The primary target of nutritional support: body composition or muscle function?

Abstract

In a 70-kg man, skeletal muscle accounts for 40–50% of the total body mass. A loss of the muscle mass due to the net breakdown of muscle proteins is a common feature of many acute and long-term illnesses. During the initial flow phase, patients with an acute critical illness (multiple trauma and sepsis) lose 1–2 kg muscle mass per day and up to half the muscle mass in periods of 1–2 weeks [1]. Many chronic diseases that impair the function of the lungs, liver, kidney and heart including cancer and AIDS (affecting multiple systems) are attended by a generally slower, gradual loss of muscle mass. A very slow, but in the end substantial, loss of muscle mass is also observed during aging (sarcopenia) [2]. The reduction in muscle mass in all these conditions is the major component of the reduction in lean body mass. Impairments are also seen in muscle function, with a reduction in strength and endurance capacity being most evident [2, 3]. This again limits the ability of the patients to walk and perform normal activities of daily living. In some of the chronic diseases, the reduction in muscle function forms a serious disability or even handicap that dramatically reduces their quality of life [3]. This limitation in physical performance and continuous subjective feelings of fatigue are experienced as the most distressing phenomenon of many acquired chronic diseases [3, 4]. In patients with multiple trauma and sepsis, the loss of muscle mass and functions leads to life-threatening complications (e.g. respiratory failure) and is a major cause of death [5]. In clinical nutrition practice, the traditional approach to try and combat excessive rates of muscle protein breakdown is to give the patient more