Assessment of nutritional status in adult patients with cystic fibrosis: whole-body bioimpedance vs body mass index, skinfolds, and leg-to-leg bioimpedance.

OBJECTIVE: To investigate whether body mass index (BMI) or body fat percentage estimated from BMI, skinfolds, or leg-to-leg bioimpedance are good indicators of nutritional status in adult patients with cystic fibrosis. Body fat percentage measured by whole-body bioimpedance was used as the reference method.

DESIGN: Cross-sectional study using four methods to estimate body fat percentage. All patients filled out a food frequency and a physical activity questionnaire for assessment of their habitual food intake and energy requirements, respectively.

SUBJECTS/SETTING: Thirty-five adult patients (23 men/12 women) with cystic fibrosis, age range 18 to 46 years, were measured during their yearly visit at the outpatient clinic of the Cystic Fibrosis Center in Utrecht, the Netherlands.

STATISTICAL ANALYSIS: Mean+/-standard deviation was calculated for all measurements and 95% confidence intervals for differences between methods. Bland-Altman plots were used to assess differences between the measures of body composition and Pearson correlation coefficients were calculated to determine the relationships between them, and between the energy requirements and the energy intakes.

RESULTS: For men the whole-body body fat percentage reference was 14.1%+/-3.0, body fat percentage estimated from BMI was 15.8%+/-4.3, body fat percentage estimated from skinfolds was 8.6%+/-4.8, and body fat percentage estimated from leg-to-leg bioimpedance was 13.1%+/-4.9. For women the whole-body body fat percentage reference was 24.0%+/-5.9, body fat percentage estimated from BMI was 25.1%+/-4.0, body fat percentage estimated from skinfolds was 17.0%+/-4.8, and body fat percentage estimated from leg-to-leg bioimpedance was 25.0%+/-6.9. Body fat percentage estimated from BMI and body fat percentage estimated from skinfolds were significantly different from the reference value for body fat percentage (P <.05). The correlation coefficients between the reference body fat percentage and body fat percentage estimated from BMI, from skinfolds, and from leg-to-leg bioimpedance were all more than 0.72. In all but one patient, nutritional status was correctly assessed by BMI: those with a BMI less than 18.5 had body fat percentage less than 10% (men) or less than 20% (women). The mean energy intake of the men was 141% of the Recommended Dietary Allowance as proposed in European and Dutch guidelines. The mean energy intake of the women was 94% of the Recommended Dietary Allowance.

CONCLUSIONS: A simple calculation of BMI is adequate to diagnose nutritional status in adult patients with cystic fibrosis. Bioimpedance measurements are only needed when nutritional therapy specifically focuses on lean body mass.