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Autism spectrum disorder (ASD) is a common developmental disability that affects the way a person communicates and relates to people around them.

The most commonly requested dietary intervention in ASD is a gluten-free and casein free diet.

Theories for a gluten-free and casein-free diet

Treatment with a gluten-free and casein-free diet is based on two theories:

  1. The opiod excess theory of autism. Excess levels of peptides from casein and gluten are thought to be a contributing factor in the typical behaviour seen in children with ASD. Abnormal peptides are found in the urine which suggests that foods are not being broken down completely. It is thought that these peptides may be biologically active and that a small amount crosses into the brain and interferes with neurotransmission causing altered or disrupted activity and sensory input1.
  2. A second theory is based on altered enzyme activity due to problems with the liver. This can lead to gastrointestinal malabsorption because the gut is thought to be more porous which can then have an impact on the central nervous system1.

These theories have lead to the idea that removing gluten and casein from the diet should reduce the symptoms associated with ASD and have a positive impact on communication, attention and hyperactivity.

The majority of research in this area is anecdotal and studies have been done on a very small scale2. There is very little evidence to support using such a restrictive diet in the treatment of people with ASD.

Impact on food choice and nutrition

One area that needs careful consideration before implementing a gluten-free casein free diet is the impact it will have on food choice and nutrition. Children with ASD often have selective eating and therefore already restricted diets. One small research project found that nearly 90% of children with ASD followed repetitive patterns of food choice3

Research has looked at the nutritional intake of children with ASD and considered how this is affected by restrictive diets such as a gluten-free casein free diet 3,4. One study did not find any statistical difference between the dietary intakes of children on exclusion diets and those on a normal diet. 

Another study found that children with ASD had more essential amino acid deficiencies (consistent with poor protein nutrition) than a group of control children. The children on restricted diets had an increased level of deficiency compared to children with ASD on a normal diet. Both these studies were very small scale, and the differences in the findings suggests that larger scale studies are needed4.

For many children with ASD the only foods they will eat are gluten/casein containing foods such as bread and milk. This must be taken into consideration before such a restrictive diet is started.

There is currently not enough evidence to recommend the use of a gluten-free and casein free diet as a treatment for ASD. However, as there is a great deal of anecdotal evidence to support the use of the gluten-free casein-free diet for ASD, it may help certain individuals. The use of this diet needs to be considered on an individual basis.

Good practice guidelines from the British Dietetic Association1 suggest:

  • informing the parent about the lack of evidence and potential harm and benefits
  • considering the current dietary intake of the individual with ASD and the impact of a restricted diet
  • supporting the individual if they still wish to try the diet. A dietitian should advise on and check the nutritional adequacy of the diet
  • a multidisciplinary team approach is strongly recommended
  • ideally the introduction of a gluten-free casein free diet should follow an initial baseline period whereby the individual with ASD follows their usual diet while behaviour and bowel habit is assessed. Gluten and casein containing foods can then be excluded for a specific period of time followed by a period of time when gluten and casein containing foods are reintroduced.

Once it has been agreed that the individual wishes to stay on the diet a follow up plan should be agreed.


1 Isherwood E, Thomas K, Spicer B. (2011). Professional Consensus Statement. Dietary Management of Autism Spectrum Disorder. Dietitians working in Autism supported by the British Dietetic Association Specialist Paediatric Mental Health Groups

2 Knivsberg AM, Reichelt KL, Hoien T, Nodland M.  (2002). A randomised, controlled study of dietary intervention in autistic syndromes. Nutritional Neuroscience 5(4):251-61

3 Cornish E. (2002). Gluten and casein free diets in autism: a study of the effects on food choice and nutrition. Journal of Human Nutrition & Dietetics 15(4):261-9

4 Arnold GL, Hyman SL, Mooney RA, Kirby RS. (2003). Plasma amino acids profiles in children with autism: potential risk of nutritional deficiencies. Journal of Autism & Developmental Disorders 33(4):449-54

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