Obesity is defined by the World Health Organization as an excessive accumulation of fat, such that it becomes a health risk. It is a growing global problem, with 29% of adults in the UK classed as obese in 2017, and is a burden to health services with the NHS reporting that obesity-related illnesses account for more government spending than the police or fire service. It has been linked to changing human behaviour within an obesogenic environment, including more sedentary lifestyles and greater availability of high-fat and high-sugar foods. Most fats are stored in white adipose tissue (WAT), acting as a fuel store which can be mobilized in times of need. WAT is greatly expanded during obesity, whilst changes are observed in tissue morphology and function. The remodelling of WAT during the progression of obesity is, however, incompletely understood. In particular, it is not known whether changes in mitochondrial function are associated with WAT expansion, and whether this affects the balance between lipid synthesis and oxidation. We therefore aimed to investigate mitochondrial respiration in the adipose of C57BL/6J mice fed a high-fat high-sucrose (HFHS) diet or standard laboratory chow for 12 months. Clark-type Oxygen electrodes and a substrate-uncoupler inhibitor assay were used to assess different components of respiration in three types of adipose tissue; inguinal (iWAT) and epididymal (epiWAT) WAT, and intrascapular brown adipose tissue (BAT). Initially, succinate (10 mM) was added to stimulate mitochondrial respiration. This was followed by a titration of the protonophore carbonyl cyanide-4-phenylhydrazone (FCCP; 0.25 µM increments), to uncouple ATP synthase from the electron transfer system. After a peak rate was reached with FCCP additions, antimycin A (10 µM) was added to inhibit complex III and sodium azide (100 mM) added to inhibit complex IV. O2 consumption rates were recorded at baseline and following each addition, whilst the peak rate of O2 consumption following FCCP titration was taken. Rates were corrected to tissue mass. Compared with chow-fed controls, iWAT from HFHS mice had a 57% higher rate of mitochondrial respiration upon activation with succinate (p<0.01), and when FCCP was added O2 consumption was 56% higher in iWAT from HFHS mice (p<0.01). EpiWAT from HFHS-fed mice showed a 35% higher O2 consumption rate in the uncoupled state (p<0.05) compared with controls. BAT from HFHS mice showed 19% lower O2 consumption following antimycin A (p<0.05) compared with controls, whilst in iWAT, complex III-inhibited O2 consumption rate was 42% higher in HFHS mice (p<0.05). This preliminary data highlights that adipose tissue mitochondrial function is altered in diet-induced obesity, with increased respiratory capacity seen in WAT, and non-mitochondrial respiration decreased in BAT but increased in WAT. Lipidomic analysis is ongoing, whilst future work will investigate how alterations in the lipid profile impact on signalling and function of subcellular organelles.