Adipose tissue, broadly classified into white (WAT) and brown adipose tissue (BAT), is an endocrine tissue with a wide-ranging capacity for energy storage and thermogenesis. Within adipocytes, excess energy is stored within large, unilocular lipid droplets (LDs) in WAT or small, multilocular LDs in BAT. While numerous studies have focused on whole-adipose depot characterization, we and others have demonstrated that LDs can be dramatically altered by obesogenic diets, altering both their lipid cargo and biophysical properties. Here, we characterized how diet and exercise progressively reshape LD cargo across WAT and BAT using liquid chromatography-mass spectrometry (LC-MS) based lipidomics. We utilized 8-week-old C57BL/6 male mice that were endurance exercise-trained (4-week voluntary wheel running) or sedentary (static cages) and fed a control (CD; 10% Kcal fat) or high-fat diet (HFD; 45% Kcal fat). First, we contrasted the whole-tissue and LD lipidomes across (four) WAT and BAT and confirmed the biased enrichment of triacylglycerols (TG) in LDs across depots, whereas acylcarnitines (CAR) were enriched in whole tissues. Further, we show that regardless of diet, inguinal WAT (ingWAT) from sedentary mice exhibited progressive increases in LD lipid variance (~220 lipids) across 12 weeks (12- vs. 4-wks; p50 carbons) TG species with variable degrees of unsaturation, indicating widespread lipid remodeling. For iBAT LDs, 4-week training in CD-fed mice reduced and in HFD-fed mice heightened LD cargo variability, compared to diet-matched controls, and HFD-fed trained mice reduced long-chain, unsaturated TG. To demonstrate if the effects of exercise on LD cargo persist once training stops, we profiled LD lipids after 4 weeks of detraining (8wk) followed by 4-week retraining (12wk). Detraining produced similar ingWAT LD lipid variability across all groups, reflecting the catch-up adiposity observed in previously trained groups, although variability remained lower than the training period (8- vs. 4-wks; p< 0.0001). Retraining reversed this pattern: adiposity decreased and ingWAT LD lipid variance increased relative to detraining (12- vs. 8-wks; p< 0.001), though variance did not reach that of diet-matched controls. Only a small number of lipids decreased with retraining, all of which were saturated TG (~50 carbons), pointing to flexible LD lipid packing. Together, findings show that diet and exercise dynamically reshape LD composition across adipose depots, altering lipid packing flexibility that may determine metabolic adaptations and thermogenic function. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
Dabirian et al. (Fri,) studied this question.