Reacción a "Reactions: two studies link microbiota composition to depression"

These studies provide confirmation of an existing hypothesis that other authors had previously explored, namely the possibility that people with depression may have a different microbiota. Both studies have been published in a high impact journal and this is due to the high number of cases included. This is the most important thing that these studies provide. The methodology is the usual one used to study differences in gut microbiota composition.  

The implication of this work is that we should add the gut microbiota as another factor in the cause of depression. It is suggested that it is an organic cause related to the production/degradation of neurotransmitters by bacteria in the intestinal tract. Although these theories have been around for some time, the study of the microbiota has not yet been incorporated into clinical practice, also because the tools we have to modulate it are scarce. At the moment we cannot use antibiotics because of the high resistance pressure, probiotics are of doubtful use and faecal transplantation is not authorised for this type of pathology.  

The biggest problem with this work is that it is based on the composition of the microbiota. From the data obtained, the production/degradation of neurotransmitters is inferred, but the concentration of these neurotransmitters in faeces or serum, which would be essential to prove it, has not been determined. All these studies rely on faecal DNA to determine the composition of the bacteria and from this data the functionality of the bacteria is inferred, but the final metabolome needs to be known.