Effect of butter compared with tallow consumption on postprandial oxidation of myristic and palmitic acids

To assess the influence of dietary fat composition on rates of oxidation of dietary myristic (MA) and palmitic (PA) acids, eight healthy males consumed prepared solid-food diets for 11 d with 40% of total energy as fat. Fifty-five percent of the energy obtained in the form of fat was provided as butter or beef tallow. On days 8 and 11 of each diet cycle, 20 mg/kg body wt of either [1-(13)C]MA or [1-(13)C]PA was ingested with breakfast. Hourly breath samples were collected over 9 h thereafter and 13CO2 enrichments were determined by using isotope-ratio mass spectrometry. The percentage of [13C]MA appearing in breath carbon dioxide over 9 h was more than twofold that of PA (P < 0.01). Diet fat composition did not influence the mean (+/- SEM) percentage 13C recovered over 9 h from either labeled MA (7.1 +/- 1.0% compared with 8.6 +/- 0.9% for butter and tallow, respectively) or PA (3.3 +/- 0.7% compared with 3.0 +/- 0.9% for butter and tallow, respectively). However, net MA oxidation, calculated as the percent recovery of fatty acids in the meal, was greater (P < 0.05) after the butter (329 +/- 45 mg) than after the tallow (212 +/- 25 mg) breakfast. In contrast, no difference was observed in net oxidation of dietary PA between butter (441 +/- 99 mg) and tallow (348 +/- 95 mg) meals. In conclusion, there was no effect of varying the dietary content of MA and PA on fractional oxidation; consequently, net oxidation of these fatty acids was proportional to their concentration within the diet.