53 ASSESSMENT OF NUTRITIONAL STATUS
Harrison’s Manual of Medicine
ASSESSMENT OF NUTRITIONAL STATUS
Stability of body weight requires that energy intake and expenditures are balanced over time. The major categories of energy output are resting energy expenditure (REE) and physical activity; minor sources include the energy cost of metabolizing food (thermic effect of food or specific dynamic action) and shivering thermogenesis. The average energy intake is about 2800 kcal/day for men and about 1800 kcal/d for women, though these estimates vary with body size and activity level. Dietary reference intakes (DRI) and recommended dietary allowances (RDA) have been defined for many nutrients, including 9 essential amino acids, 4 fat-soluble and 10 water-soluble vitamins, several minerals, fatty acids, choline, and water (Table 73-1 and Table 73-2 in HPIM-15). The usual water requirements are 1.0–1.5 mL/kcal energy expenditure in adults, with adjustments for excessive losses. The RDA for protein is 0.6 g/kg body weight. Fat should comprise £ 30% of calories, and saturated fat should be <10% of calories. At least 55% of calories should be derived from carbohydrates.
Malnutrition results from inadequate intake or abnormal gastrointestinal assimilation of dietary calories; excessive energy expenditure; or altered metabolism of energy supplies by an intrinsic disease process.
Both outpatients and inpatients should be considered at risk for malnutrition if they meet one or more of the following criteria:
Unintentional loss of >10% of usual body weight in the preceding 3 months
Body weight <90% of ideal for height (Table 53-1)
Table 53-1 Ideal Weight for Height
Body mass index (BMI: weight/height2 in kg/m2) < 18.5
A body weight <90% of ideal for height represents risk of malnutrition, body weight <85% of ideal constitutes malnutrition, <70% of ideal represents severe malnutrition, and <60% of ideal is usually incompatible with survival. In underdeveloped countries, two forms of severe malnutrition can be seen: marasmus, which refers to generalized starvation with loss of body fat and protein, and kwashiorkor, which refers to selective protein malnutrition with edema and fatty liver. In more developed societies, features of combined protein-calorie malnutrition (PCM) are more commonly seen in the context of a variety of acute and chronic illnesses.
ETIOLOGY The major etiologies of malnutrition are starvation, stress from surgery or severe illness, and mixed mechanisms. Starvation results from decreased dietary intake (from poverty, chronic alcoholism, anorexia nervosa, fad diets, severe depression, neurodegenerative disorders, dementia, or strict vegetarianism; abdominal pain from intestinal ischemia or pancreatitis; or anorexia associated with AIDS, disseminated cancer, or renal failure) or decreased assimilation of the diet (from pancreatic insufficiency; short bowel syndrome; celiac disease; or esophageal, gastric, or intestinal obstruction). Contributors to physical stress include fever, acute trauma, major surgery, burns, acute sepsis, hyperthyroidism, and inflammation as occurs in pancreatitis, collagen vascular diseases, and chronic infectious diseases such as tuberculosis or AIDS opportunistic infections. Mixed mechanisms occur in AIDS, disseminated cancer, COPD, chronic liver disease, Crohn’s disease, ulcerative colitis, and renal failure.
General: weight loss, temporal and proximal muscle wasting, decreased skin-fold thickness
Skin, hair, nails: easily plucked hair, easy bruising, petechiae, and perifollicular hemorrhages (vit. C), “flaky paint” rash of lower extremities (zinc), hyperpigmentation of skin exposed areas (niacin, tryptophan); spooning of nails (iron)
Eyes: conjunctival pallor (anemia), night blindness, dryness and Bitot spots (vit. A), ophthalmoplegia (thiamine)
Mouth and mucous membranes: glossitis and/or cheilosis (riboflavin, niacin, vit. B12, pyridoxine, folate), diminished taste (zinc); inflamed and bleeding gums (vit. C)
Neurologic: disorientation (niacin, phosphorus), confabulation, cerebellar gait, or past pointing (thiamine), peripheral neuropathy (thiamine, pyridoxine, vit. E), lost vibratory and position sense (vit. B12)
Laboratory findings include a low serum albumin, elevated PT, and decreased cell-mediated immunity manifest as anergy to skin testing. Specific vitamin deficiencies may also be present.
For a more detailed discussion, see Dwyer J: Nutritional Requirements and Dietary Assessment, Chap. 73, p. 451; Halsted CH: Malnutrition and Nutritional Assessment, Chap. 74, p. 455 ; and Russell RM: Vitamin and Trace Mineral Deficiency and Excess, Chap. 75, p. 461, in HPIM-15.