Reacción a "Reactions: two studies link microbiome changes to chronic fatigue syndrome"

These two studies investigate changes in the faecal microbiome and blood plasma metabolome associated with chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME). One is the first study to differentiate between recent illness (diagnosed within the last four years) and long-term illness (diagnosed more than ten years ago), providing insight into how disorders of the microbiome progress when the disease is established. The two studies are consistent in several respects, including the detection of a decrease in gut biodiversity and in the abundance of butyrate-producing bacteria, an anti-inflammatory metabolite with a known beneficial effect on the intestinal epithelium. 

Both studies are of good quality and use high-resolution techniques - shotgun metagenomics, which looks at the whole genome, as opposed to previous studies based on 16S single gene analysis. The analyses are correct and use validated approaches. Both studies have their limitations, as the authors themselves acknowledge. One limitation is the small sample size, especially considering the heterogeneity of the symptoms of this syndrome. Also, such studies provide correlations, not cause-effect relationships, as the authors acknowledge, and further research is needed. For example, differences between the diets of different groups could explain some differences in the composition of the microbiota. However, the congruence between the two studies reinforces the validity of the suggested relationships. 

These studies shed light on a syndrome whose causes are unknown. The study does not establish the causes, as we have said, but it allows us to establish some hypotheses on how it may become established in the long term through a disturbance of the intestinal balance that becomes chronic. I think we are still far from understanding this process. It is possible that the alterations detected are responsible for some of the symptoms of the disease, especially those related to digestive functions. And if so, interventions on the microbiome using probiotics, prebiotics or dietary changes could alleviate some of these symptoms, which would increase the quality of life of patients. 

Another result included in both studies is the diagnostic potential that analysis of the faecal microbiome can have. Using artificial intelligence techniques, they detected microbial patterns that allowed them to distinguish between healthy people and patients with the syndrome. However, similar alterations have been detected in other syndromes (such as irritable bowel syndrome) and this study does not allow us to know whether the diagnosis would be specific to the syndrome studied or simply detect an unhealthy microbiome.