Effects of increasing nitrogen intake on nitrogen balance and energy expenditure in nutritionally depleted adult patients receiving parenteral nutrition

The effects of increasing nitrogen intake were studied in 10 nutritionally depleted patients receiving total parenteral nutrition. After 1 to 2 days on 5% dextrose, the patients received, in random order, intravenous diets containing either a low (180 mg/kg·day) or high (364 mg/kg·day) nitrogen content. Equicaloric amounts of glucose and fat emulsion were given. Total energy intake averaged 33.0 kcal/kg·day corresponding to 1.31 × resting energy expenditure or 1.08 × total energy expenditure. Nitrogen and energy balances were measured daily. Concentrations of glucose, glycerol, fatty acids, triglycerides, urea, insulin and glucagon in plasma, and of β -hydroxybutyrate in whole blood were measured during the last 2 days of each diet period. An increase in plasma urea was the only change in hormone or substrate concentrations identified. Resting energy expenditure increased approximately 10%, going from 5% dextrose to the low and from the low to the high N diet. Nitrogen balances were 0.21 and 0.61 mg N/kg·day on the low and high N diets. Nitrogen retention of 21% of the increment in intake, three times that seen in normal adult subjects, indicates that the malnourished patients in this study responded in a manner similar to growing organisms. Attainment of markedly positive N balance at, or close to, zero energy balance indicates that lean body mass can be restored without excessive energy intakes which may often be undesirable.