AIMTo examine the gastrointestinal handling and metabolic disposal of emulsified [1-¹³C]palmitic acid esterified into a triglyceride in nine healthy children and seven patients with cystic fibrosis on enzyme replacement treatment.
METHODSAfter an overnight fast, each child was given 10 mg/kg body weight
[1,1,1-¹³C]tripalmitin with a standardised test meal of low natural ¹³C abundance. The total enrichment of ¹³C was measured using isotope ratio mass spectrometry in stool collected for a period of up to five days and in breath samples collected over a 24 hour period.
RESULTSThe mean proportion of administered ¹³C label excreted in stool was 6% (range, 1-12.7%) in healthy children and 24.6% (range, 0-64%) in patients with cystic fibrosis. Healthy children excreted 31.3% of the administered label on their breath (range, 14.2-42.9%). Correcting the excretion of administered ¹³C label on the breath for differences in digestion and absorption in patients with cystic fibrosis increased the difference between individuals from 0-31.3% of administered dose (mean, 17.9%) to 0-49.1% of absorbed dose (mean, 23.2%) and was poorly related to the amount of ¹³C label in stool.
CONCLUSIONMeasurements of breath ¹³CO₂ do not consistently reflect the gastrointestinal handling of emulsified ¹³C labelled tripalmitin because of differences in digestion and absorption in cystic fibrosis. Further studies need to examine whether "breath tests" alone can predict with confidence the gastrointestinal handling of other ¹³C labelled triglycerides and fatty acids.

Keywords: fatty acids; absorption; metabolism; stable isotopes; cystic fibrosis