On the basis of literature values, the relationship between fat-free mass (FFM), fat mass (FM), and resting energy expenditure [REE (kJ/24 h)] was determined for 213 adults (86 males, 127 females). The objectives were to develop a mathematical model to predict REE based on body composition and to evaluate the contribution of FFM and FM to REE. The following regression equations were derived: 1) REE = 1265 + (93.3 x FFM) (r2 = 0.727, P < 0.001); 2) REE = 1114 + (90.4 x FFM) + (13.2 x FM) (R2 = 0.743, P < 0.001); and 3) REE = (108 x FFM) + (16.9 x FM) (R2 = 0.986, P < 0.001). FM explained only a small part of the variation remaining after FFM was accounted for. The models that include both FFM and FM are useful in examination of the changes in REE that occur with a change in both the FFM and FM. To account for more of the variability in REE, FFM will have to be divided into organ mass and skeletal muscle mass in future analyses.

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The metabolic response to injury and illness as manifested by increases in energy expenditure and nitrogen losses makes it difficult for the clinician to evaluate calorie and protein needs. A method for determining daily calorie needs in hospitalized patients is presented. Average increases in resting metabolic expenditure for a group of patients following elective operation, skeletal trauma, skeletal trauma with head injury, blunt trauma, sepsis and burns were determined by indirect calorimetry and protein need by urinary nitrogen losses over extended time periods. Total daily calorie needs were then calculated, using the Harris-Benedict equation and adjusting this value upward using a previously measured activity and injury factor to arrive at the daily needs. Protein requirements may be determined on periodic 24 hour urine samples analyzed for the urinary urea nitrogen and adjusting this to a total nitrogen or protein equivalent. This approach to estimating the calorie nitrogen needs of the hospitalized patient under various degrees of stress more closely approximates the patient's variable needs at the height of the catabolic response and during convalescence.