Background: Previous studies have demonstrated an increased basal metabolic rate in cancer patients. However, no previous study has investigated the changes in energy expenditure and substrate oxidation after administration of a glucose load. Furthermore, the role of tumor necrosis factor-alpha (TNF-alpha) on cancer-induced metabolic changes is still a neglected area.
Methods: In 25 cancer patients and 16 healthy subjects matched with regard to age, body mass index, and fat-free mass, indirect calorimetry was made before and after administration of a glucose load (75 g per subject, administered orally).
Results: Cancer patients had fasting plasma concentrations of insulin (74 +/- 3.3 vs. 67 +/- 4.1 pmol/L; P < 0.05), lactate (0.68 +/- 0.11 vs. 0.41 +/- 0.1 mmol/L; P < 0.05), free fatty acids (884 +/- 121 vs. 342 +/- 76 mmol/mL; P < 0.001), and TNF-alpha (1.23 +/- 0.31 vs. 0.45 +/- 0.11 ng/mL; P < 0.01) greater than controls, whereas plasma glucose concentrations (4.8 +/- 0.5 vs. 5.1 +/- 0.3 mmol/L; P = not significant) were not different from controls. Indirect calorimetry at baseline demonstrated that basal metabolic rate, fat oxidation, and protein oxidation were significantly greater in cancer patients than in controls. After administration of the glucose load, carbohydrate oxidation progressively rose in both cancer patients and controls, with no differences between the two groups, whereas glucose uptake (59.3 +/- 3.8 vs.69.1 +/- 3.6 g/kg fat-free mass [FFM] x 240 minutes; P < 0.01) and storage (49.1 +/- 4.1 vs. 60.2 +/- 3.3 g/kg FFM x 240 minutes; P < 0.05) were markedly reduced in cancer patients as compared with controls. Finally, glucose-induced thermogenesis (GIT) was lower in cancer patients than in controls.
Conclusions: This study demonstrated that GIT is lower in cancer patients than in healthy subjects matched with regard to age and body mass index. An overactivity of the glucose fatty acid cycle is responsible for such results. Plasma concentrations of TNF-alpha might play a modulating role in the metabolic changes that occur after administration of a glucose load. The role of TNF-alpha on glucose and lipid metabolism in cancer patients would be a worthy subject of future investigations.