Energy and respiratory metabolism in cystic fibrosis: the influence of carbohydrate content of nutritional supplements

The basal energy expenditure (BEE) in a group of adolescent and young adult patients with cystic fibrosis (CF) with mild lung disease was 97 +/- 6% of that predicted by the Harris-Benedict equation (which estimates BEE by age, sex, height, and weight). The BEE of a group with more severe lung disease was 117 +/- 5% of that predicted by the Harris-Benedict equation, due primarily to a 14% greater oxygen consumption (Vo2) and 24% greater CO2 production (Vco2) compared with milder lung disease (p < 0.05). The measured BEE in the patients with mild lung disease correlated well with the predicted BEE, but variably underestimated that of patients with more advanced lung disease. The influence of low carbohydrate (Pulmocare) and higher carbohydrate (Instant Breakfast) nutritional supplements on the energy and pulmonary metabolism was compared in 10 malnourished CF patients with moderate to severe lung disease. Their BEE before ingesting the supplements was 120% of that predicted by the Harris-Benedict equation. Their Vco2 increased 9-19% for the 3 h after ingesting 500 kcal/M2 of Pulmocare, and 25-30% after ingesting Instant Breakfast (p < 0.05). The respiratory quotient (RQ) was significantly greater for Instant Breakfast than Pulmocare. The minute ventilation (VE) rose 10-13% for the 3 h after ingesting Pulmocare, versus 27-31% after ingesting Instant Breakfast, but the difference was not significant. The metabolic expenditure rose 13-16% for the 3 h after ingesting both formulas. We concluded that CF patients have increasing difficulty maintaining their nutrition as their pulmonary disease progresses, in part because of a 17-20% increase in their BEE. Pulmocare resulted in a lower Vco2 and RQ than Instant Breakfast, suggesting it is a reasonable nutritional supplement in CF patients with moderate to severe pulmonary disease.