A group of scientists is challenging the popular idea that gut bacteria play a role in causing autism.
In a new opinion article published in the journal Neuron, the researchers argue that there is no solid scientific evidence linking the gut microbiome to autism.
They believe the idea has been supported by weak studies with poor methods, small groups of participants, and flawed reasoning.
Kevin Mitchell, a developmental neurobiologist from Trinity College Dublin and the lead author of the article, said, “Despite what you’ve heard, read, or watched on Netflix, there is no evidence that the microbiome causally contributes to autism.” He added that autism is mainly caused by genetic factors and that more research should focus on genetics.
So why do some people still believe gut bacteria could be involved? The idea first came about because many people with autism also have stomach and digestion problems. At the same time, more children have been diagnosed with autism in recent years.
Some people think this rise must be due to environmental or behavioral changes. But the researchers explain that this increase is more likely due to greater awareness and broader definitions of autism, not because something in the environment is causing it.
Researchers have tried to explore the link between the gut microbiome and autism in several ways.
They’ve compared the gut bacteria of people with and without autism, studied mice with autism-like traits, and tested treatments like probiotics or fecal transplants in people with autism. But the scientists behind this new paper say none of those studies have given convincing evidence.
Dorothy Bishop, a developmental neuropsychologist at the University of Oxford and a senior author of the article, said that the results from those studies are all over the place and don’t form a clear picture.
One of the biggest problems, the team says, is that many studies used very small groups of people—sometimes only 7 to 40 per group. This is too few to get reliable results, especially since autism is not rare.
According to Darren Dahly, a biostatistician from University College Cork and another co-author, studies should include thousands of participants for trustworthy conclusions.
Another issue is that the studies used different methods to study the gut microbiome, making it hard to compare results. And even when differences were found between people with and without autism, the results often didn’t agree.
Some studies said people with autism had less variety in their gut bacteria; others said the opposite. And when other factors like diet were taken into account, the differences often disappeared.
Mitchell explained that it may actually be the other way around—having autism can affect what someone eats, which can then change their gut bacteria.
Studies using mice also have problems. Mitchell said that mouse behavior labeled as “autistic-like” doesn’t really match what autism looks like in people. Plus, the studies had other scientific flaws.
Some human clinical trials have tested whether changing the gut bacteria through probiotics or fecal transplants could improve autism symptoms. But the new paper says most of these trials had weak designs. Many didn’t include control groups or proper randomization. And when the trials were done properly, they showed no effect.
Because of this, the researchers believe it’s time to move on from the theory that gut bacteria cause autism. Bishop said, “If you accept our message, there’s two ways you can go.
One is to just stop working on this area, which is something that we would be quite happy to see. But given that realistically, people are not going to stop, they need to at least start doing these studies in a much more rigorous way.”
If you care about autism, please read studies about a new cause of autism, and cats may help decrease anxiety for kids with autism.
For more information about health, please see recent studies about vitamin D that may hold the clue to more autism, and results showing strange eating habits may signal autism.
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