Autism is a lifelong developmental disorder affecting as many as 1 in 50 children in the USA (Center for Disease Control 2013), 1 in 100 in the UK and as low as 1.1 in every 10,000 in China. Typically children with autism have difficulty with language, communication, and socialisation. They have problems in learning and display a variety of atypical behaviours. The disorder is accompanied by mental retardation in three out of four cases. Asperger’s syndrome (autism without retardation) is included in the range of different presentations of autism. (1)
The number of cases of autism has noticeably risen in recent years. It is unclear whether this is a result of an increasing awareness of autism spectrum disorders, a change in the way that autism is diagnosed so that cases that were not previously recognized as autism are now included under the diagnosis, or a real rise in the number of cases.
It is likely that there are different causes and different precipitating factors associated with the way that autism is experienced by different individuals. The term “autistic syndrome” is often used to describe a pattern of similar behaviors produced by a variety of triggers. (4)
Several studies have demonstrated abnormal digestive tract function in autistic children. A leaky gut (increased permeability of the membrane lining the digestive tract, which allows food molecules that would normally be excluded to pass into circulation) was demonstrated in some studies (leaky gut is discussed in more detail here). Others found evidence of low activity of intestinal carbohydrate digestive enzymes. (6) The results of these different studies taken together suggest that significant digestive tract pathophysiology may accompany autism, at least within a subpopulation of patients. (4)
However, other studies have refuted these claims. The authors of a UK study published in 2002 concluded that there was not a substantial association between gastrointestinal illness in children and the development of autism. (7) Nevertheless, the authors acknowledged that some children may have had subclinical GI symptoms that were overlooked and that severe GI disease may be associated with autism in certain individuals.
Two separate studies involving a large number of autistic patients reported that an improvement of social, cognitive, and communication skills occurred when they were placed on a diet free of gluten and cow’s milk or a diet free of cow’s milk alone. (8,9)
A 2010 study of 72 children (ages 4 years to 10 years, 11 months) diagnosed with autism spectrum disorder (ASD) indicated that a gluten- and casein-free diet improved the test parameters of the treatment group compared with the placebo control group. (10)
These products are called exorphins to reflect their dietary origin. Gliadomorphins are a family of exorphins released from the partial digestion of the wheat protein gliadin. Similarly, casomorphins are a family of exorphins released upon partial digestion of the milk protein casein. Casomorphins and gliadomorphins have been shown to affect the brain in experimental animals and may be psychosis-inducing agents. (4)
The Hyperpermeable Digestive tract (Leaky Gut) in Autism
In some autistic children the opioid peptides from the diet move through the lining of the digestive tract into blood and are carried to the brain as the blood circulates through the various organs in the body. This was found when it was discovered that the epithelium lining the digestive tract in some autistic children was more permeable than normal. (11) Thus, the “leaky gut hypothesis” was proposed (see here for more on the leaky gut). (4,12,13)
It was suggested that because of the increased permeability, larger molecules than normal are able to pass through the lining of the digestive tract into circulation. Digestion products of natural foods such as casein and gluten-containing grains may thus be able to elicit immunological responses and interfere directly with the central nervous system.
A 2010 study (13) demonstrated that a significantly greater percentage of patients with autism and their close relatives had considerably higher scores on the intestinal permeability test (IPT)—36.7% and 21.2%, respectively—than the nonautistic population (4.8%). (Details of the lactulose/mannitol permeability test used in determining intestinal permeability are provided beloa.) The authors suggest that the increased IPT levels found in first-degree relatives indicates the possibility of an intestinal (tight-junction linked) hereditary factor in the families of subjects with autism. The study further reported a significant decrease in the IPT scores in autistic persons following a gluten- and casein-free diet.
There is a lack of evidence to suggest that casein, gluten, or their products cause the leaky gut. However, some researchers equate the process to celiac disease (14) in which immunological reactions to the gliadin fraction of gluten damage the intestinal villi that line the digestive tract epithelium and may result in hyperpermeability. Other studies (15) suggest that the improvement of autistic children on a gluten-free diet indicates that malabsorption of essential nutrients in celiac disease predisposes to symptoms of autism.
Vitamin B-12 Deficiency and Nervous System Development
A deficiency in an essential nutrient has often been suggested as a possible contributor to some types of autism. Vitamin B-12 was thought to be a likely candidate because undetected and untreated vitamin B-12 deficiency in infants can result in permanent neurological damage. Furthermore, individuals with stomach and small intestine disorders may be unable to absorb enough vitamin B-12 from food to maintain healthy body stores.
According to the proponents of the theory that vitamin B-12 deficiency may play a role in certain types of autism, pathology in the lining of the ileal region of the small intestine in autistic children, which has been observed in a few studies, could interfere with vitamin B-12 being transported into circulation. (16)
If absorption is severely inhibited, the resulting lower blood vitamin B-12 could interfere with the formation of myelin, the lipoprotein material surrounding the axon of certain nerve fibers. Myelin is necessary for normal conduction of the nerve impulse (action potential) in myelinated nerve fibers. Therefore, impairment in nerve conduction could result in the neurological deficits observed in autism. However, direct evidence of vitamin B-12 deficiency and impaired myelin formation in autism is lacking at this time.
A 2010 study (17) of 3- to 8-year-old autistic children indicated that vitamin B-12 supplementation improved autistic symptoms in 9 (30%) of their subjects, suggesting that a subset of children with autism disorder may benefit from B-12 supplementation. In general, authorities suggest regular monitoring of the B-12 levels in the blood of autistic children and supplementation, usually by injection, if the levels are found to be abnormally low. Ensuring that the diet includes adequate levels of vitamin B-12 is an obvious measure for ensuring optimal nutrition in any child, but especially autistic children whose diet may be rather unbalanced because of their own food preferences.
Since 1980, numerous published studies have attempted to assess the effects of vitamin B-6 and magnesium on a variety of characteristics such as verbal communication, nonverbal communication, interpersonal skills, and physiological function in individuals with autism. (18) These studies were subject to scientific evaluation and review (19) in 2003. The authors concluded that due to insufficient evidence, they could provide no recommendations on the use of vitamin B-6 with magnesium as a treatment for autism.
Some clinicians have been investigating the possibility that magnesium alone as a supplement may improve symptoms in autism. This was based on the observation that children with autistic spectrum disorders had significantly lower plasma concentrations of magnesium than normal subjects. (20) Because magnesium is an essential element in several important physiological processes, it has been suggested that a deficiency might lead to impairment in certain brain functions that could contribute to the autistic disorder. However, studies on magnesium and its role in autism have not yet defined the deficiency or determined whether supplementation with the mineral is effective in treatment.
Currently, experts do not agree on whether dietary manipulation can help prevent autism or aid in its treatment. Researchers in the field tend to agree that dietary manipulation is recommended if the child’s behavior improves on the restrictions or supplements. However, many practitioners hold the opinion that “the link between autism and a gastrointestinal pathophysiology is not substantiated by research. The dietary approaches employed are cumbersome, not proven to be efficacious, and may further narrow the food choices of the child with autism.” (22)
If any dietary manipulation provides some improvement, parents, caregivers, and clinicians are usually open to a trial on the suggested diet. If a parent feels there is a chance that their child might benefit from a gluten- and casein-restricted diet, it may be worthwhile to try the diet—for a limited time only. If the child’s behaviour does not noticeably improve after strictly adhering to the guidelines for a month, then the restrictions should be abandoned because it is unlikely that they are providing any benefit. As with any dietary manipulation, it is essential that any foods removed from the diet be replaced with those of equivalent nutritional value.
No evidence suggests that very high doses of any single nutrient are beneficial. In fact, the contrary is usually true. Excessive quantities of many vitamins and minerals can be toxic, and frequently, excess of one leads to deficiency in another, as they compete for absorption and metabolites. Each nutrient plays an essential role in keeping the body healthy; refer to the Dietary Reference Intakes (DRIs) published by the Institute of Medicine for recommendations about the levels of various nutrients that are ideal at each developmental stage. (23)
The Tolerable Upper Limits set in the DRIs should not be exceeded except in specific medical conditions, which will be decided by a medical specialist in individual cases. Further studies are needed to establish the efficacy of any dietary intervention in the management of autism, to identify those individuals who would most benefit, and to determine the mechanism responsible for triggering any adverse responses.
For client education on a gluten- and casein-free diet and other topics related to food allergies and intolerances, look for Food Allergies and Intolerances: Client Education Tools for Dietary Management in the Academy of Nutrition and Dietetics online store.
First Published in 2014
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