Markers for the Validation of Reported Dietary Intake in Adults with Cystic Fibrosis

Abstract Objective To identify different markers in order to validate the assessment of dietary intake in adults with cystic fibrosis (CF). Design Cross-sectional survey. Setting Tertiary care. Subjects We assessed 37 adults with CF whose nutritional and respiratory condition was stable and 37 healthy adults, matched for age, sex, and nutritional status. Interventions A consecutive, 7-day, prospective dietary survey was given to all the participants. Anthropometric variables were measured and a fasting blood sample was drawn to measure the composition of the serum phospholipid fatty acids by gas chromatography. We also measured fecal fat and nitrogen at 72 hours and 24-hour urine nitrogen. Results The ratio of energy intake to basal metabolic rate expenditure was significantly greater in the patients (2.1±0.4) than the controls (1.79±0.4) and the percentage of patients with the ratio of energy intake to basal metabolic rate lower than 1.55 was 24% in the controls (n=9) vs 8% in the patients (n=3). Fecal nitrogen correlated significantly with total energy and the intake of carbohydrates, lipids, and proteins. In the patients, total dietary energy and fat and protein intake correlated positively with fecal fat. The protein and fat intake and fecal nitrogen and fat correlated significantly with urine nitrogen. In the controls, significant correlations were seen between different parameters of intake and the percentage of certain serum phospholipid fatty acids. These correlations in the patients were either absent or less marked. Conclusions Use in persons with CF of the energy intake to basal metabolic rate ratio, measurement of fecal fat and nitrogen at 72 hours and of urine nitrogen may be useful to validate dietary surveys. The serum phospholipid fatty acid profile, however, may be less useful for this purpose in these patients.