Obesity drives systemic metabolic dysfunction, yet how the body adapts and recovers at a system-wide level remains unclear. Here we generate a multi-tissue proteomic atlas of diet-induced obesity and its regression in mice. Using a standardized, semi-automated sample preparation workflow, we quantify 12,936 unique proteins across 15 organs and 4 timepoints. We found proteomic changes to be highly tissue-dependent with a small number of proteins displaying shared changes across multiple tissues. While proteomes of most tissues revert to lean levels after weight loss, white adipose tissue retains strong phagocytic and inflammatory responses, and brain, kidney, bone, thymus, and spleen display delayed obesity-induced alterations. We map the adipose tissue-specific immune regulators using ligand-target inference and show reduced expression of proteasomal subunits in brown adipose tissue, resulting in stalled ubiquitin turnover. Finally, we make all datasets open access and create an interactive Reactome-based webtool to facilitate further community-driven discovery.