Although maintenance hemodialysis (MHD) patients are often wasted, little is known about their dietary energy needs. We studied four men and two women in a clinical research center while they received diets providing 45, 35 and 25 kcal/kg desirable body weight/day; diets were fed, in random order, for 21 to 23 days each. Protein intake, 1.13 +/- 0.02 (SEM) g protein/kg/day, was similar with all three diets. Body weight rose with 45 and 35 kcal/kg/day (P less than 0.05) and fell with 25 kcal/kg/day (P less than 0.05). Nitrogen balance, adjusted for estimated unmeasured losses, was neutral with 45 and 35 kcal/kg/day and negative with 25 kcal/kg/day. Balance was neutral or positive in 6 of 6, 4 of 6, and 0 of 6 patients fed 45, 35, 25 kcal/kg/day, respectively. Nitrogen balance, many plasma amino acids and changes in body weight, mid-arm circumference, mid-arm muscle area and body fat each correlated with energy intake. Resting energy expenditure was normal. The energy intake estimated from regression equations to maintain neutral nitrogen balance was 38.5 kcal/kg desirable weight/day; for body fat and weight, it was 32 kcal/kg/day. These data suggest that MHD patients have normal energy expenditure and approximately normal requirements for maintenance of protein balance, body weight and body fat. An average energy intake of about 38 kcal/kg desirable weight/day may be necessary to maintain nitrogen balance in these patients.

Although nondialyzed, chronically uremic patients and patients undergoing maintenance hemodialysis often show evidence for wasting and calorie malnutrition and have low dietary energy intakes, their energy expenditure has never been systematically evaluated. It is possible that low energy intakes are an adaptive response to reduced energy needs; alternatively, energy expenditure could be normal or high and the low energy intakes would be inappropriate. Energy expenditure was therefore measured by indirect calorimetry in 12 normal individuals, 10 nondialyzed patients with chronic renal failure, and 16 patients undergoing maintenance hemodialysis. Energy expenditure was measured in the resting state, during quiet sitting, during controlled exercise on an exercise bicycle, and for four hours after ingestion of a test meal. Resting energy expenditure (kcal/min/1.73 m2) in the normal subjects, chronically uremic patients and hemodialysis patients was, respectively, 0.94 +/- 0.24 (SD), 0.91 +/- 0.20, and 0.97 +/- 0.10. There was also no difference among the three groups in energy expenditure during sitting, exercise, or the postprandial state. Within each group, energy expenditure during resting and sitting was directly correlated. During bicycling, energy expenditure was directly correlated with work performed, and the regression equation for this relationship was similar in each of the three groups. These findings suggest that for a given physical activity, energy expenditure in nondialyzed, chronically uremic patients and maintenance hemodialysis patients is not different from normal. The low energy intakes of many of these patients may be inadequate for their needs.

In healthy adult humans, eight amino acids (isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine) were shown classically by nitrogen balance studies to be indispensable. Subsequent studies classifying histidine as indispensable are reviewed in this article. We also review the evidence that in certain nutritional or disease states or in certain stages of development otherwise dispensable amino acids may become indispensable. Arginine, citrulline, ornithine, cysteine, and tyrosine thus may be considered as acquired indispensable amino acids. Evidence for the indispensability of taurine is also considered. We propose a classification of the indispensability of amino acids based on clinical and therapeutic considerations.