Increased Protein Turnover Despite Normal Energy Metabolism and Responses to Feeding in Patients with Lung Cancer1

We have examined the responses of energy and protein metabolism to nutrient intake in nine patients with lung carcinoma, of whom none »ere cachexie and only one had distant métastases,compared with nine control patients for elective aneurism surgery, who were comparable in terms of age, body mass index, and smoking habits. Whole-body protein turnover and leucine oxidation were assessed by primed continuous infusion of i |"C|leucine. Indirect calorimetry was used to determine energy expendi ture and rates of carbohydrate and fat utilization. Lean body mass (IHM) was estimated from dilution of deuterium oxide. Measurements were made over an 8-h period, including 4 h postabsorptive followed by 4 h of feeding, during which small hourly meals were consumed. In the postabsorptive state, the rate of incorporation of leucine into protein was higher in the cancer group (mean ±SD, cancer versus control: 102 ±21 versus 86 ±8 /¿mol/kg LBM/h, P < 0.05), as was the release of leucine by protein degradation (126 ±19 versus 110 ±10 Mmol/kg LBM/h, P < 0.01), but there was no difference in rates of leucine oxidation (27 ±6 versus 27 ±5 Mmol/kg LBM/h) or leucine balance (—25±7 versus —¿ 24 ±4 /niKil ky LBM/h). There were no differences between the cancer and control groups with respect to either resting energy expenditure (37.3 ± 3.5 versus 35.2 ±3.8 kcal LBM/day) or the postabsorptive pattern of nutrient utilization (61 ±13% fat, 26 ±10% carbohydrate, and 13 ±2% protein versus 65 ±7%, 21 ±7%, and 14 ±2%, respectively). During feeding, leucine oxidation rose relative to the postabsorptive state, incor poration into protein remained the same, and release by protein degra dation fell. Incorporation (106 ±20 versus 89 ±7 Mmol/kg LBM/h, P < 0.05) and release (59 ±12 venus 42 ±14 Mmol/kg LBM/h, P < 0.02) remained higher in the cancer group than in controls, but leucine oxidation (43 ±15 versus 43 ±12 Mmol/kg LBM/h) and leucine balance (+48 ± 10 versus +47 ±12 Mmol/kg LBM/h) were the same. Energy expenditure during feeding increased to 43.8 ±5.1 versus 43.2 ±4.2 kcal/kg LBM/ day, derived from 32 ±11% fat, 52 ±9% carbohydrate, and 16 ±5% protein in cancer patients and 36 ± 7%, 48 ±8%, and 16 ±4%, respectively, in controls. I luis, newly diagnosed lung cancer patients showed increased protein turnover rates expressed per kg LBM, despite no detectable effect on leucine balance and energy expenditure or on their responses to food intake. Furthermore, these elevated rates of protein turnover were apparent in noncachexic patients and were shown not to depend on the presence of métastases.