Comparison of catabolic rates of fatty acids using stable isotope and isotope‐ratio mass spectrometry

Abstract

AbstractThe catabolic rates of individual fatty acids in mice were compared using stable isotope (13C)‐labeled fatty acids and isotope‐ratio mass spectrometry (IRMS). The catabolic rates were evaluated from the ratio of 13C and 12C in carbon dioxide expired by mice. The results showed that the catabolic rate of octanoic acid is three times faster than that of palmitic acid. This result is consistent with previous reports using radioisotope 14C showing that medium‐chain fatty acids are more easily beta‐oxidized than long‐chain fatty acids. The catabolic rates of odd‐numbered fatty acids such as pentadecanoic acid and heptadecanoic acid were significantly lower compared to those of even‐numbered fatty acids such as palmitic acid. These findings support previous reports that show odd‐numbered fatty acids easily accumulating in body fat. The high accumulation of odd‐numbered fatty acids in body fat thus directly reflects a low degree of beta‐oxidization. The combination of stable isotope‐labeled compounds and IRMS serves as a powerful tool in lipid analysis.