Absorption of 13C-labeled stearic, oleic, and linoleic acids in humans: application to breath tests

Intestinal absorption of ingested [1-13C]stearic, [1-13C]oleic, and [1-13C]linoleic acid was compared in six healthy men. A bolus of each [1-13C]-labeled fatty acid was ingested in random order at 72-hour intervals with the breakfast meal. Subjects consumed fixed diets during a 9-day fecal collection period. Pooled 9-day fecal samples were homogenized and total fat extracted. Fat extracts were saponified and methylated, and individual fatty acids were quantitated by gas-liquid chromatography. Preparative high-performance liquid chromatography was used to obtain fractions containing stearic, oleic, and linoleic acid for combustion to CO2 and assay of 13C enrichment over background. Prelabel period 24-hour samples were treated similarly to measure background 13C abundance. Total fatty acid and stearic, oleic, and linoleic acid excretion (+/- SEM) in the six volunteers over the 9-day period was 41.5 +/- 7.3, 10.0 +/- 1.3, 8.8 +/- 2.9, and 0.8 +/- 0.1 mg/day/kg body weight, respectively. The absorption efficiency for [1-13C]stearic, [1-13C]oleic, and [1-13C]linoleic acid was 78.0% +/- 4.5%, 97.2% +/- 1.7%, and 99.9% +/- 0.1%, respectively. The reduced absorption of [1-13C]stearic acid observed emphasizes the importance of correcting breath test oxidation data for fecal loss of 13C substrate. The potential application of our method to other areas of intermediary metabolism is discussed.