Within both the research and the clinical communities, the relationship between autism spectrum disorder (ASD) and diet has long been a topic of discussion. However, understanding the complex relationship between autism and food continues to be an ongoing challenge. This is largely because food can play a role in each of three distinct areas: the development of autism, the manifestation of symptoms, and the treatment of the condition. When considering the relationship between autism and food from each of these perspectives, it is important to examine the existing research and what it can mean for the future of autism treatment and prevention.
Food as a Contributing Factor to the Development of Autism
There is broad consensus within the research community that autism is caused by a wide range of factors, including both genetic characteristics and environmental influences. Most scientists also agree that the pathogenesis of autism begins during prenatal development. This idea has led some researchers to hypothesize that the mother’s nutritional status may be among the environmental causes of autism that interact with genetic factors to cause the development of autism. Indeed, multiple studies have established strong correlations between diet-related health conditions in the mother and a higher risk of autism in the child. For instance, both type 2 diabetes and gestational diabetes have been associated with a higher risk of autism. In addition, if the mother meets the standards for obesity, the risk of autism increases by 21.5%, and if the mother has hypertension, the risk of autism in the child rises by 14.3%.
In 2017, a researcher at UC Davis published a paper proposing a mechanism through which a mother’s diet-related health conditions may facilitate the development of autism. Based on a review of the latest research in the field, the researcher suggested that these conditions were associated with a lower intake of several key micronutrients that may be involved in the etiology of autism: zinc, copper, iron, and vitamin B9. In combination with genetic risk factors, an insufficient intake of these nutrients may contribute to disruptions in fetal brain development that lead to autism. Although future research is needed to conclusively establish a causal relationship between maternal nutritional status and autism, it is clear that the mother’s relationship with food before and during pregnancy is directly associated with the development of autism.
It is important to note that pregnant mothers who have one of these food-related health conditions can still take action to reduce the risk of autism for the child. By making strategic dietary decisions that target specific micronutrients, it may be possible to reduce autism risk. Studies in animal models have also shown that taking supplements of certain micronutrients can effectively reduce autism risk. In the future, clinical trials in humans may make it possible to identify the most effective food and nutritional supplement choices for expectant mothers who are concerned about autism.
Food-Related Issues as a Manifestation of Autism
While the discussion of food as a potential cause of autism remains primarily within the research community, many patients and families experience a more concrete connection between food and autism on a daily basis. Put simply, children with autism are significantly more likely to be “selective” or “picky” eaters. According to one estimate, about 25 percent of healthy children are picky eaters, while about 80 percent of children with autism demonstrate selective eating tendencies, often refusing to eat (or even try) whole categories of foods. In the most serious cases, a child with autism may limit their diet to as few as five foods.
One of the proposed explanations for the increased incidence of selective eating among patients with autism is their heightened sensory sensitivity. According to some estimates, about 90% of children with autism process tactile, olfactory, visual and auditory information differently than normally developing children. Based on these statistics, it should come as no surprise that preferences regarding the taste, texture, smell, and even appearance of food are evident in patients with autism.
Unsurprisingly, studies also show that selective eating issues in patients with autism can lead to deficiencies in important micronutrients—especially among the patients with the most restrictive diets. While specific nutritional deficiencies are likely to depend largely on a child’s individual food restrictions, a broad study of over 250 children with autism from five different US states highlighted insufficient consumption of vitamin A, vitamin C, zinc, phosphorus, fiber, choline, calcium, vitamin D, and potassium. Although the commonness of inadequate intake is just as high among normally-developing children as patients with autism for some of these nutrients, the effects on patients with autism may be more significant. For instance, evidence suggests that certain nutrients are less readily absorbed by patients with autism. As a result, the problem can escalate from inadequate intake to measurable nutrient deficiency much more quickly.
A possible explanation for why certain nutrients are less readily absorbed in patients with autism is the difference between the gut microbiome in patients with autism and their healthy counterparts. Bacteria in the gut play a key role in nutrient absorption, and studies in both human and animal models suggest that the bacterial composition of the gut is different for patients with autism. Although there are not yet results from clinical trials, modifying the gut microbiome in patients with autism to optimize absorption and minimize gastrointestinal issues is being considered as a potential therapy.
Food as a Contributor to the Escalation of Autism Symptoms
For patients with autism, food selectivity can also exacerbate other symptoms. Deficiencies in multiple nutrients, including methyl B12, vitamin D, and folic acid, have all been associated with autism etiology and the core symptoms of the disorder. Moreover, it is widely recognized within the research and clinical communities that the gut microbiome is impacted by food choices—and the health of the gut microbiome is directly related to both gastrointestinal and neurological symptoms of autism. For instance, disruptions in the gut microbiome can affect gut motility, which is a common symptom of autism. Also, in patients with Leaky Gut syndrome (which is also common among patients with autism), toxins from the microbiome can enter the bloodstream and impact the brain, potentially contributing to the neurological symptoms of autism. Because repetitive behaviors—such as selective eating—are among these neurological symptoms, abnormal food behaviors in patients autism may even be driving a vicious cycle: the more a patient restricts nutrients, the more their internal neurological processes will support a tendency toward restriction.
There is also preliminary evidence that consuming certain types of foods may directly exacerbate symptoms of autism. For example, some studies indicate that dietary gluten and casein are not properly digested in the gut of patients with autism. Not only can the resulting peptides interfere with regular bowel motility, but they can also directly affect brain functioning. In patients with “leaky gut”—a condition commonly associated with autism—partially-digested peptides may cross the intestinal barrier and build up the brain, where they can have an opioid-like effect that is associated with some of the core symptoms of autism.
Food as a Possible Therapy for Patients with Autism
Because of the associations between eating behaviors, nutritional status, and autism, a wide range of food-related therapies have been proposed by both researchers and practitioners. Some of the most popular are elimination diets, like gluten-free, casein-free, and lactose-free diets. Other dietary strategies emphasize the importance of eating more probiotic-rich foods that support the health of the gut microbiome. While small-scale studies have examined the efficacy of specific diets for patients with autism, the results are mixed. Given that selective eating patterns can vary widely between patients, it is little surprise that no single diet has been identified as the best option.
Still, some clinicians may recommend dietary strategies based on an individualized evaluation of the patient’s symptoms and needs. Improving the health of the gut microbiome can be a major goal of these dietary strategies. As previously mentioned, studies suggest that the bacterial composition of the gut may be tied to both gastrointestinal and neurological symptoms, so a doctor may recommend nutritional changes that focus specifically on the gut microbiome.
When patients are not getting the nutrition they need from food, another option is to boost micronutrient intake through supplementation. Taking supplements optimized for bioavailability can be a particularly effective strategy for patients who struggle with the sensory processing of a normal, balanced diet. Although research is still in the early stages, studies on supplements like methyl B12 and folinic acid offer preliminary evidence of behavioral improvements in patients with autism.
Clearly, the relationship between autism and food is complicated. In pregnant mothers, nutritional status can affect a child’s risk for autism. During childhood and beyond, abnormal food behaviors can manifest as a symptom of autism, and they can exacerbate other symptoms by affecting the patient’s neurological and gastrointestinal functioning. At the same time, the relationship between autism and food presents opportunities for dietary interventions that may prevent or resolve symptoms of autism. This possibility is opening up exciting avenues for research into nutritional supplementation therapies that could improve the lives of people with autism and their families.
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