Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by impaired social communication and repetitive behavior patterns. While the exact pathology of ASD is unknown, there may be a connection between diet and ASD behavioral symptoms.
Many dietary supplements have been investigated as potential treatments, including omega-3 fatty acids, melatonin, vitamin D, and a combination of vitamin B6 and magnesium; but the gluten-free and casein-free (GFCF) diet has become one of the more popular interventions among parents with ASD children.
Survey have shown that anywhere from 20% to 70% of respondents have tried a GFCF diet. Parents often report symptom improvement when placing their children on this diet, but what do results from randomized controlled trials (RCTs) tell us?
What is the theory behind the GFCF diet?
The opioid-excess theory of ASD has long been a popular hypothesis for explaining how a GFCF diet may alleviate ASD behavioral symptoms. It has three main components:
These peptides can enter the body through an abnormally permeable intestinal border, which is speculated to be more common in people with ASD.
If produced in sufficient quantities, these peptides could theoretically cross the blood–brain barrier and interfere with normal brain development.[8
This hypothesis, however, is being disputed. Some studies did report greater gut permeability in people with ASD, but others saw no difference. Moreover, highly sensitive measurement techniques consistently failed to find detectable concentrations of opioid peptides in the urine samples of patients with ASD. If significant amounts of opioid peptides were making it past the gut and into the bloodstream, urine tests should reveal their high levels as the body worked to eliminate them.