Effect of adipose tissue insulin resistance on substrate utilization during low-intensity exercise: a pilot study in...

[Purpose] Impaired insulin-mediated suppression of adipocyte lipolysis, adipose tissue insulin resistance (ATIR), may influence lipolysis and substrate utilization during exercise. This pilot study aimed to investigate the effects of ATIR on metabolic responses and substrate utilization during exercise in young men. [Participants and Methods] Twenty-four young men were divided into two groups based on their ATIR index (Adipo-IR): low Adipo-IR (LA) and high Adipo-IR (HA). The participants performed 40 min of aerobic exercise at an intensity corresponding to 40% peak oxygen uptake. Venous blood samples were collected at baseline and immediately after exercise to measure hormones and metabolite levels. Expired gas was collected during the exercise to estimate substrate oxidation. [Results] After adjusting for whole-body insulin resistance, circulating free fatty acid (FFA) levels at baseline and immediately after exercise were significantly higher in the HA group than in the LA group. The HA group demonstrated significantly lower carbohydrate oxidation and significantly higher fat oxidation than the LA group. Adipo-IR and FFA levels were significantly correlated with parameters of substrate utilization during exercise. [Conclusion] ATIR was associated with substrate utilization during exercise, independent of whole-body insulin resistance. ATIR may play a distinct role in the regulation of substrate utilization during exercise.