At the phylum level, baseline species composition analysis showed that both the MC group and the NC group were dominated by the phyla Bacteroidota and Firmicutes, with the combined relative abundance of these two phyla exceeding 85%, which is consistent with the core composition characteristics of the gut microbiota in patients with stable COPD reported previously. The phylum Firmicutes is involved in intestinal mucosal protection, while the phylum Bacteroidota is involved in protein degradation, polysaccharide degradation, and SCFA production.
In this study, the abundance of Firmicutes showed an increasing trend in the MC group, while the abundance of Bacteroidota showed a decreasing trend. Although these changes did not reach statistical significance, they suggest that there may be an imbalance in the phylum-level microbiota in patients with stable COPD and deficiency syndrome. This imbalance may contribute to immune dysregulation in COPD. An increased ratio of Firmicutes to Bacteroidota (Fir/Bact ratio) is typically associated with obesity, metabolic diseases, and inflammatory states, which may indicate that the microbiota are extracting more energy from food and could also be accompanied by pro-inflammatory changes.