Furthermore, adhering to the dietary patterns may put people at risk of decreased bone health, reported a team of US scientists in Research in Autism Spectrum Disorders.
Gluten-free foods have rapidly increased in popularity over the past few years – partly as a result of better diagnosis of celiac disease, an autoimmune disorder triggered by exposure to gluten, the protein in wheat, barley, rye and spelt. However, there has also been a mass movement toward gluten-free products by those who have self-diagnosed wheat or gluten intolerance or who believe gluten-free to be a healthier way of eating.
Since it was valued at a modest $580m in 2004, the global market has grown at an average annual rate of 29 per cent and last year was worth $1.56bn, according to Packaged Facts. It could be worth as much as $2.6bn by 2012.
There have also been reports that gluten-free diets for conditions such as autism and multiple sclerosis. The link to autism and its related disorders centers on a hypothesis called the Opioid-Excess Theory whereby people with autism have reduced enzymatic activity, and an increased gastrointestinal permeability. On consumption of proteins like casein from dairy and gluten from cereals this results in toxic by-products of incomplete digestion. These proteins then enter the blood system, cross the blood-brain barrier and interfere with opioid neuro-receptors.
Avoiding such proteins, says the theory, would produce improvements in brain function, therefore. However, the new systematic review challenges such statements.
Researchers led by Austin Mulloy from the University of Texas surveyed the data and identified 15 articles. The overall evidence in support of the Opioid-Excess Theory is “limited and weak”, write the researchers.
So if the theory is weak, what could explain a link between diet and behavior? Mulloy and his co-workers note that food allergy may be behind the effects. “Should a child with ASD experience acute behavioral changes, seemingly associated with changes in diet, practitioners should consider testing the child for allergies and food intolerences, and subsequently eliminate identified allergens and irritants from their environment,” they wrote.
“Should future research support the therapeutic use of gluten-free/casein-free diets, over and above benefits derived from allergen and irritant avoidance, it would seem reasonable to undertake a controlled trial to determine if a gluten-free/casein-free diet had any additional therapeutic benefit for individual children with autism spectrum disorders,” they concluded.
The other researchers were affiliated with the University of California, Santa Barbara (US), Victoria University of Wellington (New Zealand), the University of Italy in Bari, and Texas A&M University.
Source: Research in Autism Spectrum Disorders
Volume 4, Issue 3, Pages 328-339
“Gluten-free and casein-free diets in the treatment of autism spectrum disorders: A systematic review”
Authors: A. Mulloy, R. Lang, M. O’Reilly, J. Sigafoos, G. Lancioni, M. Rispoli