Background: Fatty acid oxidation has frequently been measured using (13)C or (14)C labeled fatty acids. While providing valuable data, the breath test method is hindered by the need for a controlled environment to measure VCO(2) and collect frequent breath samples. Additionally, the CO(2) breath tests require the use of (13)C- or (14)C-acetate to correct for isotope exchange in the TCA cycle. We validated d(31)-palmitic acid for measuring dietary fat oxidation. When oxidized, the deuterium appears as water and mixes with the body water pool providing a cumulative record of fat oxidation.
Methods: The recovery of deuterium from d(31)-palmitic acid at 10 h post-dose was compared to that of (13)CO(2) from [1-(13)C]-palmitic acid in nine subjects (body mass index (BMI)=23.6+/-2.8; percentage body fat (%BF)=22.6+/-5.3; mean+/-s.d.). Subjects were studied at rest. [1-(13)C]-acetate (2 mg/kg) was dosed in a liquid breakfast. On a second day, [1-(13)C]-palmitic acid (10 mg/kg) and d(31)-palmitic acid (15 mg/kg) were dosed with the same liquid breakfast.
Results: Recovery of (13)CO(2) from [1-(13)C]-acetate at 10 h post-dose was 53.7+/-10.4%. Recovery of d(31)-palmitic acid was 13.2+/-7.7% (mean+/-s.d.) and [1-(13)C]-palmitic acid recovery was 6.4+/-3.6%. When the (13)C data was corrected for [1-(13)C]-acetate (Na salt) recovery, the mean difference in percentage recovery between the two tracers was 0.5+/-2.8% and cumulative recoveries through 10 h post-dose were highly correlated (y=1.045x - 0.47; r(2)=0.88, P<0.0002). Our data shows both labels to be equivalent in their ability to measure dietary fat oxidation in resting subjects.
Conclusions: The use of deuterium labeled palmitic acid eliminates the need for rigid control over the subjects' environment. Frequent sampling and measurement of VCO(2) are not needed for accurate calculation of percentage recovery of the deuterium label. In addition, the deuterium label has a decreased potential for isotopic exchange compared to (13)C or (14)C, so a recovery correction factor is probably not required.