Chain shortening of palmitic acid in human subjects.

Chain shortening of palmitic acid was examined in vivo by comparing oxidation rates of [1-13C]palmitate vs [16-13C]palmitate fed to four male subjects consuming a high-fat diet. For 9 d subjects were fed a diet of normal foods providing an energy intake equal to their estimated requirements. The diet provided (as energy) approximately 14% protein, 46% carbohydrate, and 40% fat at a P:S ratio of 0.25. Analysis of breath 13CO2 enrichment on day 3 permitted analysis of background 13C contribution from the test diet alone. On days 4 and 7 either [1-13C]palmitic acid or [16-13C]palmitic acid (9-13.5 mg/kg body wt) was fed with the breakfast meal. The whole-body rate of oxidation of [1-13C]palmitic acid was significantly greater than that observed for [16-13C]palmitic acid. These results suggest that up to 34% of dietary palmitic acid consumed may be subjected to extramitochondrial chain shortening.