Updated project metadata. Background: Despite recent studies investigating the involvement of single cells in regional differences of the small intestine (SI), the metabolic contribution of the duodenum, jejunum, and ileum to the overall intestinal metabolism is still unclear. Basic procedures and main findings: Using an untargeted proteomics approach, we identified similarities and differences between the three intestinal tracts of C57BL/6J mice and found that proteins highly abundant in the mouse ileum correlated with high ileal expression of the corresponding genes in humans. Consistent with human data, we detected increasing abundance of lysosomal acid lipase (LAL) in C57BL/6J mice from the duodenum to ileum. LAL is the only enzyme known to degrade triacylglycerols and cholesteryl esters within the lysosome. Lipid accumulation in various organs along with gastrointestinal disturbances and malabsorption are typical features of patients and mice with LAL deficiency. We previously demonstrated that macrophages massively infiltrate the SI of Lal-deficient (KO) mice, especially the duodenum. To identify potential mechanisms behind the intestinal lipid accumulation and infiltration of immune cells, we used untargeted proteomics. Our results revealed a general inflammatory response and a common lipid-associated macrophage phenotype in all three intestinal segments of Lal KO mice, accompanied by higher expression of GPNMB and increased concentrations of circulating sTREM2. However, only duodenal macrophages activated a metabolic switch from lipids to other pathways such as glycolysis, TCA cycle, and oxidative phosphorylation to meet their high energy demand. Unexpectedly, these pathways were downregulated in the jejunum and ileum of Lal KO mice. Conclusion: Our results provide new insights into the process of absorption in control mice and the basis for novel markers of LAL-D and/or systemic inflammation in LAL-D.