The cause of autism, and its dramatic rise in prevalence, remains an enigma. Today, one in 150 eight year olds in the United States has autism, compared to one in every 2,000 four decades ago. The disorder likely has a number of causes that involve both genes and environment, or a combination of the two.

Dr. Emeran Mayer, a gastroenterologist and neurologist, suggests it's possible there's a brain-gut connection.

Read More: Autism Cause Theories 2016

In Big Think's video, "Could Autism Be Caused by Gut Microbes?" Mayer explains the majority of autistic children have digestive problems, including constipation, abdominal pain, and discomfort. Part of this likely has to do with diet, or the unique eating habits of autistic kids. Fiber and fermented foods are excluded from the diet, leaving some to wonder why kids would select such a diet.

Mayer believes it has to do with the texture of foods. Things that are soft are much preferred over crunch and chewy things. Previous research has also looked at gut microbes in fecal samples from patients with autism, and have found abnormalities. Moreover, several studies have suggested many autistic people have marked differences in their microbiome compared to other people, although they haven't been consistent in pinpointing specific differences, such as the presence of any one particular bacterium or absence of another.

A 2016 study published in Cell suggests a common probiotic may ease some autism symptoms. Researchers showed restoring levels of the "good" bacterium Lactobacillus reuteri led to higher levels of oxytocin, a hormone associated with social behavior in mice. It also improved signs of brain plasticity, which is the brain's ability to form new connections that foster learning. However, it's important to remember this study was with mice. Mouse brains aren't parallel to human brains, and their microbiomes aren't the same as human microbiomes. This is why human treatments have yet to be made.

Similarly, a 2013 study associated autism-like behaviors with distinct changes in the microbiome and showed that feeding the mice Bacteroides fragilis — another beneficial intestinal bacterium — improved their sociability. The new mouse study goes further in exploring a possible explanation of how changes in bacteria influence brain development and function.

Anytime you use a probiotic, even the ones that are in commercially available products, you need to get FDA approval if you want to prove a particular yogurt with microbes is probiotic, and beneficial for a disease condition. This is a complex process, but the interest to produce this probiotic, and making it acceptable for human use, is gaining interest.

One questions remains: Can influencing the microbial composition reverse some of the changes in either gut dysfunction or cognitive and social interaction in autistic patients?

It’s not fully understood how microbiome-brain interactions influence the symptoms of autism, but it’s worth a second look.

See Also:

Quick Test Shows How Children With ASD Process Information Differently

Autism Spectrum Disorder May Not Develop Entirely In Human Brain