The structure of lipids deeply relates to its health function and metabolism. This type of study has been carried out using radio or stable isotope labeled lipids so far. Particularly, the method using deuterium (2H) labeled fatty acid and mass spectrometry developed by Emken et al. is excellent. However, the method cannot compare the migration and metabolism of labeled fatty acids, namely the front and back of fatty acid metabolism. In this paper, migration and metabolism of 2H and carbon thirteen (13C) labeled odd- and even-numbered fatty acids were examined using mice. The results revealed that the odd-numbered fatty acids were accumulated to the body fat. It was thought that low beta-oxidizability of odd-numbered fatty acid causes the result. The expired carbon dioxide (CO2) after administration of stable labeled fatty acid to mice was also examined using IR-MS. The carbon locating at carbonyl group in fatty acid firstly changed to CO2 and fatty acid labeled carbonyl with 13C forms 13CO2. IR-MS can quantify the amount of 13CO2 in expiration. The results also indicated low beta-oxidizability of odd-numbered fatty acid. The health functions of n-3 type fatty acids were compared among EPA (C20:5n-3), DPA (C22:5n-3), and DHA (C22:6n-3) to understand the relationship between the structure of fatty acid and health function. As the results, both numbers of double bonds and carbon numbers related to the health functions. Consequently, DPA expressed the medium health function among them in all the measurement parameters such as adiponectin, lipid profiles in blood and liver, etc.
