Assessment of Fat Free Mass Index and Its Impact on Health in Children With Cystic Fibrosis

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.

Inclusion Criteria:

- Subjects who already have a diagnosis of CF based on universal diagnostic criteria

- Age 7 to 17 years at the time of enrollment

- Under routine medical control at the CF center of Arkansas Children's Hospital(ACH)

- Clinically stable in CF symptoms as determined by investigators

Exclusion Criteria:

- Unstable current diagnosis of metabolic diseases including liver (cirrhosis) or renal
disease

- Failure to give informed consent

- Individuals with pacemakers

- Pregnancy in females of childbearing age. A pregnancy test will be performed on
females who are post-menarche before performing a DEXA scan