Questions: Do children with autism who are on either an unrestricted diet or the gluten-free casein-free diet have amino acid deficiencies? Are the amino acid deficiencies specific to autism?

Background: The parents and teachers of some children on gluten-free, casein-free diet report that after the initiation of the diet the children are better able to make eye contact and pay attention. As is the case with any diet that does not contain a full complement of nutrients, there have been concerns that the gluten-free, casein-free diet could lead to malnutrition. This study looked at the rates of amino acid deficiencies in children with autism on an unrestricted diet, children on the gluten-free, casein-free diet, and a control group of children with developmental delay but no autistic symptoms.

Amino acids are the "building blocks" of proteins and other substances in living beings. Of the 20 amino acids necessary for proper growth and health in humans (essential amino acids), 9 of them -- histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine -- must be derived from the foods we eat. Deficiencies of any of these amino acids can have negative consequences for health. Among the essential amino acids are those involved in the production of neurotransmitters (chemical messengers found in the brain). For example, tryptophan is converted into serotonin, a neurotransmitter thought to be involved in autistic symptoms. Serotonin excess has been found in some people with autism and bench research continues to look at the role of serotonin in the production of the core symptoms of autism. To date, the increased level of serotonin has been found only in the blood, but not in the brain.

Design: A chart audit was conducted.

Participants: The charts of 150 children with autism who had been evaluated at either of two clinics in Rochester, N.Y., between 1996 and 1998, were examined for any record of blood tests for amino acid levels. The amino acid testing results of 36 children carried out during the course of their original diagnostic work up was used in this study. Of these 36 children, 26 had been eating a regular diet and 10 had been receiving a casein-free, gluten-free diet administered by their parents. The authors assembled a group of children with developmental delay but without autistic symptoms to act as controls.

Method: The blood test results of children with autism who were on the gluten-free, casein-free diet were compared to those of children with autism who received an unrestricted diet. The blood test results of children with autism who were on a regular diet were compared to age- and sex-matched controls who had developmental delay but no autism to see if there were patterns of amino acid deficiency that were specific to autism.

Main Outcome Measures: The blood levels of the amino acids valine, isoleucine, leucine, tyrosine and phenylalanine were measured and recorded as a ratio of tryptophan.

Main Results: There was no profile of amino acid deficiency that was specific to autism. One child with autism was found to have an inborn error of metabolism , leading to an increased level of histidine. Only 1 of 24 children in the control group had an essential amino acid deficiency. In the children with autism who consumed a regular diet, 58% had at least one essential amino acid deficiency and this group were most likely to be deficient in valine, leucine, phenylalanine or lysine. 60% of children with autism on a restricted diet had at least one amino acid deficiency and this group was most likely to be deficient in valine, isoleucine, leucine, phenylalanine, or lysine compared to control children. The children in the restricted diet group were also slightly more likely to be deficient in tryptophan, the amino acid that is a necessary element in the production of serotonin. Isoleucine, leucine and tyrosine were reported as being the most frequently observed deficiencies.

Conclusions: Although there has been no good quality research on the gluten-free, casein-free diet, many parents and educators report that there are marked behavioural improvements in children with autism who are fed this restricted diet. One of the problems is that children on it, or any other restricted diet, can develop protein malnutrition. This study demonstrated little difference between the rates of amino acid deficiency between the children with autism although there were differences in which amino acids were deficient. Both groups of children with autism had some degree of amino acid deficiency, although the children on the restricted diet showed a trend toward greater likelihood of tryptophan deficiency. Only 1 of 24 children with developmental delay but without autism had an amino acid deficiency. Amino acid deficiencies were seen more often in the children with autism vs controls. The deficiencies are likely due to poor nutrition in general due to food selectivity, with deficiencies more likely to be worse in children on a restricted diet.

The study's authors noted that all the children with autism had at least one amino acid deficiency, with only one having a genetic basis for the condition. There was no type of amino acid deficiency that was specific to the children with autism. It was clear that both groups of children had diets that were inadequate to provide the best levels of protein nutrition. The authors speculate that the reason that the gluten-free, casein-free diet appears to reduce autistic symptoms is because it causes a reduction in the abnormal levels of serotonin seen in some children with autism. This is an alternate explanation to the "leaky gut" or opioid peptides theory . The authors emphasize that this was a pilot project that requires duplication with a much larger number of children. The theory they present needs to be confirmed by further research.

It is important to be aware that medical supervision of restricted diets is necessary because of the risk of protein malnutrition.