Gastric and Postgastric Processing of 13C Markers Renders the 13C Breath Test an Inappropriate Measurement Method for the Gastric Emptying of Lipid Emulsions in Healthy Adults.

Background: 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.Objective: The objective of this work was to investigate the validity of 13C BTs as a measure of fat GE rate in LEs.Methods: The lipophilic 13C octanoate (OCC) BT marker was investigated for fat GE with the hydrophilic 13C sodium acetate (ACC) and the triglyceride 13C 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/m2): 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 13CO2 excretion profiles was determined. The BT half-emptying times (BT T50) were validated with the MRI half-emptying time of the ingested fat volume (MRI T50).Results: The effect of LEs on 13CO2 excretion depended on the properties of the 13C marker. T50 for OCC was shorter by 98 min for LE1 than for LE4 (P < 0.001). Other markers showed either no LE dependency or a longer T50 for LE1 than for LE4. No difference in T50 between OCC and ACC was detected in LE1. In LE4, the T50 was longer by 154 min (P < 0.0001). There was some concordance between MRI T50 and OCC BT T50 for LE1 (rc = 0.7). No other marker showed any concordance with fat GE. 13C-Nuclear magnetic resonance in vitro findings were compatible with changes in the kinetics of phase transfer of OCC dependent on its protonation state.Conclusions: The structure of fat present in the stomach affects 13CO2 excretion. The chemical properties of the 13C marker and their gastric and postgastric interaction with fat renders 13CO2 excretion an inappropriate measure of LE emptying in healthy adults. This trial was registered at clinicaltrials.gov as NCT02226029 and NCT02602158.