Retatrutide is an triple agonist of GLP-1, GIP, and glucagon receptors that may promote substantial weight loss, making muscle preservation important. Adequate protein supports muscle protein synthesis, while progressive resistance training signals the body to retain lean tissue. Carbohydrates also provide glucose for glycogen replenishment, training performance, and ATP production, particularly during intense exercise. Total energy intake, food quality, activity, and metabolic responses determine thermogenesis.