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Background: Physical inactivity induces insulin resistance (IR) and metabolic imbalances before any significant changes in adiposity. Recent studies suggest that the beneficial effects of exercise can be potentiated if performed while fasting. This work aimed to compare the subacute effects of fed- and fasted-state single-bout exercise on biochemical parameters and cellular signaling in the metabolism. Methods: The animals were allocated into fed rest (FER), fasting rest (FAR), fed exercise (FEE), and fasting exercise (FAE) groups. The exercise protocol was a 30 min treadmill session at 60% of V˙O 2max . The fasting groups fasted for 8 h before exercise and were killed after 12 h post-exercise. Results: Soleus glycogen concentration increased only in the fasting groups, whereas the triglyceride (TGL) content increased in brown adipose tissue (BAT) and liver in the FAE. The FAE showed decreased plasma total cholesterol concentration compared withthe FAR group. Immunocontent of HSP70, SIRT1, UCP-1, and PGC1-α did not change in any tissue investigated. Conclusions: Our results indicate that physical exercise while fasting can have beneficial metabolic effects on sedentary animals. Remarkably, in the FAE group, there was a reduction in total plasma cholesterol and an increase in the capacity of BAT to metabolize and store nutrients in the form of TGLs.

Introduction and objectives : Obesity represents a major global public health problem. Its etiology is multifactorial and includes poor dietary habits, such as hypercaloric and hyperlipidic diets (HFDs), physical inactivity, and genetic factors. Regular exercise is, per se, a tool for the treatment and prevention of obesity, and recent studies suggest that the beneficial effects of exercise can be potentiated by the fasting state, thus potentially promoting additional effects. Despite the significant number of studies showing results that corroborate such hypothesis, very few have evaluated the effects of fasted-state exercise in overweight/obese populations. Therefore, the aim of this study was to evaluate the subacute effects (12 h after conclusion) of a single moderate-intensity exercise bout, performed in either a fed or an 8 h fasted state, on serum profile, substrate-content and heat shock pathway-related muscle protein immunocontent in obese male rats. Methods : Male Wistar rats received a modified high-fat diet for 12 weeks to induce obesity and insulin resistance. The animals were allocated to four groups: fed rest (FER), fed exercise (FEE), fasted rest (FAR) and fasted exercise (FAE). The exercise protocol was a 30 min session on a treadmill, with an intensity of 60% of VO 2 max. The duration of the fasting period was 8 h prior to the exercise session. After a 12 h recovery, the animals were killed and metabolic parameters of blood, liver, heart, gastrocnemius and soleus muscles were evaluated, as well as SIRT1 and HSP70 immunocontent in the muscles. Results : HFD induced obesity and insulin resistance. Soleus glycogen concentration decreased in the fasted groups and hepatic glycogen decreased in the fed exercise group. The combination of exercise and fasting promoted a decreased concentration of serum total cholesterol and triglycerides. In the heart, combination fasting plus exercise was able to decrease triglycerides to control levels. In the soleus muscle, both fasting and fasting plus exercise were able to decrease triglyceride concentrations. In addition, heat shock protein 70 and sirtuin 1 immunocontent increased after exercise in the gastrocnemius and soleus muscles. Conclusions : An acute bout of moderate intensity aerobic exercise, when realized in fasting, may induce, in obese rats with metabolic dysfunctions, beneficial adaptations to their health, such as better biochemical and molecular adaptations that last for at least 12 h. Considering the fact that overweight/obese populations present an increased risk of cardiovascular events/diseases, significant reductions in such plasma markers of lipid metabolism are an important achievement for these populations.

Although the benefits of exercise can be potentiated by fasting in healthy subjects, few studies evaluated the effects of this intervention on the metabolism of obese subjects. This study investigated the immediate effects of a single moderate-intensity exercise bout performed in fast or fed states on the metabolism of gastrocnemius and soleus of lean and obese rats. Male rats received a high-fat diet (HFD) for twelve weeks to induce obesity or were fed standard diet (SD). After this period, the animals were subdivided in groups: fed and rest (FER), fed and exercise (30 min treadmill, FEE), 8 h fasted and rest (FAR) and fasted and exercise (FAE). Muscle samples were used to investigate the oxidative capacity and gene expression of AMPK, PGC1α, SIRT1, HSF1 and HSP70. In relation to lean animals, obese animals' gastrocnemius glycogen decreased 60 %, triglycerides increased 31 %; glucose and alanine oxidation decreased 26 % and 38 %, respectively; in soleus, triglycerides reduced 46 % and glucose oxidation decreased 37 %. Exercise and fasting induced different effects in glycolytic and oxidative muscles of obese rats. In soleus, fasting exercise spared glycogen and increased palmitate oxidation, while in gastrocnemius, glucose oxidation increased. In obese animals' gastrocnemius , AMPK expression decreased 29 % and SIRT1 increased 28 % in relation to lean. The AMPK response was more sensitive to exercise and fasting in lean than obese rats. Exercise and fasting induced different effects on the metabolism of glycolytic and oxidative muscles of obese rats that can promote health benefits in these animals. [Display omitted] • Exercise and fasting induced different effects in glycolytic and oxidative muscles of obese rats. • In oxidative muscles, fasting and exercise spared glycogen and increased palmitate oxidation. • Fasting and exercise increased glucose oxidation in glycolytic muscles of obese animals. • AMPK response is more sensitive to exercise and fasting in lean than obese rats. • AMPK response is different between oxidative and glycolytic muscles. [ABSTRACT FROM AUTHOR]