An altered microbiome has been linked to a large number of human diseases – and thus either implicitly or explicitly as a partial cause of -. These include immune diseases like Celiac disease, asthma, and diabetes; obesity; Crabs; psychiatric disorders like depression and Alzheimer’s disease; and Autism Spectrum Disorders (ASD). It was connected with so many things that Jonathan Eisen was compelled to do that “Overselling the Microbiome Awards. “ He took years to make the list, despite being an evolutionary biologist who really recognizes and understands the critical role our microbiome plays in our health.
The idea that an altered microbiome can be a causative factor for ASA stems from studies with mice in which the transfer of the intestinal flora from people with ASA to mice led to social deficits and behavioral problems in the animals. But evidence in humans struggled, so a group of Australian scientists who shared Eisen’s caution, led by Jacob Gratten, decided to put the idea to a rigorous test.
A replication bug
Knowing that ASA is often linked to gastrointestinal symptoms, the Australian team realized that it is tempting to look for and even embrace a gut component of the condition. However, they find that the human studies linking an altered microbiome to ASD are quite weak: they’re small, they’re biased and don’t take into account confounders, and they’re poorly designed and analyzed. In addition, the researchers write: “A meta-analysis of animal studies related to the human microbiota has raised concerns that the extent of the positive results is implausible.”
So they did their own study and looked at the microbiome of 247 children. Of those examined, 99 had ASA, 51 were healthy siblings, and 97 were unrelated children without a diagnosis of ASA. They found “negligible evidence of direct associations between the stool microbiome and the diagnostic status of ASD”. They also “failed to replicate previously reported ASD-gut-microbiome associations” and identified only one species (out of 607 examined) that differed significantly in frequency between children with and without ASD.
They found that the different composition of the microbiome correlated with diet. Children with ASD had a significantly reduced nutritional variety. This could be due to ASD-associated allergies or GI symptoms, or because children with ASD may have strong sensory likes and dislikes. Food and meal times can also become a battlefield / focal point / opportunity to wield power, and parents just may not have the energy to argue about it (ok, that may be the case with Everyone Children, not just children with ASD).
(Parents could also use diets to moderate their children’s behavior. I spoke to a mother – not in this study – whose child only ate pears, frozen waffles, and a certain type of smoked chicken that she had to buy every third day. This was approved by a nutritionist. When I asked her if she thought it would help and make her child better, she replied, “I wouldn’t do it any other way.”)
Reversal of causality
So this study concludes that children with ASD have reduced dietary diversity due to their behavior, and this changes the taxonomic makeup of their microbiome. However, the authors point out that it is still possible for the microbiome to then influence children’s behavior in a feedback loop.
ASD is a very complex disease with very complex etiologies. The authors point out that based on studies with mice it already exists clinical studies aimed at Treat ASA by targeting the microbiome. However, they suggest that working on diversifying the children’s diets could be a better course of action, as it could affect their behavior, microbiome, and overall health – although it may not be an easy path for parents and caregivers to do.
In any case, they warn that we may want to reverse our thinking about the relationship of the microbiome to other psychiatric illnesses. Instead of assuming that the microbiome affects behavior, it may be that behavior – that is, diet – affects the microbiome.
Cell, 2021. DOI: 10.1016 / j.cell.2021.10.015
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