Protein-Energy Undernutrition
(Malnutrition)
A deficiency syndrome caused by inadequate intake or absorption of macronutrients.
Marasmus and kwashiorkor are two forms of protein-energy undernutrition. Marasmus is a condition of borderline nutritional compensation in which a patient has a marked depletion of muscle mass and fat stores but normal visceral protein and organ function. Because the patient has depleted nutritional reserves, any additional metabolic stress (eg, surgery, infection, burn) may rapidly lead to kwashiorkor (hypoalbuminemic protein-energy malnutrition). Kwashiorkor is characterized by a loss of visceral protein and is often associated with edema.
About 16% of elderly persons living in the community consume < 1000 kcal/day, an amount that does not maintain adequate nutrition. Undernutrition also affects 17 to 65% of those in acute care hospitals and 5 to 59% of those in long-term care institutions. Protein-energy undernutrition can lead to many acute and chronic conditions (see Table 61-1). Studies show that elderly persons who are underweight in middle age and later are at greater risk of death than those who are overweight.
Failure to thrive, a term borrowed from the pediatric literature to describe children with delayed physical growth, is applied to the elderly to indicate a deterioration in functional status disproportional to their disease burden. The causes of failure to thrive are multifactorial and include protein-energy undernutrition, loss of muscle mass (sarcopenia), problems with balance and endurance, declining cognition, and depression.
Pathophysiology
The physiologic changes of aging place elderly persons at risk of undernutrition. For example, a physiologic decline in food intake occurs. The reasons for this decline are not known, but several factors may be involved.
Elderly persons appear to feel fuller with less food, which may be caused by a decrease in the opioid (dynorphin) feeding drive and an increase in the satiety effect of cholecystokinin. Recent studies suggest that early satiety in the elderly may be caused by a nitric oxide deficiency, which decreases the adaptive relaxation of the fundus of the stomach in response to food.
Leptin, a recently discovered protein hormone produced by fat cells, decreases food intake and increases energy metabolism. In normal younger adults, an increase in body fat triggers an increase in leptin levels, and vice versa. In contrast, abnormally elevated leptin levels are strongly correlated with decreased body fat, and leptin deficiency in children has been reported to result in massive obesity. In elderly women, leptin levels decline with the decline in body fat that occurs after age 70. In elderly men, however, leptin levels increase despite the decline in body fat. This increase is related to the decline in testosterone levels that occurs with age. The importance of leptin in decreasing food intake with age is unknown. Postmenopausal women with high leptin levels tend to eat somewhat less than those with low leptin levels.
A number of cytokines (eg, tumor necrosis factor, interleukin-2, interleukin-6) decrease food intake. Some elderly persons have elevated levels of these cytokines, which may contribute to anorexia. Stressors (eg, surgery, infection, burns) usually result in cytokine release, which inhibits the production of albumin and causes it to move from the blood into the extravascular space. This occurrence explains the often dramatic decrease in albumin (which has a relatively long half-life of 21 days) of newly hospitalized patients. Characteristically, elderly patients experience this reduction more rapidly than younger patients; even relatively minor stress may be the cause. Usually, susceptible elderly patients are underweight, but even those who appear to have ample fat and muscle mass are susceptible if they have a recent history of rapid weight loss.
Activin, a hormone produced by the testes and ovaries, has been associated with the wasting syndrome in transgenic mice. With age, activin levels increase in men, but not in women; this finding may explain the greater decrease in food intake seen in men compared with women.
Etiology
Except in a hypermetabolic or malabsorption state (eg, hyperthyroidism), malnutrition is generally caused by anorexia. Anorexia has been related to the physiologic changes that occur with age and with various pathologic conditions (see Table 61-2).
A diminished sense of smell and taste may decrease the pleasure of eating, but changes in taste appear to play a minor role in decreased food intake, even though many elderly persons complain that food does not taste as good as it used to. Changes in taste are variable and are often associated with lifelong cigarette smoking, poor dental hygiene, and disease.
Dysphagia due to a stroke, another neurologic disorder, or esophageal pain caused by candidiasis may lower food intake, as may dental problems and xerostomia.
Tremors and other physical problems that make eating difficult (eg, an inability to cut food after a stroke) can also be causative. Continuous tremors from such conditions as Parkinson's disease may cause weight loss by markedly raising the metabolic rate.
The use of certain drugs can result in weight loss by causing anorexia (eg, digoxin, fluoxetine, quinidine, hydralazine, vitamin A, psychoactive drugs); by causing nausea (eg, antibiotics, theophylline, aspirin); by increasing energy metabolism (eg, thyroxine, theophylline); or by causing malabsorption (eg, the sorbitol vehicle in theophylline elixir, cholestyramine). Also, withdrawal from certain drugs (eg, from alcohol, anxiolytics, or psychoactives) may cause weight loss. Alcoholism in late life is often associated with weight loss, squalor syndrome (living in unhygienic conditions), and depression.
Depression is one of the most common reversible causes of weight loss in the elderly. Depressed elderly persons are more likely to lose weight than depressed younger persons. Some very old persons may stop eating because they have lost the joy of living but are not clinically depressed. Loneliness can diminish the desire to prepare meals.
Poverty can also cause low food intake. Problems with shopping and food preparation may result in insufficient food being available in the home.
Anorexia nervosa may recur in elderly persons who had an episode in their teens; this disorder is being increasingly recognized. Abnormal attitudes about food intake and body image are not rare among the underweight elderly. When these abnormal attitudes are associated with severe weight loss, the condition is called anorexia tardive.
Paranoia and mania may have a late-life onset and are also associated with weight loss.
Dementia usually results in weight loss because the person forgets to eat. In addition, persons who wander can use up large amounts of calories in a single day, but persons with Alzheimer's disease do not have increased metabolism. Persons with dementia may have pica, including coprophagy (the ingestion of feces). In advanced dementia, self-feeding and even assisted feeding may become impossible.
Other medical causes of weight loss include hyperthyroidism, Addison's disease, hypercalcemia, pheochromocytoma, cancer, and chronic infections (eg, tuberculosis, recurrent Clostridium difficile diarrhea). In some elderly persons, Helicobacter pylori infections have been associated with severe anorexia and weight loss. Malabsorption syndromes, particularly late onset of celiac disease and pancreatic insufficiency, should also be considered. Cholelithiasis can result in early satiation and weight loss.
Screening and Diagnosis
 The Mini Nutritional Assessment is the best validated nutritional screening device for elderly persons (see Figure 61-1) and has been translated into numerous languages. The SCALES screening device has been cross-validated with the Mini Nutritional Assessment; it is easy to use in the outpatient setting (see Table 61-3). The Specific Global Assessment of nutritional status has been validated for use in hospitalized patients with gastrointestinal disorders but requires further validation for determining malnutrition among elderly persons. The Nutrition Screening Index was developed to identify elderly persons at risk of nutritional problems but has poor specificity and sensitivity.
Weight loss is the single best factor for predicting persons at risk of malnutrition. Adequate height and weight tables for optimum body mass for the elderly are not available, but a body mass index < 21 kg/m2 (weight/height2) suggests a problem. Midarm circumference or midarm muscle circumference (which corrects for triceps skinfold thickness by allowing for subtraction of fat mass) can help detect muscle mass changes in persons retaining fluid. Skinfold thickness measurements have little diagnostic value.
Albumin is an excellent measure of protein status. Healthy ambulatory elderly persons have serum albumin levels > 4 g/dL (3.5 g/dL because of fluid shifts when recumbent). Albumin levels < 3.2 g/dL in hospitalized elderly persons are highly predictive of subsequent mortality. Measurement of short-lived proteins (eg, prealbumin, retinol binding protein) has little diagnostic value but, in certain situations (eg, in intensive care units), may help evaluate the response to therapy.
Cholesterol levels < 160 mg/dL (< 4.15 mmol/L) in nursing home residents predict mortality, presumably because such levels reflect malnutrition. Acute illness associated with cytokine release can also lower cholesterol levels.
Anergy (failure to respond to common antigens, such as mumps, injected into the skin) can occur in healthy as well as in malnourished elderly persons. The combination of anergy and signs of malnutrition correlates more strongly with a poor outcome than does either one alone.
In persons with marasmus, edema is absent; serum albumin and hemoglobin levels, total iron-binding capacity, and test results of cell-mediated immune function (to detect anergy) are usually normal. In persons with kwashiorkor, anergy and edema are often present. The serum albumin level is < 3.5 g/dL, and anemia, lymphocytopenia, and hypotransferrinemia (evidenced by a total iron-binding capacity < 250 µg/dL [< 45 µmol/L]) are likely.
Treatment
Overall, undernutrition is poorly recognized and treated in elderly persons. Thorough examination for treatable causes of weight loss is essential. Appropriate use of short-term aggressive caloric supplementation can save lives (ethical concerns regarding the appropriate withdrawal of nutritional support are discussed elsewhere).
Two recent studies have suggested that at least half of elderly persons in hospitals receive insufficient calories to meet their basic needs. These patients have much worse outcomes than those who receive adequate calories. Also, recent studies show that elderly persons with hip fractures benefit from oral caloric supplements or, if their albumin level is < 3 g/dL, from short-term tube feeding. Total parenteral nutrition should be reserved for severely undernourished persons (those with an albumin level < 3 g/dL) and for those who cannot tolerate enteral feedings. Peripheral vein parenteral nutrition (see Table 61-4) appears to be underused in acutely ill elderly persons, in part because it has been poorly studied.
There are little data to guide the choice of nutrient supplements. High-protein supplements are generally used for persons with infections. High-fat, high-fiber diets may lessen the glycemic response in persons with diabetes. High-fiber diets may reduce tube feeding-induced diarrhea but may result in fecal impaction in immobile patients. In most cases, the choice of a supplement should be based on the patient's preference. For tube feeding, the most cost-effective supplement should be used.
Adverse effects (eg, electrolyte abnormalities, hyperglycemia, aspiration pneumonia) may result from the feeding of a malnourished elderly person. Food can cause a significant drop in blood pressure, which is associated with falls and syncope. The decrease in blood pressure results from carbohydrate, which releases the vasodilatory calcitonin gene-related peptide.
For long-term tube feedings, most patients prefer percutaneous enteral gastrostomy tubes to nasogastric tubes. Patients with dementia tend to pull out gastrostomy tubes less often than nasogastric tubes. All types of tube feedings carry the risk of aspiration. Recent studies have shown that long-term tube feeding is associated with multiple complications and that in many cases outcomes are no better than when tube feeding is not used. This finding suggests the need for more careful targeting of elderly persons who will benefit from tube feeding.
Recombinant growth hormone has been used to retain nitrogen and increase weight in severely malnourished elderly persons. Some of the newer growth hormone secretagogues may be ideal for this purpose. Use of medroxyprogesterone has led to weight gain in elderly persons with lung cancer and in nursing home residents (in one study). Use of dronabinol has led to weight gain in nursing home residents with dementia (in one study). Use of oxoglutarate (not available in the USA) has had dramatic effects on weight gain in elderly persons in Europe.
For patients with tremors or other physical problems with eating (eg, an inability to cut food after a stroke), using adaptive utensils, such as a heavy-handled spoon or a rocker-bottom knife, can help.
Nursing Issues
Food intake of nursing home residents is often underestimated. Nurses need training in appropriate estimation of the amount of food eaten. A number of simple procedures can improve the food intake of nursing home residents (see Table 61-5). |
