A new review of more than 150 research papers reveals that scientists have been reporting links between the composition of gut bacteria and autistic behaviors since the 1960’s. Many of these studies suggest that restoring a healthy balance in gut bacteria can treat symptoms of autism spectrum disorder (ASD).
The findings, published in the journal Frontiers in Cellular Neuroscience, provide strong evidence for initiating large-scale studies that will look into altering the composition of gut bacteria in people with ASD. Until now, ASD treatments have involved rehabilitation, educational interventions, and medication.
“To date there are no effective therapies to treat this range of brain developmental disorders,” said Dr. Qinrui Li of Peking University, China. “The number of people being diagnosed with ASD is on the rise. As well as being an expensive condition to manage, ASD has a huge emotional and social cost on families of sufferers.”
People with ASD have long reported gastrointestinal problems, such as diarrhea, constipation, and flatulence. Researchers believe that the root of these problems may be an imbalance of “good” and “bad” bacteria in the gut.
Many of the studies included in the review support the idea of a gut-brain axis, biochemical signaling that occurs between the gastrointestinal tract and the central nervous system.
For example, overgrowth of bad gut bacteria will most likely result in an overproduction of by-products, including toxins, which can make the gut lining more permeable. Then these toxins, by-products, and even undigested food can get into the bloodstream and travel to the brain.
In very young children, whose brains are at the peak of development, the presence of these chemicals can impair neurodevelopment, leading to ASD.
“ASD is likely to be a result of both genetic and environmental factors,” said Li. “The environmental factors include the overuse of antibiotics in babies, maternal obesity and diabetes during pregnancy, how a baby is delivered and how long it is breastfed. All of these can affect the balance of bacteria in an infant’s gut, so are risk factors for ASD.”
However, the review also showed strong evidence that reverting the gut microbiota to a healthy state can reduce ASD symptoms.
“Efforts to restore the gut microbiota to that of a healthy person has been shown to be really effective” said Li. “Our review looked at taking probiotics, prebiotics, changing the diet — for example, to gluten- and casein-free diets, and fecal matter transplants. All had a positive impact on symptoms.”
Improvements included increased sociability, a reduction in repetitive behavior, and improved social communication in people with ASD.
While the review findings are very positive, the researchers believe that the studies are too few and too small, and that new clinical trials are needed to take this research to the next level.
“We are encouraged by our findings, but there is no doubt that further work needs to be carried out in this field” said Li. “We need more well-designed and larger-scale studies to support our theory. For now, behavioral therapies remain the best way to treat ASD. We would hope that our review leads to research on the link between the gut microbiota and ASD, and eventually a cheap and effective treatment.”