Is autism related to microbiota?

There are very few studies, and virtually none in adults, that discuss the relationship between microbiota and autism. There are some studies in children, but nothing conclusive about them.

One of the things observed in these studies we're talking about is microbiota alterations in people with autism. But we must keep in mind something very important: we're talking about population groups that, for the most part, have many dietary restrictions. This is due to hypersensitivities or rigidity. What happens with these alterations observed in the microbiota of autistic children is that it's not clear whether they are a cause or a consequence. That is, whether autistic people truly have microbiota alterations related in some way to the onset of autism, or whether it's due to the alterations in autism, rigidity, a reluctance to try new things, or because they only eat certain foods due to their sensory difficulties, the result is an altered microbiota.

But perhaps if we start by describing what autism and microbiota are, you can better understand what we're talking about. In clinical settings, we always refer to autism as a disorder, but it's also true that we understand that there is a portion of the population that may have autistic symptoms or clinical manifestations without becoming dysfunctional. But as such, the autism spectrum is a neurodevelopmental disorder that basically manifests itself through difficulties in communication and social interaction. Furthermore, people on the autism spectrum often present a series of more restrictive and repetitive patterns, activities, and ways of functioning. Translating this into understandable language , these would be people with difficulties, especially in social relationships and communication. On the other hand, these are people who often have slightly more obsessive or restricted interests, a slightly less flexible way of functioning. In other words, the altered aspects in autism are closely related to sensory issues.

Regarding the microbiota, what we're talking about in this case is the microbiota of the digestive tract, but the microbiota is the set of bacteria that colonize the skin, the digestive tract, including the mouth, and also the genital tract. It's very important to understand that the bacteria that make up the microbiota aren't necessarily pathological; some can be, but many of them aren't. For example, many of them aid in digestion and also protect us from many things, help maintain the immune system , or regulate metabolism and energy balance.

We're talking about a series of microorganisms that coexist with us and with which we exist in a symbiosis and homeostasis. What happens, and what is increasingly being studied, is that these symbiosis and homeostasis sometimes become deregulated, and alterations or diseases can then arise.

Regarding the relationship between microbiota and autism, we found that many of the published scientific articles have methodological flaws because they don't describe the individual's dietary profile, making it impossible to accurately interpret their results . You can roughly interpret this as true, it seems there could be a different profile. But you should also know that the altered microbiota observed cannot be classified as better or worse than that of people without autism; it simply appears to be different.

Another issue that has been extensively studied is whether alterations in the microbiota are related to worse autistic symptoms—that is, whether these alterations can cause more autistic symptoms—but these studies have not yielded conclusive results either. Results have been seen in people with autism and altered microbiotas who were given probiotics, perhaps slightly improving their gastrointestinal function, but there are no studies to date that conclude that treating microbiota-related issues with probiotics improves autism symptoms.

What is indisputable is the importance of the gut-brain axis. At our hospital, we are studying the microbiota in relation to autism, attention deficit disorder, depression, and schizophrenia. In other words, everything that happens in our microbiota can probably influence mental health, but we don't yet know how.

For all these reasons, the recommended diet for people on the autism spectrum is the Mediterranean diet. We mean that it is not scientifically justified to eliminate any product , be it gluten, lactose, or any other, from the diet of autistic people, unless the person has an intolerance or allergy to those specific foods.

Laura Gisbert holds a PhD in psychiatry, is a professor and researcher at Vall d'Hebron University Hospital, and is the coordinator of the Comprehensive Care Program for Autism Spectrum Disorders at the Mental Health Service at the same hospital.

María Martínez Ramírez is a specialist in adult, child, and adolescent psychiatry. She works in the Comprehensive Care Program for Autism Spectrum Disorders at the Mental Health Service at Vall d'Hebron University Hospital.

Question sent via email by Juana C Fernández .

Coordination and writing: Victoria Toro .

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The advice in this clinic is general in nature and does not replace medical advice. If you have questions about your specific problem, please consult your healthcare professional.