Impact of 4 weeks of western diet and aerobic exercise training on whole-body phenotype and skeletal muscle mitochondrial respiration in male and female mice.

High dietary fat intake induces significant whole-body and skeletal muscle adaptations in mice, including increased capacity for fat oxidation and mitochondrial biogenesis. The impact of a diet that is high in fat and simple sugars (i.e., western diet [WD]), particularly on regulation of skeletal muscle mitochondrial function, is less understood. The purpose of the current study was to determine physiologic adaptations in mitochondrial respiratory capacity in skeletal muscle during short-term consumption of WD, including if adaptive responses to WD-feeding are modified by concurrent exercise training or may be sex-specific. Male and female C57BL/6J mice were randomized to consume low-fat diet (LFD) or WD for 4 weeks, with some WD-fed mice also performing concurrent treadmill training (WD + Ex). Group sizes were n = 4-7. Whole-body metabolism was measured using in-cage assessment of food intake and energy expenditure, DXA body composition analysis and insulin tolerance testing. High-resolution respirometry of mitochondria isolated from quadriceps muscle was used to determine skeletal muscle mitochondrial respiratory function. Male mice fed WD gained mass (p < 0.001), due to increased fat mass (p < 0.001), and displayed greater respiratory capacity for both lipid and non-lipid substrates compared with LFD mice (p < 0.05). There was no effect of concurrent treadmill training on maximal respiration (WD + Ex vs. WD). Female mice had non-significant changes in body mass and composition as a function of the interventions, and no differences in skeletal muscle mitochondrial oxidative capacity. These findings indicate 4 weeks of WD feeding can increase skeletal muscle mitochondrial oxidative capacity among male mice; whereas WD, with or without exercise, had minimal impact on mass gain and skeletal muscle respiratory capacity among female mice. The translational relevance is that mitochondrial adaptation to increases in dietary fat intake that model WD may be related to differences in weight gain among male and female mice.