Muscle protein loss in chronic kidney disease (CKD) is caused by increased breakdown rather than decreased synthesis. Studies show that factors like inflammation, acidosis, and insulin resistance contribute to this muscle protein degradation. By using isotopically labeled amino acids, researchers can measure the rates of protein synthesis and breakdown in muscle. Results consistently show that CKD patients experience higher muscle protein degradation, leading to muscle wasting. Additionally, changes in the synthesis of myosin heavy chain, a key muscle protein, occur early in CKD.