There has long been an association between gut bacteria, the brain and autism. I personally have no problem thinking this is the case. However, I would be very reticent to mention my thoughts to doctors, certain friends, and even parents of autistic children. It just feels a bit too trendy, a bit too pseudo scientific and all slightly theoretical and under validated.
However, the other day I heard of an experiment that blew me away. It is called Microbial Reconstitution Reverses Maternal Diet-Induced Social and Synaptic Deficits in Offspring
In a nutshell, mice with altered gut bacteria showed autistic social behaviour patterns. Once the gut bacteria of these same mice was altered, the mice showed normal social behaviour. Or if you like more scientific detail, here is the official summary:
‘Maternal obesity during pregnancy has been associated with increased risk of neurodevelopmental disorders, including autism spectrum disorder (ASD), in offspring. Here, we report that maternal high-fat diet (MHFD) induces a shift in microbial ecology that negatively impacts offspring social behavior. Social deficits and gut microbiota dysbiosis in MHFD offspring are prevented by co-housing with offspring of mothers on a regular diet (MRD) and transferable to germ-free mice. In addition, social interaction induces synaptic potentiation (LTP) in the ventral tegmental area (VTA) of MRD, but not MHFD offspring. Moreover, MHFD offspring had fewer oxytocin immunoreactive neurons in the hypothalamus. Using metagenomics and precision microbiota reconstitution, we identified a single commensal strain that corrects oxytocin levels, LTP, and social deficits in MHFD offspring. Our findings causally link maternal diet, gut microbial imbalance, VTA plasticity, and behavior and suggest that probiotic treatment may relieve specific behavioral abnormalities associated with neurodevelopmental disorders.’ (Source)
This was a scientific study discussed on the podcast This Week in Microbiology. This is not a ‘healthy living’ podcast, but a scientific podcast. This is by microbiologists/ virologists, for microbiologists (and a few weirdos like me!). Honestly these people are not yoghurt eating traditional foodies, they are pretty rational, straight down the line scientists. They were fascinated by the findings of this study and impressed by the general scientific approach. I am not a scientist so I am grateful to be able to leapfrog onto their analysis of the study.
The experiment was inspired by the awareness that obese mothers are 1.5 times more likely to have children with neuro developmental disorders such as autism spectrum disorder than mothers with a ‘normal’ BMI. So one generation of mice were fed excessive amounts of fat which led them to become obese. Their children were then fed a normal diet, leading them to have a normal weight. However, even though they looked the same as the control mice, they were much more likely to display unusual social interaction and sociability patterns. The ‘normal’ mice displayed a preference for social novelty whereas the test mice showed no preference. Thus they would not distinguish between whether they wanted to be with mice they knew or any old mice. Apart from opening my eyes to the surprising complexity of mice relations (!), this mirrors some of the social symptoms of autism in humans.
Those conducting the experiment then wished to explore if gut bacteria has a roll in the changed pattern of social interaction. Checking the actual gut bacteria of these mice would probably mean sacrificing them, so they checked their fecal biome (Ie pooh!). The children of the obese mice were found to have dysbiosis, a much more limited range of gut bacteria. In particular, they seemed to be particularly low in the bacteria Lactobacillus reuteri.
The gut bacteria of the mice was then altered. This is an easy process as mice eat each other’s ‘waste’. Amazingly the mice then displayed entirely normal social behaviour.
All of this suggests very strongly that there is a definite link between gut bacteria and autism spectrum disorder. Oxytocin Seems to be the hormone which is stimulated by the lactobacillus reuteri. Since this is produced in the brain, in the hypothalamus, it seems that there is some way of communicating between the gut and the brain. Other experiments strongly suggest that the Vegas nerve may be the pathway.
I love the comments from the Microbiology Today guys:
In all the microbiome papers we’ve done their are enormous implications of these bacteria that we live with. They seem to control almost every aspect of our lives. Proving that is hard.
Regarding autism, this one bacteria doesn’t seem to offer a wonder cure. It does not ‘cure’ repetitive behaviour also associated with autism. It is probable that other bacteria may affect other associated symptoms and there will also be a cluster of other associated causes. However, this link is really profound. It suggests that looking after your gut bacteria really is a good priority to have. Eat up your cultured dairy and fermented foods, dear reader!
Knowing about this experiment is also going to make me a little bit more confident about possibly saying something to a mum of an autistic child about the link between autism and the health of the gut. I will still couch what I say with plenty of possiblies and maybes, as I would not want to wade too strongly into a sensitive area, but this may tip me into at least saying something.