Longitudinal trends in nutritional status and the relation between lung function and BMI in cystic fibrosis: a population-based cohort study

Background: A high-calorie diet has been a standard of care in cystic fibrosis (CF) for .3 decades. However, energy requirements may have changed with new treatments and milder genotypes. Objectives: The objectives of this study were to describe longitudinal trends in nutritional status and to evaluate the relation between nutritional status and lung function. Design: This longitudinal cohort study included 909 individuals followed at the Adult CF Clinic in Toronto from 1985 to 2011. Nutritional status was classified on the basis of WHO BMI guidelines. Multivariable linear regression with the use of generalized estimating equations was applied to evaluate the relation between BMI and lung function. Results: The proportion of underweight individuals decreased from 20.6% before 1990 to 11.1% in the most recent decade, whereas the proportion of overweight and obese subjects increased from 7.0% to 18.4% (P , 0.001). Overweight and obese subjects were older, had better lung function, had milder genotypes, and were more often male and pancreatic sufficient. Multivariable regression analyses showed that within the underweight group, an increase in BMI resulted in improved lung function, whereas this effect was half of that in overweight individuals. The greatest advantage of improved nutrition on lung function was observed in the underweight group and in pancreatic insufficient patients. Conclusions: Modification to a high-fat diet may be required in some individuals with CF to optimize nutritional health. Higher BMI is associated with improvements in lung function, although the lung function benefit of increasing one’s BMI (in kg/m 2 )t o .25 is small and needs to be balanced against the known health risks of obesity. Am J Clin Nutr doi: 10.3945/ajcn.112.051409.