Clinical nutrition: 1. Protein-energy malnutrition in the inpatient

This patient is suffering from protein-energy malnutrition (PEM), a pathologic depletion of the body's lean tissues caused by starvation, or a combination of starvation and catabolic stress. In this case, the diagnosis is evident from the physical examination, which reveals a combination of generalized fat and muscle loss typical of the disease, and from the history of prolonged grossly inadequate food intake. PEM is easiest to diagnose when fat stores are depleted, but it can occur without apparent fat loss in previously obese patients, in chronic protein deficiency without energy deficiency, and in highly protein-catabolic states. The lean tissues are the fat-free, metabolically active tissues of the body, namely, the skeletal muscles, viscera, and the cells of the blood and immune system. They account for 35%-50% of the total weight of a healthy young adult, with fat (20%-30%), extracellular fluid (20%), and the skeleton and connective tissue (10%-15%) accounting for the rest. Because the lean tissues are the largest body compartment, their rate of loss is the main determinant of total weight loss in most cases of PEM, and it is for this reason that serial body weight measurements are so useful for assessing the tempo and severity of the disease. A weight loss of 40%-50% is usually incompatible with survival, at least in older adults, whereas milder lean tissue depletions induce important biochemical and functional abnormalities. These abnormalities, together with immune system dysfunction, are evident after involuntary weight loss exceeds about 10% and become highly physiologically obtrusive when weight loss exceeds about 15%. PEM is characterized by atrophy and weakness of the skeletal muscles (including the respiratory muscles), reduced heart muscle mass, impaired wound healing, skin thinning with a predisposition to decubitus ulcers, immune deficiency, fatigue, apathy and hypothermia (Fig. 1).1-9 The extracellular fluid compartment typically expands in PEM, occasionally causing edema. Although lean tissue loss of more than 40% signals imminent death, patients with lesser, but significant, lean tissue loss are at increased risk from their primary disease, its complications and other coincident diseases. PEM is caused by starvation. It is the disease that develops when protein intake or energy intake, or both, chronically fail to meet the body's requirements for these nutrients.16 PEM has always been a common disease, and humans have adaptive mechanis