The medical understanding of autism has changed since it was first described by Kanner.  Kanner believed that autism has a neurological cause, and most researcher and clinician’s did not look for medical explanations to autism, as they believed it was a disorder that was medically untreatable.

Bernard Rimland, a psychologist and father of an autistic son, was the first authoritative voice to dispute the Kanner model.  Rimland established the Autistic Research Institute (ARI) in 1967, and soon scientists and researchers began to come out with new findings and new ideas focusing on medical aspects of autism.

Nowadays science identifies many biological disorders associated with autism, which might contribute to the cause, or aggravate the condition.  The most prominent medical problems identified in many autistic children are gastrointestinal problems, including gastro-esophageal reflux disorder (GERD), pancreatic insufficiency, maldigestion, malabsorption, food intolerance, food allergy, disturbed gut bacteria (dysbiosis), celiac disease, irritable bowel syndrome and inflammatory bowel disease.  These gastrointestinal problems lead to malnutrition and vitamin, mineral and essential fatty acid deficiencies.  Immune dysfunction and chronic inflammation also play a significant role in aggravating the condition.  Numerous metabolic disorders have been identified, including disordered metabolism of neurotransmitters and disorders of metal ion transportation.  It is becoming generally agreed that autism is multifactorial and may be contributed to by many medical issues.

Paul Shattock and Paul Whitely proposed that autism may be a metabolic disorder, whereby biologically derived peptides form dietary gluten and/or casein are not metabolized correctly in autism.  The theory led to widespread use of the Gluten Free Casein Free (GFCF) diet as a biomedical intervention to treat autism.  This diet is highly rated as one of the most effective interventions among parents of autistic children, according to the ARI.  There is continuing research into understanding the mechanisms involved in this diet and some research indicates increased immune response to dietary peptides in autistic subjects.

While research by Andrew Wakefield remains controversial, his work did draw a lot of public attention to gut problems as an underlying cause of autistic behaviours, resulting in new studies by different research groups. For example Horvath found that 69% of non-verbal autistics studied had GERD, and 41% had chronic gastritis and 66% chronic duodenitis.  Disturbed gut bacteria (dysbiosis) seem to play an important role in autoimmune responses, by increased immune response to dysbiotic bacteria and yeast metabolites. In addition many autistics have problems of chronic constipation, which is some cases may be caused by paralysis of the peristaltic movement by bacterial toxins generated by dysbiotic bacteria.  As a result antibacterial and non-absorbed antifungal medications have been used to relieve both gastro-intestinal symptoms and help cognitive function.  

Since the Hanna Poling case there has been increasing interest in possible mitochondrial dysfunction in autistic patients.  Diagnosis of mitochondrial disorders are complex but could be evaluated through serum lactic acid or ammonia, or through nutritional biomarkers for carnitine and coenzyme Q10.  Elevated ammonia can present transiently and chronically in some autistic subjects, and may explain some behaviours and cognitive changes, and neurotransmitter dysregulation in autism.  Control of constipation and dysbiosis is well proven as a treatment for increased ammonia production in the gut.

Autistic symptoms may improve if patients are provided with individualized treatments for poorly recognized problems.   Many of the problems described above can be helped through dietary changes, resulting in improved gut health and nutrient availability.  The GFCF diet, the SCD and GAPS diet, the low sugar low yeast diet, the low allergen diet and the low oxalate diet, can all help the gastrointestinal tract to recovery.  As the gut heals the immune function becomes more regulated, some inflammation is reduced and mitochondria and the metabolism receive better essential nutrition.  This is why diet is particularly important in autism.