**Figure 3.** **Fed-state serum metabolome and enriched pathways impacted by aging.** Serum samples from 3-, 12-, 18- and 28 months old (3M, 12M, 18M and 28M) mice at the fed state were analyzed (n=4, 5, 4 and 4, respectively). (**A**) PCA analysis shows the grouped discriminations of the different age groups. 12M and 18M groups clustered together on the PC1 axis. (**B**) Mummichog pathway analysis plot, using peaks-to-pathway analysis module in MetaboAnalyst 4.0. The color and size of each circle corresponds to its p-value and enrichment factor, respectively. The enrichment factor of a pathway is calculated as the ratio between the number of significant pathway hits and the expected number of compound hits within the pathway [69]. The corresponding pathways are listed in Table 1.