The problems related to the digestive system in autism have a great relevance, given the negative impact they generate on the quality of life of the person and the behavioral manifestations that it generates. From constipation to diarrhea, eating disorders, associated behavioral problems, and a large number of effects that have generated even all kinds of theories, which are more strange, about intervention models in people with autism.
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There are several important factors that we must consider, already in the article " Autism, childhood and digestive problems " (1) we highlighted the fact that the prevalence of gastrointestinal functional disorders as a reason for consultation in the pediatric age is very high and they would represent around 10% of primary care consultations and up to 50% of pediatric gastroenterology visits, this in relation to the general pediatric population. That is, digestive problems are quite common, although in the population with autism spectrum disorders (ASD) their impact seems to be greater, mainly in family reports. And this situation has generated an immense volume of studies on alterations of the digestive system and autism, being at present the study of the intestinal flora one of the fields of greater relevance, although not only in the clear autism.
We know that the quality of our intestinal flora (or microbiota) is fundamental for the processing of nutrients, and that poor quality of this flora has a negative impact on health. In this regard there is a growing base of studies that are influencing the importance that this type of alterations of the flora generates in digestive health and its relationship with behavioral and even brain aspects.
A study published in February tells us about Clostridium difficile infections (2) , this study is a systematic review of infections caused by this bacterium and its impact on the health of the person. In this case ctriatridium difficile is the main cause of diarrhea associated with antibiotics. In the case of children with autism, it is common to find recurrent ear infections that are treated with antibiotics (In some cases, this type of otitis may be linked with alterations in the maxillo-facial, oral and pharyngeal area). This antibiotic treatment can cause an imbalance of our intestinal flora. In this case they tell us about the efficacy of the use of probiotics as a form of intervention. Although he notes that much more research is still needed, this study found that probiotic supplementation is a valuable adjunct in the routine care of patients receiving antibiotic therapy.
Another study published in the journal Cell (3) tells us about Lactobacillus reuteri and its impact on social relationships, the study was conducted in mice. The absence of Lactobacillus reuter i caused a deficit in their social behavior in mice.
" Other research groups are trying to use drugs or electrical brain stimulation as a way to reverse some of the behavioral symptoms associated with neurodevelopmental disorders, but here they have, perhaps, a new approach, " says the lead author. , Dr. Mauro Costa-Mattioli, Associate Professor of Neuroscience at Baylor. " We do not know yet if it will be effective in humans, but it is a very interesting way of affecting the brain from the intestine, " he adds.
Mauro Costa-Mattioli and colleagues from the Baylor College of Medicine explain a possible link through the gut microbiome in this video.
For starters, the researchers fed approximately 60 female mice with a high-fat diet that was the approximate equivalent of consistently eating fast food several times a day. They fed the mice and waited until they were young. The offspring stayed with their mother for three weeks and then were weaned to a normal diet. After a month, these pups showed behavior anomalies, such as spending less time in contact with their peers and not initiating interactions.
"First we wanted to see if there was a difference in the microbiome between the children of mothers of mice fed a normal diet, compared to mothers fed a diet high in fat. Therefore, the sequencing of the gene encoding the 16S ribosomal RNA was used to determine the bacterial composition of its intestine. We found a clear difference in the microbiota of the two groups, says lead author Shelly Buffington, a postdoctoral fellow at Costa-Mattioli's lab: " The sequencing data were so consistent that looking at the microbiome of an individual mouse we could predict whether its behavior It was deteriorating . "
Previous studies showed that Lactobacillus reuteri increases oxytocin levels. The results suggest that even the maternal diet can affect the social behavior of their offspring (at least in mice) and adds to the growing scientific literature that shows the microbiome or intestinal flora as a basic actor in behavior.
Although we still do not adequately understand the communication between the intestinal microbiota and the brain, we know that there are bidirectional aspects, as well as the direct mediation of the vagus nerve between the brain and the intestine. Similarly, the stimulation of the immune system and brain function have various links. According to Buffington, " There have been many recently published works that show the existence of a bidirectional communication between the intestine and the brain. This communication channel is colloquially called the "gut-brain axis". Epidemiological studies in humans have shown that maternal obesity increases the risk of neurodevelopmental disorders in offspring. The same has been found in non-human primates . "
" There is increasing evidence that the microbiome, especially early in life, can have long-term effects on brain development and behavior, " said anatomist and neuroscientist John Cryan, of University College Cork in Ireland, who did not participated in the study. " What this work does is take advantage of the fact that we have our mothers' microbiome, and see what happens if the mother disturbs her microbiome during pregnancy ."
A study from 2011 (4), where they also worked with mice to which they gave diets that were supplemented with Lactobacillus rhamnosus , a bacterium commonly found in diet supplements with probiotics, experienced a reduction in stress and anxiety. The bacteria also appeared to cause a redistribution of brain receptors for the neurotransmitter GABA (γ-aminobutyric acid).
Another study (5) published in the British Journal of Nutrition, where rats (not mice, rats have a larger size and weight) and humans were treated, where stress, anxiety and stress reduction were evaluated. depression through the consumption of probiotics, specifically Lactobacillus helveticus R0052 and Bifidobacterium longum R0175 were used. The results in both rats and humans showed a reduction of these factors, showing that the use of this type of compounds can be useful in the treatment for the reduction of stress, anxiety and depression.
Another study, also published in the journal Cell in 2013 (6) again focuses on the alterations of the digestive system in autism and its interactions with the intestinal flora, as well as the effects on the level of the immune response and alterations in the microbiota of people with autism. In this study, the researchers used genetically modified mice to which they gave a treatment with Bacteroides fragilis , after the administration of the probiotic it was observed that the intestinal function was corrected and then some behaviors associated with autism were regulated, mainly with regard to communication , sensorimotor aspects and repetitive behaviors. They also observed a regulation of intestinal homeostasis as well as a regulation of the levels of Lachnospiraceae (a bacterium of the Clostridia family ).
At the annual meeting of the American Society for Microbiology , which met in Boston (USA) last May, Philip Strandwitz and colleagues from Northeastern University in Boston presented their work (7) on a species of intestinal bacteria recently discovered , call s KLE1738, which are able to grow and reproduce only in case of being fed with the molecules of γ-aminobutyric acid (GABA). In fact, Strandwitz explains that nothing served to grow these bacteria, except GABA. Recently, another team of scientists found the brain chemistry altered in people with autism (8) , where the impact on the sensory level of this alteration was discussed. And we see how the GABA again appeared previously mentioned in this same article referred to the Lactobacillus rhamnosus , that although it does not feed on GABA if it seems to alter it. The effect of these bacteria, KLE1738, is to impact the mood of the affected person. The modulation of GABA by the intestinal microbiome could be one of the channels of communication of the gut-brain axis, according to the researchers.
It should be noted that people with autism and eating disorders are much more susceptible to having this type of intestinal flora alterations. There seems to be a direct relationship between eating disorders and alterations of the digestive system, although it is not clear what causes what, if the eating disorder causes the digestive alteration or vice versa. The alterations of the intestinal flora are usually common in people with obesity or chronic problems of the digestive system and also in person with anorexia or bulimia .
However, we must be cautious about this data. It is obvious that eating disorders are related to alterations of the intestinal flora, that there seem to be certain concomitant factors at a genetic level, related in some cases with autoimmune or even environmental aspects. But not all people will fit 100% in the cases shown in the studies shown here. Nor is it a good idea to immediately administer uncontrolled probiotics to a child with autism while waiting for it to improve substantially. But we can conclude that the aspects related to the quality of our microbiota or intestinal flora play a fundamental factor in our health, as well as the related effects between the digestive system and brain aspects, although this relationship is not clear to this day. It is important to continue investigating.