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 [Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions]

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 (r_c = 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.

From: Parker, H. L., Liu, D., Curcic, J., Ebert, M.-O., Schwizer, W., Fried, M., Steingoetter, A. http://jn.nutrition.org/cgi/content/short/147/7/1258?rss=1