Fig. 7

Metabolomic profiling of faecal samples in normal aging and NCDs groups. A PLS-DA score plot of primary metabolites detected in positive and negative ion modes, indicating a clear separation between the two groups. B PCA of the primary metabolites detected in positive and negative ion modes, confirming the discrimination between the two groups. C Volcano plot of differentially expressed metabolites in positive and negative ion modes between the normal aging and NCDs groups, with blue dots representing downregulated metabolites and red dots representing upregulated metabolites. D Heatmap of significantly differentially expressed metabolites based on adjusted P-values and fold changes. E Variable importance plot from random forest model of significantly differentially expressed metabolites based on VIP values, showing the most influential metabolites for group classification. F Bubble plot of the top 20 significantly enriched KEGG pathways between the normal aging and NCDs groups in negative and positive ion modes, revealing the metabolic pathways that were most affected by NCDs. The metabolites with variable importance in the projection (VIP) > 1 and P < 0.05 and fold change ≥ 2 or FC ≤ 0.5 were differential metabolites. Volcano plots were used to filter metabolites of interest which based on log₂(FoldChange) and − log₁₀(p-value) of metabolites by ggplot2 in R language. When P-value of metabolic pathway < 0.05, metabolic pathway was considered as statistically significant enrichment