Responses to dietary macronutrient distribution of overweight rats under restricted feeding

Changes in protein and amino acid balance after energy-restricted feeding have scarcely been studied, although it has been suggested that protein utilization may depend on the macronutrient composition of the restricted diet. The aim of this study is to investigate the influence of dietary fat quality and content, during an energy-restricted regime, on body composition and protein metabolism. Therefore, diet-induced overweight rats were divided into three dietary groups: one group was fed on a control diet ad libitum (control) and the other two groups were fed energy-restricted diets (about 60% of control group), which provided a standard amount (20%) of fat (SFR), based on olive oil, or a high amount (60%) of saturated fat (HFR), based on coconut oil. Measurements of body weight, body composition, serum biochemical parameters and the assessment of the hepatic and muscular protein response were performed. Similar results were found comparing weight losses and serum parameters in both deprived groups, although the high-fat-restricted rats (HFR group) showed a greater reduction in the subcutaneous fat depot and of total body fat. After both energy-restricted treatments, the serum amino acid concentration was reduced while the urinary amino acid excretion increased. Muscle and liver protein metabolism was affected by energy restriction, which produced a decrease in protein synthesis capacity (RNA content) in both tissues and a higher muscle proteolysis (catepsin activity), more marked in the SFR group, while no changes were found in liver protein breakdown. Hepatic glycogen and glycogenic amino acid were also altered, reaching significant differences in the HFR group. Thus, dietary macronutrient composition during energy restriction seems to be involved in the metabolic adaptative response.