Validation of deuterium labeled fatty acids for the measurement of dietary fat oxidation: a method for measuring fat-oxidation in free-living subjects

Abstract

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 VCO₂ and collect frequent breath samples. Additionally, the CO₂ breath tests require the use of ¹³ C- or ¹⁴ C-acetate to correct for isotope exchange in the TCA cycle. We validated d₃₁ -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 d₃₁ -palmitic acid at 10 h post-dose was compared to that of ¹³ CO₂ 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 d₃₁ -palmitic acid (15 mg/kg) were dosed with the same liquid breakfast. RESULTS:: Recovery of ¹³ CO₂ from [1-¹³ C]-acetate at 10 h post-dose was 53.7±10.4%. Recovery of d₃₁ -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; r² = 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 VCO₂ 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. INTERNATIONAL JOURNAL OF OBESITY: (2001) 25, 1240-1245