Body Mass Index and Clinical Outcomes in Persons Living With Cystic Fibrosis—Is Bigger Always Better?

Cystic fibrosis (CF) is the most common lethal genetic disorder in the White population, affecting nearly 100 000 individuals worldwide.1 Variations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene leads to abnormal chloride and bicarbonate ion transport, propagating the hallmark of disease sequelae including impaired mucus hydration, abnormal clearance, and multiorgan involvement.2 Malnutrition has been frequently associated with CF by several mechanisms, including chronic airway infections, pancreatic insufficiency, and CF-related diabetes (CFRD).3 Furthermore, increased energy expenditure from chronic inflammation and advanced lung disease over time accentuates the trajectory of progression.Underweight status has been independently associated with adverse clinical outcomes in CF, including worsening lung function, morbidity, and mortality.3 Not surprisingly, CF management guidelines have focused primarily on attenuation of nutritional failure with recommendations to maintain a body mass index (BMI) above 22 (calculated as weight in kilograms divided by height in meters squared) in women and 23 in men. 4 While advanced efforts to promote adequate nutrition, including the use of pancreatic enzyme replacement therapy, CFTR modulators, and high caloric diets have reduced malnutrition in this population, over the past decade an increase of patients with CF who are overweight has emerged.Notably, a cross-sectional database analysis of 484 adults with CF found 25% of those with severe variations were overweight or obese.5 As the prevalence of obesity and overweight status becomes a greater concern, the emphasis on high-fat and high-carbohydrate diets for patients with CF is brought into question.Nagy et al 6 examined the association between BMI and clinical outcomes in CF through a large meta-analysis and systematic review.The group evaluated cohort studies, case series, and clinical trials that included patients with CF aged 2 years or older with altered body composition.While BMI is accepted as a marker of nutritional status, its flaws include the inability to distinguish between major components of body composition.Thus, the authors defined abnormal markers as elevated BMI, fat mass, and/or free-fat mass regardless of sex, the presence of transplant, CFTR modulator therapy, or other comorbidities.Given the limited studies available, the authors focused primarily on comparing patients of different BMI ranges as delineated by the World Health Organization by underweight (BMI<18.5),normal weight (BMI 18.5-24.9),overweight (BMI 25-29.9),and obese (Ն30).Primary outcomes of interested included forced expiratory volume in the first second of expiration (FEV 1 ) as a surrogate for lung function, presence of exocrine pancreatic insufficiency, and/or CFRD.Using both a qualitative (9114 patients and 61 records) and quantitative (3100 patients and 17 records) approach, the authors were able to analyze large cohorts of the population of interest.6 Notably, the mean (SD) BMI ranged from normal (18.5 [1.7]) to obese (34.8 [5.7) with 30% of the population evaluated including children.Most studies included FEV 1 as a marker of lung function with patients who were overweight or obese having superior lung function compared with those in the normal BMI category (82.96% vs 72.60%; weighted mean difference (WMD), -8.36%; 95% CI, -12.74% to -3.97% vs WMD, -12.06%; 95% CI, -23.91% to -0.22% respectively).Conversely, patients with underweight nutritional status had significantly lower FEV 1 across all age ranges (WMD, -19.12%; 95% CI, -23.53% to -14.71%).With regards to pancreatic function status, normal BMI was associated with a higher likelihood of exocrine pancreatic insufficiency compared +

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