Obesity results from a chronic imbalance between energy intake and expenditure, favoring a positive energy balance. Even though physical activity may alter body weight as efficiently as food intake, the mechanisms underlying its control are not well understood. The implications of a sedentary life style extend beyond obesity, and include diabetes mellitus, coronary artery disease, some cancers and premature mortality, so that 1.3 million deaths per year would be prevented by reducing physical inactivity globally in 25%. In this way, it's evident the importance of studies aiming to understand the mechanisms that regulate physical activity. Physical activity is classified in voluntary exercise (sports, gym), and spontaneous physical activity (SPA - body movements to perform routine tasks), which can represent more than 50% of total daily energy expenditure. In this study, our aim is to characterize the acute (the first 48 hours after the beginning of the diet) and chronic (throughout the experiment) SPA of C57bl/6j mice fed a low (6%) protein or a high (34%) fat diet during 12 weeks. As low protein and high fat diet seems to have opposite effects upon SPA, we expect to find also opposite patterns in the expression of genes related to energy homeostasis (PCR Array) and in the insulin and leptin signaling pathway (Western Blot) on hypothalamus. Insulin sensitivity (through the insulin tolerance test) and the plasmatic concentration (ELISA) of insulin, leptin and proinflammatory cytokines (IL-1a, TNF-a) will also be evaluated. Thereby, we expect to identify candidates involved in SPA regulation as well as to characterize the acute and chronic effects of low protein or high fat diet upon SPA.
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