefore, maintaining a healthy gut microbiome is essential to support the normal functioning of the gut-brain axis. In recent years, growing knowledge of how to modulate the microbiome through dietary interventions have opened up the door to increased treatment possibilities that address a range of autism symptoms.
While supporting the gut microbiome is important for people with a range of health conditions, microbiome-friendly diets are particularly critical for patients with autism due the fact that the gut microbial communities in patients with autism are different from those of their healthy counterparts, compromising gut microbiome health. For instance, multiple studies have revealed lower levels of bacterial diversity (both within and between phyla) in the GI tracts of patients with autism. There are also studies that have specifically shown lower levels of “good” bacteria, like species of Bifidobacterium species, as well as higher levels of bacteria in the Caloramator, Sarcina, and Clostridium genera.
In order to address these discrepancies, patients with autism may be encouraged to choose probiotic-rich foods. Some clinicians are even considering the development of patient-specific probiotic and prebiotic supplementation regimens, which can be tailored to a patient’s needs based on the microbial composition of their GI tract. So far, the evidence on the efficacy of probiotics for improving gastrointestinal and behavioral symptoms of autism is mixed. Some studies suggest possible improvements in both areas, but larger scale trials are needed in the future. There is also early biochemical evidence suggesting that vitamin B12 supplements may be able to modulate the gut microbiome in patients with autism to support healthy functioning.
Butyric Acid Supplementation as an Autism Treatment Option
One of the reasons it is so important for patients with autism to support the health of the gut microbiome is that the bacteria in the gut are responsible for the generation of the bulk of the butyric acid in the colon. Patients can get some of this short chain fatty acid by eating foods that contain animal fats and plant oils, but in general, patients rely on the bacteria in the gut microbiome to produce what they need. Butyric acid plays an important role in the production and function of cells throughout the body, but it is especially important in the colon. By regulating gene expression, mediating signaling protein activity, and serving as an energy substrate, butyrate helps support a healthy GI tract and protect against cellular abnormalities that can trigger debilitating symptoms or even contribute to cancer.
There is also a growing body of research suggesting that butyric acid supplementation can address neurological symptoms in patients with autism. According to a 2017 review paper, symptoms of autism are directly associated with problems with gastrointestinal permeability—commonly called Leaky Gut syndrome. This may be because of defects in intestinal structure like tight junctions. When these protein complexes are not assembled properly, it is easier for metabolites to “leak” out of the brain and into the bloodstream, where they have the potential to disrupt chemical balances in the brain and possibly exacerbate symptoms in patients with autism. Because butyric acid regulates the genes that code for the proteins in tight junctions, patients with ASD who have insufficient butyric acid levels may be more vulnerable to Leaky Gut syndrome, which often comes along with gastrointestinal symptoms like chronic diarrhea, in addition to possible neurological effects.
Considering Elimination Diets for Patients with Autism
In addition to supplementation, there are also several elimination diets that are increasingly popular for patients with autism, the most well-known of which is the gluten-free, casein-free diet. While there are a variety of hypotheses as to why this diet might work, one of the most popular is that eliminating these two proteins from the diet can combat systemic inflammation. Scientists acknowledge that this diet has been widely acclaimed by parents who say that it can “cure” autism, but empirical evidence has yet to offer definitive evidence to support the efficacy of this diet as an autism treatment. Some individual trials have highlighted positive results—such as improved scores for the social interaction and communication subdomains on autism symptom measurement scales—the bulk of the evidence is still mixed. Similarly, specific carbohydrate diets—in which certain types of carbohydrates are eliminated—have been proposed as an autism treatment options, but larger research trials are required to assess their effectiveness. So far, there have been only small studies with mixed results on the GI functioning of patients with autism.
The mixed outcomes of elimination diets for patients with autism may be caused by the complexity of the neurological disorder itself. Autism manifests differently in different patients, and the underlying contributors vary as well. In some patients, the microbial content of the gut may not be sufficient to support the processing of gluten and/or casein, so an elimination diet can make a big difference for both the behavioral and the GI-related symptoms of autism. In other patients, an elimination diet may be less effective.
Choosing the Right Treatment
As our understanding of the relationship between autism, the gut microbiome, and diet grows, it is likely that diet-based treatment options will be further refined, opening up new possibilities for durable symptom remission. However, even today there are promising options for meaningful intervention, including specialized therapies targeting gut microbiome health for the purpose of alleviating autism symptoms. In order to take full advantage of these therapies, it is critical for clinicians to work closely with patients and their families to find well-tolerated treatment options that address each individual’s symptomatology.
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