Visceral lipid accumulation, organ hypertrophy and a reduction in skeletal muscle strength are all signs associated with the severity of obesity-related disease. Intermittent fasting (IF) and high-intensity intermittent exercise (HIIE) are natural strategies that, individually, can prevent and help treat obesity along with metabolic syndrome and its associated diseases. However, the combinatorial effect of IF and HIIE on energetic metabolism is currently not well understood. We hypothesized that their combination could have a potential for more than strictly additive benefits. Here, we show that two months of every-other-day intermittent fasting regimen combined with a high-intensity intermittent exercise protocol (IF/HIIE) produced a synergistic effect, enhancing physical endurance (vs. control, HIIE and IF) and optimizing metabolic pathways of energy production in male Wistar rats. The IF/HIIE group presented enhanced glucose tolerance (vs. control, HIIE and IF), lower levels of plasma insulin (vs. control and HIIE), and a global activation of low Km hexokinases in liver (vs. control, HIIE and IF), heart (vs. control and HIIE) and skeletal muscle (vs. control, HIIE and IF). The IF/HIIE synergism, rather than a simply additive effect, is evidenced by increase in muscle mass and cross-section area, activation of the FoF1 ATP synthase, and the gain of characteristics suggestive of augmented mitochondrial mass and efficiency observed in this group. Finally, important reductions in plasma oxidative stress markers were present preferentially in IF/HIIE group. These findings provide new insights for the implementation of non-pharmaceutical strategies to prevent/treat metabolic syndrome and associated diseases.

2Visceral lipid accumulation, organ hypertrophy and a reduction in skeletal muscle 3 strength are all signs associated with the severity of obesity related disease. Intermittent 4 fasting (IF) and high-intensity intermittent exercise (HIIE) are natural strategies that, 5 individually, can prevent and ameliorate obesity along with metabolic syndrome and its 6 associated diseases. However, the combinatorial effect of IF and HIIF on energetic 7 metabolism is currently not well understood. We hypothesized that their combination 8 could have a potential for more than strictly additive benefits. Here, we show that two 9 months of every-other-day intermittent fasting regimen combined with a high-intensity 10 intermittent exercise protocol (IF/HIIE) produce a synergetic effect, preventing fat 11 accumulation, enhancing physical performance and optimizing energy production. The 12 IF/HIIE group presented increased glucose uptake, lower levels of serum insulin and a 13 global activation of hexokinases in skeletal muscle, heart and liver comparing to control, 14 IF and HIIE groups. IF/HIIE synergism led to activation of the FoF1 ATP synthase and 15 promoted a more oxidative profile of mitochondria in observed skeletal muscle. 16 Additionally, high-resolution respirometry of muscle fibers showed that animals in the 17 IF/HIIE group presented characteristics suggestive of augmented mitochondrial mass 18 and efficiency. Finally, an important reduction in serum oxidative stress markers were 19 observed in IF/HIIE group. These findings provide new insights for the implementation 20 of non-pharmaceutical strategies to prevent/treat metabolic syndrome and associated 21 diseases. 22 1 Introduction 2Obesity and metabolic syndrome are both important risk factors for life threatening 3 diseases that can target cardiovascular and hepatic systems (1, 2). The prevalence of obesity 4 and metabolic syndrome is a reality for developed countries, which began more than two 5 decades ago (3). Today, the incidence of obesity and metabolic syndrome is rapidly 6 increasing in developing countries as well (4), leading to increased morbidity and mortality 7 due to type 2 diabetes mellitus, non-alcoholic fatty liver disease, and cardiovascular disease 8 (5, 6). Recently, global climate change was implicated in the onset of obesity and type 2 9 diabetes due to the negative impact of higher temperatures on energy metabolism (7, 8).10 This means that the overall prevalence of obesity and metabolic syndrome tends to 11 aggravate in the next few years allied with the increased reduction in physical activity (9). 12Intermittent fasting (IF) regimens and high-intensity intermittent exercise (HIIE) are 13 two natural strategies to prevent and mitigate obesity related diseases (10, 11). An every-14 other-day IF regimen was recently demonstrated by Li, Xie (12) to dramatically reduce 15 obesity, insulin resistance, and hepatic steatosis in rodents by altering the gut microbiota. 16 Conversely, the adaptations promoted by HIIE in rodents has been demonstrated ...