The role of diet in autism spectrum disorders

Published: 18-10-2020

It is not difficult to find information on the internet about the benefits of a special diet in children with autism spectrum disorder (ASD). Most often, parents decide to introduce a gluten-free and dairy-free diet, but it is not a problem to find positive information also about other diets. The problem, however, is finding scientific publications that confirm their effectiveness. Although research into the effectiveness of diets in treating symptoms of autism is being conducted, it is often difficult to draw conclusions.

Gluten-free and casein-free (dairy-free) diet and autism

The recommendation of a gluten-free and dairy-free diet (GFCF diet) is based on the hypothesis of opioid excess. According to this hypothesis, symptoms of autism can be caused by opioid peptides, which are produced by incomplete breakdown of gluten (a protein in some grains) and casein (a protein in milk). Increased intestinal permeability, called leaky gut syndrome, causes these peptides to enter the bloodstream, from where they then cross the blood-brain barrier to the central nervous system and disrupt the endogenous opioid system and neurotransmission.

The gluten-free and casein-free diet is the most researched diet for autism spectrum disorder, but the conclusions are still unclear. Some studies indicate that children with autistic disorders are more likely to suffer from digestive system disorders than children without ASD, which could support the opioid hypothesis, but other studies do not confirm this. Research focusing on leaky gut syndrome is also inconsistent, and one confirms that children with autistic disorder are more likely to have leaky gut syndrome than other children, but other studies contradict this. If the hypothesis about incomplete breakdown of gluten and casein is consistent with reality, people with ASD should also have an increased concentration of opioid peptides in the urine, but here the research results are also inconsistent (cited: Mulloy et al. 2009).

Mulloy and colleagues conducted in 2009 a review of research into the effects of a gluten-free and casein-free diet on symptoms of autism. They found 14 studies in which a total of 188 people participated. 7 of these studies were positive, 4 negative, 2 partially positive and partially negative, and for one study it was not possible to determine whether the results were positive or negative. Researchers also noted that due to methodological flaws, no study can fail to draw certain conclusions, and moreover, studies that gave positive results were methodological weaker than those that gave negative results. The most common shortcoming was the lack of control whether the changes in behavior could be caused by factors other than diet. Other studies have included shortcomings such as no control group, no measurement of inter-observer agreement, or no blinding of the sample (based on observations from parents and teachers who knew the child was on a diet).

The latter increases the risk of the placebo effect, since believing that the diet will help the child may influence the perception of the child’s behavior and its behavior. First, a parent who believes diet helps may begin to notice positive behaviors in their child that were actually present before the diet was introduced. Second, if a parent is more likely to start paying attention to the child’s positive behavior and therefore praise it more often, it may actually cause the change in the child’s behavior to actually take place. This is why blinded studies in which assessments of a child’s behavior are made by those who do not know whether the child is on a diet or not have more methodological value. Even more valuable would be double-blind studies, i.e. those in which the parents not only do not assess the child’s behavior, but also do not know whether the child is on a diet.

Only one double-blind study has been performed so far (Elder et al. 2006). In this study, the food products were provided to parents by nutritionists, and the parents were not informed whether they were gluten-free, casein-free, or plain. The behavior of the children was assessed by two independent observers, based on home videos taken at the start of the study, after 6 weeks and after 12 weeks. According to the results of the study, there were no differences between behavior and urinary peptide levels in children who were on a gluten and dairy free diet and those who were on a regular diet, although some parents said they noticed improvements in their child’s speech and behavior. The big disadvantage of this study, however, is the small group of participants – only 13 children, which could have contributed to the lack of statistical differences between the experimental group and the control group.

Based on their research analysis, Mulloy and colleagues concluded that the diet should only be introduced if the child has a medically confirmed allergy or intolerance to gluten and / or casein.

One of the more recent studies (Pennesi and Cousino-Klein, 2012) supports their recommendations. The disadvantage of this study is that the results are based on the observations of parents that were collected through an online survey, but the advantage is the large number of participants (387). The results showed that the effectiveness of the gluten-free and dairy-free diet (GFCF diet) was greater in children who had digestive problems or diagnosed food allergies than in children who had no gastrointestinal symptoms prior to the introduction of the diet. Not only did the physiological symptoms such as diarrhea and constipation improve, but also the symptoms of autism (e.g. reduced self-stimulating behavior, hyperactivity, echolalia) and social behavior (e.g. increased eye contact, improved speech, attention).

It is also worth noting that parents who followed the diet for 6 months or less indicated that it was less effective than the parents of children who were on the diet for a longer period of time. It is possible that in some children the effect of the diet may not become apparent until after a few months, and too short a study period may sometimes cause negative results. Mulloy and his colleagues also noted in their analysis that studies that did not show a positive effect of diet were conducted shorter (from 4 days to 3 months, on average 5 weeks) than those that showed a positive effect of the diet (from 14 weeks to 4 years, 18 months on average).

One of the larger studies was also conducted by Whiteley et al. (2010). The participants of their study were 72 children, aged 4-10 years, and the study lasted 24 months. Some participants dropped out, however, and after 12 months there were 55 participants. However, after 8 months, an improvement was observed in the group of children who followed a gluten-free and dairy-free (GFCF) diet, and tests carried out after 12 months confirmed the beneficial effect of the diet. There were improvements in social interaction, inattention and hyperactivity decreased, and more points were obtained in the daily life skills test. However, it cannot be ruled out that other factors, such as other therapies that the children received in the meantime, may have an effect on the improvement.

Despite the favorable results, Mari-Bauset et al., who reviewed the 2013 research on the effects of gluten-free and casein-free diets on symptoms of autism, came to the same conclusions as Mulloy et al. four years earlier. They recommend adopting a gluten-free and dairy free diet only in the case of a diagnosed intolerance or allergy to gluten and casein.

Although the studies that have been carried out so far do not confirm that a gluten-free and dairy-free diet is recommended if the autistic child is not allergic or intolerant to gluten and casein, its beneficial effects on such children cannot be excluded. It is possible that such a diet will be effective even if your child does not have allergy symptoms or digestive problems, but you should weigh the pros and cons before deciding to introduce a diet. A special diet can make socialization difficult because it is a socially isolating factor. A child on a gluten-free and dairy-free diet during meetings with their peers cannot eat what they do; they cannot, for example, go to a pizzeria, eat a burger at McDonald’s or other popular products among children. Such a diet can also lead to a deficiency of certain nutrients. Children with autistic disorders often have a limited menu anyway, because many products do not want to eat, and a gluten-free and dairy-free (GFCF) diet further restricts the variety of products. Some studies have shown slower growth and reduced bone thickness and density in children with ASD on a dairy-free diet, while others have shown a high ratio of omega-6 to omega-3 fatty acids and a low level of DHA and EPA polyunsaturated fatty acids (after Mari-Bauset et al. ., 2014 and Mulloy et al. 2009). In addition, many gluten and dairy free products are expensive, and it is worth noting that such a diet has practical difficulties, such as the problem of eating out.

Gluten-free diet and autism

While most of the research into the effects of diet on autism spectrum disorder has focused on gluten-free and casein-free diets, there is some research showing that shedding only gluten from the diet may be beneficial.

The data show that 22% of people with celiac disease develop some kind of neurological or psychiatric disorder (after: Jackson et al. 2012). Celiac disease is a disease in which gluten makes the immune system react against its own tissues. Common symptoms are bloating, fatty diarrhea and weight loss, and gluten consumption in celiac disease leads to villi atrophy. Celiac disease is diagnosed by intestinal biopsy, but blood tests (determination of the level of appropriate antibodies) and genetic tests also play a role in the diagnosis.

Genuis and Bouchard (2010) presented a case study of a 5-year-old boy with severe autism. In addition to developmental delay and major communication problems, the boy also presented, inter alia, frequent unexplained fatigue and confusion, and could not tolerate bright light, and often put his fingers in his ears. He also had difficulty falling asleep, frequent nightmares, depressed mood and easily angered. In addition, he had digestive problems such as bloating, belching, abdominal pain, frequent nausea, vomiting and diarrhea. Antibody tests showed celiac disease, so doctors introduced a gluten-free diet. In addition, the boy was taking vitamins A, D and E, omega-6 and omega-3 fatty acids, and folic acid, as studies showed a deficiency of these ingredients. Within a month of introducing the diet, the problems with the digestive system disappeared and the boy’s behavior improved significantly. Within three months, his condition improved so much that he no longer needed individual tuition and was able to attend a regular class without an assistant.

Based on the history of one person, of course, it cannot be concluded that the introduction of a diet will bring such good results in every person with autism and celiac disease, however, history shows how much celiac disease can affect the nervous system (although it is possible that at least partially the therapeutic effect was achieved by supplementation vitamins and acids).

In 1997, Pavone et al. conducted a study to find out whether celiac disease is more common among people with autism than among people without a diagnosis of autism. Their research has not shown such a link, but in recent years, more and more is known about gluten sensitivity, which is different from celiac disease and gluten allergy. Research shows that gluten sensitivity is 6 times more common than celiac disease and does not cause intestinal villi disappearance and is associated with other antibodies in the blood (cited: Jackson et al. 2012).

A study on the effect of a gluten-free diet on symptoms of autism was conducted by Whiteley and colleagues (1999). A total of 42 children participated in the study. 31 of them switched to a gluten-free diet for 5 months (22 adhered to the diet and only those were included in the analyzes), 5 children who had been on a gluten-free diet from 6 months were switched to the regular diet during the study, and 6 children were the control group. Observations from parents and teachers showed that many of the children who went gluten-free improved. The most common improvement was in communication, concentration and aggressive behavior. However, among parents who introduced gluten to their children’s diet, some noticed worsening of symptoms. Some children showed an increase in impulsivity and hyperactivity, and in others an increase in stereotypical and aggressive behaviors, or a slight deterioration of communication skills.

Due to the lack of a blind sample and the small number of participants in the study, certain conclusions cannot be drawn about the effectiveness of a gluten-free diet in ASD, but there is no doubt that if a child with autism spectrum disorder shows symptoms of the digestive system, such symptoms should not be underestimated and it is worth carrying out appropriate research or visiting a dietitian.

The ketogenic diet and autism

The ketogenic diet, also known as the keto diet, is a high-fat, low-protein, and low-carbohydrate diet. A very high fat intake causes the body to develop a state of ketosis, in which energy is no longer drawn from glucose and it begins to be drawn from the ketone bodies that result from the breakdown of fats. The diet is followed 2-3 years after the initial fasting period, which increases the concentration of ketone bodies (cited: Kawicka and Regulska-Ilow, 2012).

The ketogenic diet began to be used in the 1920s to treat epilepsy. However, in treating seizures in people with Rett syndrome, it has been found that diet sometimes has a positive effect on their behavior as well (Evangeliou et al. 2003). Rett syndrome is characterized in some respects by symptoms similar to autism, and there are preliminary studies showing a beneficial effect of such a diet in people with autistic disorder.

A study by Evangeliou et al. (2003) involved 30 children with autism spectrum disorders. The diet was followed for 6 months, with a two-week break from the regular diet after every 4 weeks of the ketogenic diet. 7 children did not tolerate the ketogenic diet, in 5 the parents gave up the diet after 1-2 months, while the rest showed improvement, at least slightly. The greatest improvement was seen in children who had mild autistic disorders before introducing the diet. Those with a more profound disorder had less improvement.

More recent studies (Ruskin et al. 2013), conducted in mice, also showed a beneficial effect of a ketogenic diet on symptoms of autism.

Hozyasz et al. (2010) also noted that the improvements some parents notice in their children after adopting a gluten-free diet may in some cases be in fact due to ketone bodies. Many parents choose to introduce a gluten-free diet without consulting a dietitian, and an improperly balanced gluten-free diet is often a high-fat diet, which can shift your metabolism into the ketogenic pathway. So far, however, no studies have been conducted that could confirm or disprove this hypothesis.

The research conducted so far on the ketogenic diet in autism spectrum disorders, although optimistic, should be treated as preliminary. More patient studies are needed to determine if this diet is appropriate. It is not recommended to introduce a ketogenic diet in a child on your own, because it is associated with the risk of metabolic disorders. While on a ketogenic diet, blood ketone levels should be checked regularly (Kawicka and Regulska-Ilow, 2012).

Dietary supplements and autism

Kawicka and Regulska-Ilow (2012) conducted a review of research on the effects of vitamins and other nutrients on symptoms of autism. There are data showing the beneficial effects of omega-3 fatty acids, vitamin B6 and magnesium, vitamin C, vitamin A, vitamin B12 and folic acid, iron and zinc. However, the data are not strong and in some cases contradictory.

Feingold Diet and autism

Feingold Diet aims to eliminate all preservatives, dyes, flavor enhancers, and other similar additives from the diet. It has not been investigated so far whether this diet can bring healing effects to people with autism spectrum disorders, but research indicates that it can help children with ADHD (cited: Lilienfeld 2005). If a child with ASD therefore suffers from hyperactivity, it is possible that the Feingold diet will alleviate these symptoms.

The Specific Carbohydrate Diet and autism

I left this diet for the end, because I did not find any data indicating the effectiveness of this diet in the treatment of autism spectrum disorders. The only publication I have found on this subject is Gottschall (2004) published in the pseudoscientific journal Medical Veritas. According to Gottschall’s thesis, the digestive system of people with autistic disorders does not completely digest most carbohydrates and some proteins, and undigested food remains become a breeding ground for microorganisms whose population grows to excessively large, harmful sizes. The Specific Carbohydrate Diet assumes the intake of simple sugars, the decomposition of which will not cause a problem and thus the microorganisms will be deprived of the energy supply.

The Specific Carbohydrate Diet does not allow grains, processed foods, starchy vegetables (e.g. potatoes), canned vegetables, flour, sugar or any other sweeteners other than honey and saccharin, and dairy products, except for homemade yoghurt but only from the book by Gottschall ;)

References

Elder J., Shankar M., Shuster J. i in. (2006). The Gluten-Free, Casein-Free Diet In Autism: Results of A Preliminary Double Blind Clinical Trial. Journal of Autism and Developmental Disorders, 36(3), 413-420.
Elder J. (2008). The Gluten-Free, Casein-Free Diet in Autism: An Overview With Clinical Implications Nutrition in Clinical Practice, 23(6), 583-587.
Evangeliou A., Vlachonikolis I., Mihailidou H. i in. (2003). Application of a Ketogenic Diet in Children With Autistic Behavior: Pilot Study. Journal of Child Neurology, 18, 113-118.
Genuis S., Bouchard T. (2010). Celiac Disease Presenting as Autism. Journal of Child Neurology, 25(1), 114-119. (pdf at surefoodsliving.com)
Gottschall E. (2004). Digestion-gut-autism connection: the Specific Carbohydrate Diet. Medical Veritas, 261-271. (pdf at pecanbread.com)
Hozyasz K., Grylicka H., Żółkowska J. (2010). Dieta bezglutenowa a leczenie zaburzeń ze spektrum autyzmu – skrótowy przegląd piśmiennictwa. Przegląd Gastroenterologiczny, 5(4), 195–201. (pdf at termedia.pl)
Jackson J., Eaton W., Cascella N. i in. (2012). Neurologic and Psychiatric Manifestations of Celiac Disease and Gluten Sensitivity. Psychiatric Quarterly, 83(1), 91-102. (text at nih.gov)
Kawicka A., Regulska-Ilow B. (2013). How Nutritional Status, Diet and Dietary Supplements Can Affect Autism. A Review. Roczniki Państwowego Zakładu Higieny, 64(1), 1-12. (pdf at agro.icm.edu.pl)
Lilienfeld S. (2005). Scientifically Unsupported and Supported Interventions for Childhood Psychopathology: A Summary. Pediatrics, 115(3), 761-764.
Mari-Bauset S., Zazpe I., Mari-Sanchis A. i in. (2014). Evidence of the Gluten-Free and Casein-Free Diet in Autism Spectrum Disorders: A Systematic Review. Journal of Child Neurology, 29(12), 1-10. (pdf at researchgate.net)
Mulloy A., Lang R., O`Reilly M. i in. (2009). Gluten-free and casein-free diets in the treatment of autism spectrum disorders: A systematic review. Research in Autism Spectrum Disorders, 4(3), 328-339. (pdf at researchgate.net)
Pavone L., Fiumara A., Bottaro G. i in. (1997). Autism and Celiac Disease: Failure to Validate the Hypothesis That a Link Might Exist. Biological Psychiatry, 42, 72-75.
Pennesi C., Cousino-Klein L. (2012). Effectiveness of the gluten-free, casein-free diet for children diagnosed with autism spectrum disorder: Based on parental report. Nutritional Neuroscience, 15(2), 85-91.
Ruskin D., Svedova J., Cote J. i in. (2013). Ketogenic Diet Improves Core Symptoms of Autism in BTBR Mice. Plos One, 8(6), 1-6. (text at plos.org)
Whiteley P., Rodgers J., Savery D. i in. (1999). A gluten-free diet as an intervention for autism and associated spectrum disorders: preliminary findings. Autism, 3(1), 45-65. (pdf at drperlmutter.com)
Whiteley P., Haracopos D., Knivsberg A. i in. (2010). The ScanBrit randomised, controlled, singleblind study of a gluten- and casein-free dietary intervention for children with autism spectrum disorders. Nutritional Neuroscience, 13(2), 87-100. (pdf at mjrigtigkost.dk)