I'd never heard this before; anyone...??
"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)."
Conclusion of the study: "Comparatively small changes in the carbohydrate and fat constitution of meals can have a significant effect on VCO2 [carbon dioxide production], exercise tolerance, and breathlessness in patients with chronic obstructive lung disease."