29-03: Protein–Energy Malnutrition

GENERAL CONSIDERATIONS

Protein–energy malnutrition occurs as a result of a relative or absolute deficiency of energy and protein. It may be primary, due to inadequate food intake, or secondary, as a result of other illness. For most developing nations, primary protein–energy malnutrition remains among the most significant health problems. It occurs in two distinct syndromes. Kwashiorkor, caused by a deficiency of protein in the presence of adequate energy, is typically seen in weaning infants at the birth of a sibling in areas where foods containing protein are insufficient. Marasmus, caused by combined protein and energy deficiency, is seen where adequate quantities of food are simply not available.

In industrialized societies, protein–energy malnutrition is most often secondary to other diseases. Kwashiorkor-like secondary protein–energy malnutrition occurs primarily in association with hypermetabolic acute illnesses such as trauma, burns, and sepsis. Marasmus-like secondary protein–energy malnutrition typically results from chronic diseases such as chronic obstructive pulmonary disease (COPD), heart failure, cancer, or AIDS. These two syndromes are estimated to be present in at least 20% of hospitalized patients. A substantially greater number of patients have risk factors that could result in them. In both syndromes, protein–energy malnutrition is caused either by decreased intake of energy and protein or by increased nutrient losses related to the underlying illness. For example, diminished energy intake may result from poor dentition or various gastrointestinal disorders. Increased nutrient losses may result from malabsorption, diarrhea, and glycosuria. Increased nutrient requirements occur with fever, surgery, neoplasia, and burns.

PATHOPHYSIOLOGY

Protein–energy malnutrition affects every organ system. The most obvious results are loss of body weight, adipose stores, and skeletal muscle mass. Weight losses of 5–10% are usually tolerated without loss of physiologic function; losses of 35–40% of body weight usually result in death. Loss of protein from skeletal muscle and internal organs is usually proportionate to weight loss. Protein mass is lost from the liver, gastrointestinal tract, kidneys, and heart.

As protein–energy malnutrition progresses, organ dysfunction develops. Hepatic synthesis of serum proteins decreases, and depressed levels of circulating proteins are observed. Cardiac output and contractility are decreased, and the electrocardiogram (ECG) may show decreased voltage and a rightward axis shift. Autopsies of patients who die with severe undernutrition show myofibrillar atrophy and interstitial edema of the heart.

Respiratory function is affected primarily by weakness and atrophy of the muscles of respiration. Vital capacity and tidal volume are depressed, and mucociliary clearance is abnormal. The gastrointestinal tract is affected by mucosal atrophy and loss of villi of the small intestine, resulting in malabsorption. Intestinal disaccharidase deficiency and mild pancreatic insufficiency also occur.