Assessment of Fat Free Mass Index and Its Impact on Health in Children With Cystic Fibrosis
Condition: Cystic Fibrosis
MeSH terms: Cystic Fibrosis; Fibrosis
Study type: Observational

Summary: 
      The purpose of this study is to find out whether measurement of body composition has a
      prognostic value on clinical and overall outcome in pediatric patients with cystic fibrosis.
    

Detailed description: 
      Cystic fibrosis (CF) is one of the most common life-threatening inherited disorders affecting
      1/35000 individuals in the US. In the past decades, the median predicted survival of CF
      patients has increased significantly from 10-12 to over 37 years (1). One of the major
      factors contributing to increased survival has been the understanding of the role of optimal
      nutrition on overall health status of individuals with CF.

      Forced expiratory volume in one second (FEV1) is currently the best predictor of pulmonary
      health in CF, and malnutrition in a person of any age with CF has a negative impact on lung
      function with a more rapid yearly decline in FEV1. Recent data from the Cystic Fibrosis
      Foundation (CFF) patient registries in the United States and Canada were analyzed to
      determine whether any association existed between pulmonary function as measured by FEV1 and
      Body mass index (BMI) for age. BMI-for-age percentile values >50th percentile were associated
      with well-preserved lung function and lower values of BMI were associated with incrementally
      lower values of FEV1 (2). Thus, the CFF recommended that children with CF between the ages of
      2 and 20 years maintain a BMI a≥50th percentile for age and sex. However, several
      publications have demonstrated that fat free muscle (FFM) wasting is evident even in
      individuals with a BMI > 50th percentile, and it is unknown whether BMI percentile adequately
      reflects changes in body composition in this group of patients; therefore, BMI might not be
      the best marker indicating an optimal nutritional status.

      Limitations of BMI as a marker of optimal Nutrition: fat mass versus muscle mass In
      individuals with CF, BMI is used to assess appropriateness of weight to height for age and
      sex. Since there is a strong association between BMI and overall health metrics, especially
      lung health, the CFF recommends that children with CF maintain a BMI ≥50th percentile for age
      and sex. However, an apparent loss of skeletal muscle may occur in CF patients who retain
      their normal body weight, indicating that BMI does not provide any information about body
      compartments and may fail to detect subtle alterations in body composition. Although several
      epidemiologic studies showed that CF patients who maintain BMI> 50th percentile will have
      improved lung functions and survival, recent data indicate that the preserved FFM instead of
      BMI may have an impact on overall survival in CF (7). Because of the variability in the
      levels of both fat mass and fat-free mass, and the many combinations of fat mass index and
      FFM index associated with the same BMI, this weight-height index needs to be carefully
      interpreted. Because high levels of BMI-for-age are associated with substantial increases in
      fat mass, BMI is most useful as a measure of obesity. In chronic inflammatory diseases, a
      change in regional fat distribution is observed with a shift to a more central fat
      distribution. The latter is associated with an increase in low-grade chronic inflammation,
      insulin resistance, and cardiovascular risk (8). Therefore, BMI is a good index for
      assessment of obesity in otherwise normal children, but not adequate or sufficient in the CF
      population.

      In summary, some pediatric patients with CF may have a decreased Fat-free Mass Index (FFMI)
      with a well preserved BMI of ≥50th percentile. Conversely, some patient might have a BMI<50th
      percentile with normal FFMI associated with overall well-being. Current practice forces CF
      patients to consume high fat and caloric nutrients to maintain a BMI >50th percentiles
      incurring the costs of causing anxiety, stress, daily struggle in the family with a potential
      increase in the pro-inflammatory state due to central fat accumulation. The outcome of the
      proposed study will contribute to the understanding of the relationships between BMI, muscle
      wasting and markers of health and wellbeing. If our study demonstrates that a well maintained
      FFMI rather than the BMI correlates better with good health status in CF, it may result in
      changes of current nutrition practice in CF at the national or even international level.
    

Observational model: Cohort
Time perspective: Prospective
Sampling method: Probability Sample
Study population: 
        Children with cystic fibrosis 7-17 years followed at Arkansas Children's hospital Cystic
        Fibrosis Care Center
      
Biospecimen description: 
      Blood sample
    
Keywords: cystic fibrosis; body mass index; fat free mass; Children with cystic fibrosis