The Effect of High Protein-High Fat and High Protein-High Carbohydrate Meals on Resting Metabolic Rate and Metabolic Factors in Overweight and Obese Adults: The Study Protocol for a Randomized Crossover Clinical Trial.

Background: The macronutrient composition of daily meals plays a crucial role in influencing the body's metabolic responses during the postprandial phase. However, existing research on the effects of macronutrients, particularly fats and carbohydrates, has produced inconsistent findings.

Objectives: This study aims to evaluate the postprandial effects of two high-protein meals-one low in fat and high in carbohydrates (HP-LF-HC) and the other high in fat and low in carbohydrates (HP-HF-LC)-on energy metabolism, appetite response, and blood markers in overweight and obese men and women without underlying health conditions.

Methods: This study was conducted as an acute randomized crossover clinical trial at the Health Monitoring Center of Mashhad University of Medical Sciences (MUMS) within Imam Reza Hospital, Mashhad, Iran. A total of 30 overweight and obese men and women, meeting the eligibility criteria and free of underlying diseases, were recruited through a public call. Participants were randomly assigned to receive both intervention meals, with a washout period of at least one week between each trial.

Results: The primary outcomes focused on the acute effects of the two dietary interventions on energy metabolism, particularly resting metabolic rate (RMR), and appetite response. Secondary outcomes included changes in lipid profiles, insulin, blood glucose levels, thyroid hormones, and epinephrine.

Conclusions: This study aims to identify which macronutrient composition most effectively enhances resting energy expenditure. The findings could provide valuable insights for dietitians in developing more efficient dietary plans, helping overweight and obese individuals maintain an ideal weight or achieve weight loss by modifying food composition without altering meal volume.