VO2peak is a key health benefit of aerobic exercise
however, chronic hyperglycemia is associated with persistently low VO2peak due to an impaired adaptive response to training. Here, we tested whether reducing blood glucose with a low-carbohydrate/high-fat "ketogenic" diet could restore aerobic exercise adaptation in a mouse model of hyperglycemia. Hyperglycemia was induced by streptozotocin (STZ) and mice were stratified to standard chow (STZ-CHOW), or a ketogenic diet (STZ-KETO), which rapidly normalized blood glucose. After aerobic exercise training, improvements in VO2peak were blunted in STZ-CHOW, but exercise response was restored in STZ-KETO. Improved VO2peak in STZ-KETO was associated with enhanced aerobic remodeling of skeletal muscle, including a more oxidative fiber-type and increased capillary density, along with restoration of circulating angiogenic markers. Moreover, KETO induced exercise-independent effects on muscle mitochondrial remodeling and mitochondrial dynamics, significantly increasing fatty acid oxidation. Our results identify a ketogenic diet as a potential therapy to improve aerobic exercise response in the growing population with hyperglycemia due to diabetes and other metabolic conditions.