Gastric and Postgastric Processing of C Markers Renders the C Breath Test an Inappropriate Measurement Method for the Gastric Emptying of Lipid Emulsions in Healthy Adults.

Breath tests (BTs) present an alternative gastric-emptying (GE) measure. However, their efficacy in the measurement of the GE rate of lipid emulsions (LEs) is unknown. The objective of this work was to investigate the validity of C BTs as a measure of fat GE rate in LEs. The lipophilic C octanoate (OCC) BT marker was investigated for fat GE with the hydrophilic C sodium acetate (ACC) and the triglyceride C trioctanoin (TCC) markers as comparators. Data from 2 randomized studies were combined [50 healthy participants; 25 men, mean ± SD age: 23 ± 2.8 y; mean ± SD body mass index (in kg/m): 22.4 ± 1.7]. Each participant was given either an acid-stable LE (LE1) or an acid-unstable LE (LE4) at each visit. Twenty-three participants underwent simultaneous MRI. The effect of LEs on CO excretion profiles was determined. The BT half-emptying times (BT T) were validated with the MRI half-emptying time of the ingested fat volume (MRI T). The effect of LEs on CO excretion depended on the properties of the C marker. T for OCC was shorter by 98 min for LE1 than for LE4 ( < 0.001). Other markers showed either no LE dependency or a longer T for LE1 than for LE4. No difference in T between OCC and ACC was detected in LE1. In LE4, the T was longer by 154 min ( 0.0001). There was some concordance between MRI T and OCC BT T for LE1 ( = 0.7). No other marker showed any concordance with fat GE. C-Nuclear magnetic resonance in vitro findings were compatible with changes in the kinetics of phase transfer of OCC dependent on its protonation state. The structure of fat present in the stomach affects CO excretion. The chemical properties of the C marker and their gastric and postgastric interaction with fat renders CO excretion an inappropriate measure of LE emptying in healthy adults. This trial was registered at clinicaltrials.gov as NCT02226029 and NCT02602158.