Fatty acids in triacylglycerol (TAG) are catabolized after digestion. However, the catabolic rates of several fatty acids bound to the α (sn-1, 3) or β (sn-2) position of TAG have not been thoroughly compared. In this study, the catabolic rates of 13 C-labeled palmitic acid, oleic acid, linoleic acid, α-linolenic acid, eicosapentaenoic acid (EPA), or docosahexaenoic acid (DHA) bound to the α and β position of TAG were compared using isotope ratio mass spectrometry. The catabolic rates of the studied fatty acids were evaluated using the ratio of 13 C and 12 C in carbon dioxide expired from mice. The results indicated that palmitic acid, oleic acid, or α-linolenic acid bound to the β position was slowly catabolized for a long duration compared to that when bound to the α position. In contrast, EPA bound to the β position was quickly catabolized, and EPA bound to the α position was slowly catabolized for a long time. For linoleic acid or DHA, no difference in the catabolic rates was detected between the binding positions in TAG. Furthermore, EPA and DHA were less catabolized than the other fatty acids. These results indicate that the catabolic rates of fatty acids are influenced by their binding positions in TAG and that this influence on the catabolic rate differed depending on the fatty acid species.

The absorption efficacies and catabolic rates of fatty acids are affected by their binding position on triacylglycerol (TAG). However, the kind of effect calcium treatment has on the catabolism of fatty acids is unclear. In this study, the catabolic rates of 13 C-labeled palmitic acid, oleic acid, and linoleic acid bound to sn-1, 3 (α) and sn-2 (β) position of TAG in the presence of calcium were compared using isotope ratio mass spectrometry. The catabolic rates of 13 C-labeled fatty acids were evaluated using the ratio of 13 C to 12 C in the carbon dioxide expired by mice. The catabolic rate of palmitic acid bound to the α position was significantly lower than that of palmitic acid bound to the β position of TAG. The rates of 13 CO 2 formation from palmitic acid at the β position remained higher for a long time. In contrast, oleic and linoleic acids at the α position were as well catabolized as those at the β position. These results indicate that in the presence of calcium, the saturated fatty acid bound to the β position is highly catabolized, whereas that bound to the α position is not well catabolized. Saturated fatty acid at the α position is hydrolyzed by pancreatic lipase to promptly form insoluble complexes with calcium, which are excreted from the body, and thereby reducing the catabolic rate of these fatty acids.

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