Maldigestion and malabsorption of 13C labelled tripalmitin in gastrostomy-fed patients with cystic fibrosis

Background & aims: Some patients with cystic fibrosis continue to have excessive losses of stool lipid, despite the use of pancreatic enzyme replacement therapy to improve digestion. The aim of this study was to explore the residual capacity of the gastrointestinal tract to digest and absorb dietary lipid using stable isotopic methodology in ten patients with cystic fibrosis who were gastrostomy fed in comparison to eight healthy children. We sought to test the hypothesis that a reduction in the availability of dietary lipid may arise from malabsorption of the products of digestion, rather than maldigestion alone. Methods: All subjects consumed [1,1,1-13C] tripalmitin (10 mg/kg body weight) with a standardised meal but the patients with cystic fibrosis did not take their habitual pancreatic enzymes. Total enrichment of 13C was measured by isotope ratio mass spectrometry in stools collected over 3 days. Maldigestion and malabsorption was differentiated by measuring 13C-label excretion in stool triglyceride and fatty acid fractions, respectively. Results: The patients with cystic fibrosis had elevated 13C-label losses in total stools (56.7%, 6.8–77.9%)(median and range; % administered dose), triglyceride (6.6%, 0–31.2%) and fatty acid (16.7%, 3.4–50.3%) fractions compared to healthy children (1.9%, 0–10.9%, P<0.001; triglyceride: 0.2%, 0–0.6%, P<0.01; fatty acid 0.9%, 0–6.5%, P<0.001). Conclusions: These results highlight differences between gastrostomy fed patients with cystic fibrosis to both digest and absorb dietary lipid. There is a need to extend these observations and apply this approach to patients both with and without pancreatic enzyme replacement therapy.