Autism and Autism Spectrum Disorder (ASD) are specific neurological disorders that affect the brain, frequently characterised by challenging paediatric behaviour. The current narrative review using PubMed and Google Scholar was conducted in line with the Preferred Reporting Items for Systematic review and Meta-Analysis Protocols, and comprised randomised controlled trials and clinical control trials with gluten-free, casein-free (GFCF) diets published till 2020. Of the 80 studies selected, 7(8.75%) were included in the review. It was observed that the gluten-free, casein-free diet was safe with therapeutic benefits in autistic children. Therefore, a tailored dietary approach can be a beneficial management regimen. The trials related to utility of gluten-free, casein-free diet among autistic children are sparse, with limited sampling size, and indication of bias in the findings. Therefore, larger cohort studies on gluten-free, casein-free trials are required to provide further insight into the therapeutic benefits of the diet.
Keywords: Autism, Autism spectrum disorder, Gluten-free and casein-free diet, Randomised controlled trial.
Autism is a neurodevelopmental disorder frequently characterised by challenging social behaviour and impaired linguistic skills. It is usually exhibited in the initial three years of life, but a few are diagnosed after the age of five years.1 It is observed that autistic children lack the ability to properly digest proteins, mainly casein and gluten, leading to synthesis of brain-altering harmful compounds, like opioid peptides, and their elevated systematic levels lead to manifestation of perplexing behaviour.2 Casein, a phosphor-protein, is obtained from animal sources, like milk and dairy products, while gluten is derived from plant sources belonging to the grass family of wheat, oats and rye.3 Both the proteins share a similar molecular structure and, as explained earlier, their incomplete digestion may result in the production of exorphins or exogenous opioid peptides. Exorphins generating from gluten and casein include gluteomorphins/ghadorphin and casomorphins, respectively, which are permeable to gut lumen and blood-brain barrier exerting central opioid-like actions, leading to bewildered and disconcerted behaviour.4 Therefore, a diet exclusive of casein and gluten may facilitate the elimination of opioid peptides from the body, assisting in the diminution of autistic symptoms.5
Research conducted in Arizona in 2005 showed that children and adults with autism/autism spectrum disorders (ASDs) often exhibit nutritional deficiencies, metabolic imbalances, gustatory concerns and abdominal impediments, directly influencing physical growth, neurological development and sustenance. Several nutritional and dietary interventional trials have shown mitigation of these debilitating underlying disorders through scrupulously tailored dietary approach.6
A study conducted in New York in 2015 suggested that therapeutic dietary interventions are provided to use by approximately 15-38% of autistic children worldwide. The most prevalent dietary intervention known is the gluten-free/casein-free (GFCF) diet which comprises food devoid of gluten and casein.7 With the findings of another interesting fact in autistic children of having leaky gut, which allows permeability of undigested food, microorganisms and contaminants to portal circulation further strengthens the established concept of absorption of partially digested protein by-products, especially opiates in blood, leading to behavioural deficits in such children.6 As gluten and casein proteins cannot be properly digested in the gut of the affected children, the emergence of GFCF diet came to prominence to facilitate the mitigation of stunted physical and mental growth of children with autism and ASDs.9,10
Materials and Methods
The narrative review included interventions on the utility of GFCF diet for the management of autism/ASDs through randomised controlled trials (RCTs) and clinical controlled trials (CCTs) published in any language between 1999 and 2020. The review was carried out in accordance with the updated guidelines for Preferred Reporting Items for Systematic review and Meta-Analysis Protocols (PRISMA-P).11 The search engines included PubMed and Google Scholar, and the literature search was done using the terms: "Autism" Or "Autism Spectrum Disorder" Or "Paediatric Autism and "Diet" And "Casein Free" Or/And "Gluten Free" And "Randomised Control Trial".
The databases were scanned separately by two senior researchers for studies based on their titles and abstracts, accompanied by a sampling of complete texts. Via discussion between the authors, all disagreements were resolved.
The studies included were those published in any language between 1999 and 2020 evaluating the effectiveness of GFCF diet through RCTs and CCTs in which the dependent variable needed to be correlated with autism/ASD behavioural symptoms. Also, the included articles were original comparative studies, involved a control group, and delivered adequate detail on methods and results.
The studies excluded were studies that were not RCTs or CCTs, and so were books, conference papers, theses, editorials, case notes, case studies, analyses and publications without full text. Reviews, meta-analyses, in vitro studies and studies on non-human subjects were also eliminated.
A data extraction form was used to extract the following information: research design, demographic variables analysed, description of the experiment, its duration, progress measures, measurement methods, and qualitative and quantitative data.
The included studies were finally assessed for suitability under the National Institutes of Health (NIH) RCT scoring criteria 12, and the studies were graded as excellent, good and fair.
The initial classification of quality evidence was established from the research design of RCTs and CCTs. Aspects that could minimise or improve the quality were also investigated from the original classification. Methodological limitations, inconsistencies, unreliable proof, inaccuracy, and publication bias, like factors responsible for decrease in the degree of evidence, were also noted. Treatment-response gradient, wide gradient magnitude and residual confounders were also evaluated from the trials.
The search identified a total of 80 studies; 9(11.25%) on PubMed and 71(88.75%) on Google Scholar. Of the total, 7(8.75%) were selected as potentially relevant (Figure). Of the studies reviewed, 6(85.7%) were graded as excellent and 1(14.3%) as fair (Table-1). The studies used Autism Treatment Evaluation Checklist (ATEC), the Behavioural Summarised Evaluation (BSE), the Aberrant Behaviour Checklist (ABC) scales to check disease severity (Table-2).
A randomised double-blinded trial for the determination of effectiveness of GFCF diet in treating autism[10 included 15 children ranging in age from 2 to 16 years, and established the foundation of the GFCF as beneficial in the diminution of autistic behaviour, and provided prospective research directions for future studies.
Another randomised placebo trial13 found that the treatment group receiving GFCF diet improved significantly compared to the control group. A total of 67 subjects were enrolled, including 50 non-signing neurotypicals of similar age and gender as controls and treatment subjects with ASD aged 3-58 years. It was observed that a combination of dietary supplements with balanced diet were successful in minimising autism symptoms and gastrointestinal disorders, leading to enhanced emotional, behavioural, cognitive and learning abilities.
Another RCT7 was conducted with 14 autistic children aged 3-5 years for the determination of safety and effectiveness of the GFCF diet. It was found that the GFCF diet, when combined with nutritional therapy, improved mental wellbeing in the affected children.
Another RCT9 suggested the utility of the GFCF diet for better developmental outcomes in ASD children.
A single-blind study to assess the effectiveness of GFCF diet for autistic children and the prevalence of urinary peptide abnormalities among them revealed that children who were placed on a GFCF diet performed better than those who were not.14
Another RCT comprised complementary treatments, such as GFCF diets, that are widely used in the absence of effective drugs for ASDs. The researchers wanted to see if the GFCF diet influenced behaviour problems in ASD individuals, and if there was a connection between urinary beta-casomorphin levels and behaviour problems. This crossover analysis included a total of 37 patients. Each patient followed a normal diet, including gluten and casein, for six months before switching to GFCF diet for another six months. The treatment order (normal diet first or GFCF diet first) was chosen at random. The patients were evaluated at three different points in time; at the beginning of the study, after normal diet, and after GFCF diet. Questionnaires on behaviour, autism, and dietary adherence were completed at each time point, as well as urinary beta-casomorphin concentrations were measured. There were no major behavioural changes or correlations with urinary beta-casomorphin concentrations following the GFCF diet. There were no important effects of a 6-month GFCF diet on autism developmental symptoms or urinary beta-casomorphin concentrations.15
Another RCT investigated the impact of dietary intervention using dietary guidebooks on autistic children's behavioural symptoms. Some autistic behavioural deficits were found improved in the GFCF diet community, including improved concentration, improved sleeping habits, and hyperactive and anxious behaviour.5
Healthcare systems continue to confront the accelerating and complex problem of ASDs. Autism's emotional variation varies from person to person, making management challenging and necessitating personalised treatment. The advantages of dietary intervention are greater as symptomatic changes were seen after a properly followed GFCF diet, laying the groundwork for a diet that will undoubtedly benefit the affected children.5
The current narrative review indicates that there is a dearth of data in this area, both in terms of quality and quantity. This is based on several limitations discovered, particularly those related to scarcity and uncertainty of available data, such as methodological limitations linked to a variety of factors, such as the lack of a control group, unclear definitions of inclusion criteria, very small sample sizes and examinations based on single individuals, heterogeneous groups in terms of age, and so on. There was also the possibility that data on behavioural variables could be skewed over time due to memories of parents and other relatives, and that these changes in participant behaviour could be influenced even more by the fact that they were participating in non-blinded study trials.16
Gonzalez-Domenech et al. conducted an RCT involving autistic children, and, after 6 months of dietary intervention, found no substantial amount of beta-casomorphin in the urine of autistic children, indicating that the GFCF diet had no effect on them. Similarly, a placebo effect may have influenced the results. Finally, such predispositions as the likelihood of confounding bias can be related to mental improvements as a result of continuous learning and behavioural therapy, rather than to the GFCF diet.15
Knivsberg et al. conducted a single-blind controlled study having 20 autistic children. After a year, findings and experiments were performed which showed that people in the diet group had substantially less autistic behaviour than those in the control group.17
Previously, a systematic review concluded that there is a lack of evidence supporting the use of the GFCF diet for ASD treatment. It looked at 6 RCTs that were not blinded and a single-blind RCT, and concluded that data was insufficient to draw a valid conclusion since most of the studies lacked a control group.18 Another systematic analysis found that removing the GFCF diet did not result in a substantial increase in ASD symptoms. Moreover, it stated that 3 of the 5 studies concluded that GFCF diet was not beneficial for autistic patients.19 Millward et al. in 2008 found an important effect of GFCF diet on autistic traits, pointing out wider confidence intervals in the study outcomes.20 Another research, published in 2013, was similar to earlier systematic reviews in stressing the possibility that incorrect and insufficient data about the GFCF diet could be linked to genetic variances among people with ASD.21
The current narrative review did not include any study conducted on autistic individuals in Pakistan as there is lack of data at the national level. As such, the findings cannot be generalised to Pakistani population. Large-scale clinical trial or research must be done with adjuvant therapy of non-pharmacological diet in the country.
Huge family data is required to increase the research momentum. Also, there is a need to collect large dietary intervention data to analyse the results.
Acknowledgement: We are grateful to the Department of Biological and Biomedical Sciences for its immense support during the write-up.
Conflict of Interest: None.
Source of Funding: None.
1. Taylor B, Miller E, Lingam R, Andrews N, Simmons A, Stowe J. Measles, mumps, and rubella vaccination and bowel problems or developmental regression in children with autism: population study. BMJ. 2002; 324:393-6.
2. Madsen KM, Hviid A, Vestergaard M, Schendel D, Wohlfahrt J, Thorsen P, et al. A population-based study of measles, mumps, and rubella vaccination and autism. N Engl J Med. 2002; 347:1477-82.
3. Croonenberghs J, Bosmans E, Deboutte D, Kenis G, Maes M. Activation of the inflammatory response system in autism. Neuropsychobiol. 2002; 45:1-6.
4. Halsey NA, Hyman SL. Measles-mumps-rubella vaccine and autistic spectrum disorder: report from the New Challenges in Childhood Immunizations Conference convened in Oak Brook, Illinois, June 12-13, 2000. Pediatrics. 2001; 107:E84.
5. Peerkhan N, Wesely E, Nishadevi V. Impact of Casein and Gluten Free Dietary Intervention on Selected Autistic Children. Iran J Pediatr.2008; 18:244-50.
6. Cekici H, Sanlier N. Current nutritional approaches in managing autism spectrum disorder: A review. Nutr Neurosci. 2019; 22:145-55.
7. Hyman SL, Stewart PA, Foley J, Cain U, Peck R, Morris DD, et al. The Gluten-Free/Casein-Free Diet: A Double-Blind Challenge Trial in Children with Autism. J Autism Develop Disord. 2016; 46:205-20.
8. Whiteley P, Rodgers J, Savery D, Shattock P. A Gluten-Free Diet as an Intervention for Autism and Associated Spectrum Disorders: Preliminary Findings. Autism. 1999; 3:45-65.
9. Whiteley P, Haracopos D, Knivsberg AM, Reichelt KL, Parlar S, Jacobsen J, et al. The ScanBrit randomised, controlled, single-blind study of a gluten- and casein-free dietary intervention for children with autism spectrum disorders. Nutr Neurosci. 2010; 13:87-100.
10. Elder JH, Shankar M, Shuster J, Theriaque D, Burns S, Sherrill L. The gluten-free, casein-free diet in autism: results of a preliminary double blind clinical trial. J Autism Develop Disord. 2006; 36:413-20.
11. Liberati A, Altman DG, Tetzlaff J, Mulrow C, Gøtzsche PC, Ioannidis JPA, et al. The PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate healthcare interventions: explanation and elaboration. BMJ. 2009; 339:b2700.
12. Bilal Ahmed S, Obieta A, Santos T, Ahmad S, Elliot Ibrahim J. Effects of non-pharmacological interventions on disruptive vocalisation in nursing home patients with dementia-A systematic review. Front Rehabilit Sci.2022; 106:12-32.
13. Adams JB, Audhya T, Geis E, Gehn E, Fimbres V, Pollard EL, et al. Comprehensive Nutritional and Dietary Intervention for Autism Spectrum Disorder-A Randomized, Controlled 12-Month Trial. Nutrients. 2018; 10:369.
14. Knivsberg AM, Reichelt KL, Høien T, Nødland M. A randomised, controlled study of dietary intervention in autistic syndromes. Nutr Neurosci. 2002; 5:251-61.
15. González-Domenech PJ, Díaz Atienza F, García Pablos C, Fernández Soto ML, Martínez-Ortega JM, Gutiérrez-Rojas L. Influence of a Combined Gluten-Free and Casein-Free Diet on Behavior Disorders in Children and Adolescents Diagnosed with Autism Spectrum Disorder: A 12-Month Follow-Up Clinical Trial. J Autism Develop Disord. 2020; 50:935-48.
16. Marí-Bauset S, Zazpe I, Mari-Sanchis A, Llopis-González A, Morales-Suárez-Varela M. Evidence of the gluten-free and caseinfree diet in autism spectrum disorders: a systematic review. J Child Neurol. 2014; 29:1718-27.
17. Knivsberg AM, Reichelt KL, Høien T, Nødland M. Effect of a Dietary Intervention on Autistic Behavior. Focus Autism Develop Disabil. 2003;18:248-57.
18. Christison GW, Ivany K. Elimination diets in autism spectrum disorders: any wheat amidst the chaff? J Develop Behav Pediatr. 2006; 27:(supply 2): S162-71
19. Hurwitz S. The Gluten-Free, Casein-Free Diet and Autism. J Early Intervent. 2013; 35:3-19.
20. Millward C, Ferriter M, Calver S, Connell-Jones G. Gluten- and casein-free diets for autistic spectrum disorder. Cochrane Database Syst Rev. 2004; 11:CD003498.
21. Buie T. The relationship of autism and gluten. Clin Ther. 2013; 35:578-83.