Autism Spectrum Disorder (ASD) is a multifaceted neurodevelopmental condition characterized by persistent deficits in social communication and interaction, alongside restricted and repetitive behaviors and interests. Defined by the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), ASD affects approximately 1 in 100 children globally, with regional variations. Recent data from the United States indicates a prevalence of about 1 in 31 (3.2%) children aged 8 years identified with ASD, while estimates in Asia range from 0.5% to 1% depending on the country. In the United Arab Emirates, the autism rate is reported as 112 cases per 10,000 individuals, highlighting the variability in prevalence across different regions.
The etiopathogenesis of ASD involves a complex interplay of genetic, epigenetic, and environmental factors. Emerging evidence implicates the gut-brain axis-a bidirectional communication pathway linking the gastrointestinal tract and central nervous system-in the development and manifestation of ASD. Children with ASD often present with gut dysbiosis, characterized by reduced microbial diversity and overrepresentation of potentially pathogenic bacteria, which may contribute to altered neurotransmitter regulation and immune function.
A growing body of evidence suggests a connection between diet and ASD symptomatology, particularly for children who experience gastrointestinal issues, which may exacerbate behavioral symptoms. Dietary interventions have gained popularity as potential complementary therapies, based on the hypothesis that gut health may directly influence neurological function and behavior. This connection is primarily understood through the gut-brain axis, a bidirectional communication system linking the gut microbiota with the central nervous system. Children with ASD frequently exhibit altered gut microbiota, leading to speculation that gut dysbiosis could contribute to the severity of ASD symptoms.
This article explores emerging research on nutritional approaches and supports for autistic people, dietary changes, and supplementation. It will concentrate on key areas such as social communication and interaction, repetitive behaviors, restricted interests, sensory issues, cognitive function, and attention.
Sensory Processing and Nutrition in Autism
Autistic children often exhibit higher sensory sensitivity to food compared to their non-autistic peers. This heightened sensitivity can influence their eating habits and dietary preferences. A sensory study on Body Mass Index (BMI) revealed that almost 60% of participants met the criteria for being overweight, while 12% met the criteria for thinness or failure to thrive. These findings, along with other studies, indicate that autistic children have distinct eating and feeding styles compared to their neurotypical counterparts.
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Kelly Barnhill summarizes a study that found that 43 autistic participants had significantly higher histamine and lower thiamine than non-austic controls. These findings suggest the need for further research into potential interventions and screenings that target these biomarkers. A study on the impact of dietary quality on executive function found a correlation between poor dietary quality (high intake of processed carbohydrates) and impaired working memory, executive function, and organizational skills. Study data also showed lower levels of calcium and vitamin D in the autistic group compared to non-autistic controls. Barnhill cites a study that revealed family units of individuals with food sensitivities also present with different eating profiles.
Graf-Myles et al. examined dietary patterns in autistic children, particularly focusing on those adhering to gluten-free, casein-free (GFCF) diets and their possible effects on sensory sensitivities. Notably, sensory sensitivities, particularly those related to taste and smell, influenced food selectivity among autistic children, regardless of diet type. Findings indicated that children on GFCF diets often had reduced dairy intake, which sometimes led to calcium deficiency.
Dietary Changes and Vitamin Supplementation
A growing body of evidence supports the use of dietary changes and vitamin supplementation in managing autism symptoms. A study involving 400 males and 130 females across multiple facilities in the UK tracked nutrition and development over time. The results indicated that adopting a ketogenic diet, with professional support, can be a feasible and appropriate intervention for autistic children. A survey study revealed no significant differences in routine while starting a ketogenic diet, and that it is easy to assist children in starting the diet if necessary.
Barnhill presents a review that found low choline and B vitamins and abnormal amino acids in autistic children compared to non-autistic groups. Another review on probiotic supplementation found evidence that dietary change can increase oxidative stress. The presenter suggests monitoring oxidative stress as a mark of microbiome changes in the future. Clinical literature reviews assert that autistic individuals are often deficient in vitamins A, C, B6, and B12. Across reviews of gluten-free/casein-free (GF/CF) diets, there is consensus that GF/CF diets are quite feasible and carry few adverse effects.
The Ketogenic Diet and Autism
The ketogenic diet (KD), traditionally used for epilepsy management, has gained interest for its potential neuroprotective effects and influence on the gut-brain axis in children with ASD. The KD is a high-fat, very low-carbohydrate diet that forces the body to burn fats rather than carbohydrates.
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Two animal model studies examined the effect of ketogenic diets on mouse behavior. The first study found that mice on ketogenic diets had reduced social and cognitive deficits and repetitive behaviors and an increased abundance of beneficial microbes in the gut, with no adverse side effects reported. A second study found similar results and also indicated that ketogenic diets may restore histone balances in affected mice.
Interventional studies in children with ASD demonstrate that ketogenic diets can shift the gut microbiome, increasing beneficial taxa such as Akkermansia and Blautia, and are associated with increased butyrate kinase expression, reduced pro-inflammatory cytokines, and improved behavioral symptoms. These findings suggest that the ketogenic diet may ameliorate ASD symptoms partly via anti-inflammatory effects and remodeling of the gut-brain axis, although the evidence base is still limited by small sample sizes and short follow-up durations.
Gluten-Free, Casein-Free (GFCF) Diet
The GFCF diet removes all sources of gluten (a protein found in wheat, barley, and rye) and casein (a protein in dairy products). The GFCF diet is based on the hypothesis that individuals with ASD may have sensitivities or intolerances to these proteins, potentially causing gastrointestinal issues and behavioral symptoms. [10].
The GFCF diet has shown promise in addressing social communication and interaction issues associated with autism. Benefits have been observed in metrics related to the Autistic Disorder Index, including improvements in communication, social interaction, and repetitive behaviors, as measured by the Gilliam Autism Rating Scale (GARS-2) (p < 0.0001) [33]. Results showed significant improvement in CARS scores in GFCF group at both follow up points, suggesting potential symptomatic benefits. A study that conducted sensory evaluations of GFCF food products, supplemented over a six-month period for autistic children aged 6 to 12 years, revealed enhancements in behavior patterns, speech, language, communication, and cognitive components following the diet [10]. Individuals undergoing GFCF dietary interventions exhibited significant improvements across various aspects of development and autistic behavior [30]. The results demonstrate significant improvements in non-verbal IQ (p = 0.009), autism symptoms severity as measured by CARS-2 and developmental functioning. However, these positive findings are not consistent across the literature.
Despite mixed findings, some studies support therapeutic diets like GFCF as beneficial. A national survey in the United States showed significant differences in repetitive behaviors, communication, and social interaction before and after a GFCF intervention [28]. Behavioral improvements in some participants on the GFCF diet were suggested to stem from biochemical and neurological origins rather than psychological or educational settings, potentially contributing to increases in verbal and non-verbal communication ( p < 0.05) [43].
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A double-blind, placebo-controlled randomized control trial over 12 weeks with a follow-up involving 31 autistic children, aged 3-5 years, who followed the GFCF diet for 4-6 weeks, some children experienced increased hyperactivity and aggression, as well as transient insomnia lasting 1-3 days, indicating that not all children respond favorably and that close monitoring is warranted [20].
In terms of repetitive behaviors and restricted interests, a review on dietary interventions for ASD assessed the impact of GFCF diets on repetitive behaviors and restricted interests in ASD. The evidence showed limited support for GFCF diets in alleviating these specific symptoms. Although some studies noted improvements in communication and behavior, results were generally inconsistent, and the review concluded that current data do not strongly support GFCF diets as an effective intervention for managing repetitive behaviors or restricted interests in ASD [40]. A randomized clinical trial conducted with 80 autistic children to assess the impact of a GFD on repetitive behaviors. Results showed a significant reduction in repetitive behaviors and improved social interaction in the GFD group (p < 0.05), while no changes were observed in the control group, suggesting potential benefits of GFD for some behaviors in ASD, though further research is needed [16]. Conversely, González-Domenech et al. [17] performed a 12-month crossover clinical trial with 37 ASD participants to evaluate the effects of a GFCF diet. This study found no significant improvements in repetitive behaviors or other behavioral symptoms, following GFCF diet and calling for additional long-term research with stricter controls.
Systematically reviewed the effects of a GFCF diet in individuals with ASD, but neither found robust evidence directly linking the GFCF dietary intervention to specific or consistent changes in gut microbiota composition in this population. González-Domenech et al. further emphasized that, while dietary interventions such as GFCF diets are frequently used in ASD, there is insufficient scientific evidence to support a general recommendation for these diets based on gut microbiota outcomes, and prospective studies with direct microbiota analysis are lacking.
Gut Microbiota and Diet in Autism
Emerging research highlights a significant association between gut microbiota composition and the manifestation of ASD symptoms. Individuals with ASD commonly exhibit gut dysbiosis, characterized by increased levels of Firmicutes and Pseudomonadota and decreased levels of Bacteroidetes, Bifidobacterium, and Lactobacillus [21, 25]. This imbalance in the gut microbiome has been implicated in disruptions to the gut-brain axis-a bidirectional communication system involving the central and enteric nervous systems-which can affect neurological function and contribute to the behavioral and gastrointestinal symptoms associated with ASD [21, 42]. Dysbiosis can lead to increased intestinal permeability ("leaky gut"), allowing pro-inflammatory cytokines and microbial metabolites to enter systemic circulation and cross the blood-brain barrier, thereby influencing neurotransmitter regulation (e.g., serotonin, GABA) and immune responses [42]. These mechanisms may exacerbate core ASD symptoms such as impaired social communication, repetitive behaviors, and sensory abnormalities. Additionally, gastrointestinal symptoms such as constipation, diarrhea, and abdominal pain are frequently reported in ASD and have been linked to specific microbial signatures, including elevated levels of Clostridium and reduced populations of beneficial microbes like Ruminococcus and Gemmiger [25].
Therapeutic strategies targeting the microbiota, including probiotic supplementation (e.g., Lactobacillus, Bifidobacterium), microbiota transfer therapy (MTT), and dietary modifications, have demonstrated promising results in alleviating both gastrointestinal and behavioral symptoms [21, 25]. Moreover, a bidirectional Mendelian randomization study provided evidence of a potential causal relationship between certain gut bacteria and ASD risk, identifying Prevotellaceae as positively associated with ASD and Ruminococcaceae UCG005 as potentially protective [26]. Despite these promising insights, further large-scale and standardized studies are necessary to better understand causal pathways and optimize microbiota-targeted interventions for ASD [25, 50].
Ongoing and Future Research
Barnhill highlights a review of dietary interventions by Amadi et al. She also highlights significant studies from the last year that looked at nutrients/probiotics as anti-inflammatories/modulators (19:00), prenatal diets as a modifier for environmental risk factors for autistic traits (19:50), and assessment and data collection methods across studies (20:35). The speaker outlines an ongoing study in Florida that explores the impact of eating program interventions (22:25). She also highlights an ongoing longitudinal study assessing the effect of therapeutic GF/CF diet and physiotherapy on the gross motor and cognition of autistic children (23:18). Enrollment is currently open for another exciting study that looks at using folic acid to promote language development (24:01). Finally, the first large study on the impact of mitochondrial function and nutrient intervention is also currently being conducted (25:31).
Barnhill considers future avenues of research and underscores that the most significant barrier to nutritional research is a lack of funding. Contemporary research, she continues, should focus on targeted dietary intakes and anti-inflammatory factors.
Additional Considerations
During the Q&A (29:03), Barnhill discusses picky eating and nutrition in adulthood (31:40), feeding therapy and dietary changes (36:00), paleo diets and multivitamins (38:00), and Celiac and autoimmune diseases in autism (44:50). She also considers good sources for protein (51:45), vitamins (55:15), and multivitamins (57:05).