Effect of carbohydrate rich versus fat rich loads on gas exchange and walking performance in patients with chronic obstructive lung disease

BACKGROUND: High calorie intakes, especially as carbohydrate, increase carbon dioxide production (VCO2) and may precipitate respiratory failure in patients with severe pulmonary disease. Energy obtained from fat results in less carbon dioxide and thus may permit a reduced level of alveolar ventilation for any given arterial blood carbon dioxide tension (PaCO2). METHODS: Ten patients with stable severe chronic obstructive lung disease underwent a six minute walk before and 45 minutes after taking 920 kcal of a fat rich drink, an isocalorific amount of a carbohydrate rich drink, and an equal volume of a non-calorific control liquid on three separate days, in a double blind randomised crossover study. Borg scores of the perceived effort to breathe were measured at the beginning and end of each six minute walk. Minute ventilation (VE2), VCO2, oxygen consumption (VO2), respiratory quotient (RQ), arterial blood gas tensions, and lung function were measured before and 30 minutes after each test drink. RESULTS: Baseline measurements were similar on all three test days and the non-calorific control drink resulted in no changes in any of the measured variables. The carbohydrate rich drink resulted in significantly greater increases in VE, VCO2, VO2, RQ, PaCO2, and Borg score and a greater fall in the distance walked in six minutes than the fat rich drink (mean fall after carbohydrate rich drink 17 m v 3 m after fat rich drink and the non-calorific control). The increase in VCO2 correlated significantly with the decrease in six minute walking distance and the increase in Borg score after the carbohydrate rich drink. The only significant change after the fat rich drink when compared with the non-calorific control was an increase in VCO2. CONCLUSIONS: Comparatively small changes in the carbohydrate and fat constitution of meals can have a significant effect on VCO2, exercise tolerance, and breathlessness in patients with chronic obstructive lung disease.