Parents and loved ones of individuals with autism know only too well that autism often goes hand-in-hand with picky eating. Children and adults with autism may exhibit strong food preferences and aversions, making it difficult to give them a nutritious diet. This is a vicious cycle, because various nutrient deficiencies, suboptimal digestive function, and gastrointestinal problems—which many individuals with autism also exhibit—may exacerbate the behavioral aspects of the condition. A range of different dietary interventions has been proposed as nutritional therapy for autism, but the effects appear to be as varied and heterogeneous as people with autism, themselves. What works well for one child or adult may make little difference for another. Some approaches, however, are a bit more promising than others. Here, let’s look at the gluten-free/casein-free diet, and the ketogenic diet.

Gluten-Free/Casein-Free Diet (GFCF)

Interest in GFCF diets for autism spectrum disorders (ASD) is based in the possibility that opioid activity from gluten and casein peptides (e.g., gluten exorphins and casomorphin) may play a role in the pathogenesis of ASD. This may be especially true in cases where increased intestinal permeability (“leaky gut”) is a factor, owing to the proposed “gut-brain-behavior axis.”

Anecdotal reports from parents of children with ASD support a beneficial role for the GFCF diet, but the majority of reviews and analyses of relevant trials come to lukewarm conclusions about the potential for benefit.

A 2018 systematic review that identified 6 suitable RCTs of GFCF diets in children with ASD found that in some cases, the diet was associated with improvements in communication and social interaction, but results from individual trials were mixed. This led the researchers to conclude that there is “little evidence” that GFCF diets are beneficial for children with ASD.

However, there may be some people for whom the GFCF approach is effective, so it should not be dismissed out of hand without even trying it. It may be worth trying an “n=1” experiment to see if removing gluten and casein from the diet has any positive impact. According to a survey from the UK, 20-29% of parents of children with autism who had implemented a GFCF diet reported “significant improvements” in core dimensions of ASD. However, the researchers noted that much of the research in this area is highly flawed and that “evidence to support the therapeutic value of this diet is limited and weak.” Of course, if an individual is identified as having a demonstrable gluten or casein sensitivity, that would clearly warrant this kind of elimination diet.

A study based on a parental questionnaire found that among children with ASD who also had GI symptoms, food allergy diagnoses, and suspected food sensitivities, strict implementation of the GFCF diet resulted in greater improvement in ASD behaviors, physiological symptoms, and social behaviors compared to changes in children whose parents reported them having none of these symptoms.

The GFCF diet is not effective across the board. Like so much in nutritional research, some people respond favorably and others do not. A double-blind, placebo-controlled challenge study that involved elimination and reintroduction of gluten and casein among 3-5-year-old children with autism found no statistically significant effects on measures of physiologic functioning, behavior problems, or autism symptoms, leading the authors to conclude that there was not enough evidence to support general use of the GFCF diet. Reviews looking at GFCF diets or diets that are only gluten-free generally come to similar conclusions: a subgroup of patients might respond favorably to these interventions, but there’s not enough evidence to institute an across-the-board recommendation for this kind of intervention for individuals with autism.

Promising findings were seen when the intervention went a little further. A randomized controlled trial of a GFCF diet that was also soy-free and supplemented with a vitamin/mineral formula, carnitine, essential fatty acids, digestive enzymes, and also called for Epsom salt baths, found that this intervention improved autism symptoms, non-verbal IQ and other symptoms in most subjects.

Ketogenic Diet

Interest in the ketogenic diet for type 2 diabetes and metabolic syndrome is exploding, and this very low carbohydrate approach shows promise in other areas, such as Parkinson’s and Alzheimer’s diseases. It’s also being explored for ASD, prompted by the overlap between autism and seizures, and the possibility that autism may have neurological underpinnings. Mitochondrial dysfunction and impaired cellular energy generation may also be a factor in autism, which would make the ketogenic diet (KD) an attractive therapeutic possibility.

This is a new area of research, so findings are preliminary but promising. A case report of a 6-year-old with high-functioning autism and subclinical epileptic discharges who had responded poorly to several behavioral and pharmacological treatments showed the child to have substantial improvements in several ASD aspects as soon as one month into the ketogenic diet, with the improvements continuing throughout the end of the observation period at 16 months. (It’s noteworthy that the child was shown to have reduced brain glucose metabolism as measured via PET scan. This is a defining hallmark of Alzheimer’s disease, another condition that may respond favorably to the ketogenic diet.)

A larger study tested the effects of a gluten-free ketogenic diet supplemented with MCT oil in 15 children with autism (ages 2-17). The diet called for a maximum of 25g net carbohydrates, protein calculated based on the subjects’ weight (allowing for up to twice the RDA for protein), and the remainder of energy from fat, with 20% of total energy coming specifically from MCTs, either from coconut oil or MCT oil. After 3 months on the diet, 6 subjects had “substantial improvement” in various ASD measures, two had “moderate improvement,” and seven had minor or no improvement. Improvements were mixed over different parameters, such as social aspect and repetitive behavior; the diet did not improve all measures equally. Interestingly, patients with seizures or a history of seizures were excluded from the study, so whatever mechanisms may be responsible for the improvements appear to be unrelated to mechanisms of seizure control from ketosis.

A larger study, this one involving 45 children ages 3-8 with ASD, compared the effects of a GFCF diet, a KD, and a control diet of “balanced nutrition.” After 6 months, both intervention groups showed significant improvement in various ASD measures, but the KD group scored better in cognition and sociability compared to children on the GFCF diet. (The KD was implemented as a modified Atkins diet, which calls for a higher protein intake than a classical KD.)

Both of these dietary interventions show efficacy in some subjects, but not all. There’s only one way to test a diet, and that’s to do it. If it’s effective to any extent for an individual with autism, the family or caregivers can decide if it’s worth continuing, and if it’s not effective, the nice thing about a dietary intervention is that it can be stopped at any time. Unlike a surgical procedure, diets are not permanent, and if someone is unhappy with their results, they can simply return to their previous way of eating.