UTILIZATION OF MYRISTIC AND PALMITIC ACID IN HUMANS FED DIFFERENT DIETARY FATS

To assess the influence of dietary fat composition on the contribution of dietary myristic and palmitic acid to total fat oxidation and ener gy production, eight healthy men consumed diets containing 40% of tota l energy as fat, largely as either butter, tallow or corn oil, for 11 days. On days 8 and 11 of each diet, [1-C-13]-myristic or [1-C-13]-pal mitic acid (20 mg kg(-1) body weight) was ingested mixed with the test breakfast meal. Respiratory gas exchange was measured before, and for 9 h after, consumption of the meal. Breath (CO2)-C-13 enrichments wer e determined hourly by isotope ratio mass spectrometry. Cumulative 9-h percentage oxidation of dietary myristic acid exceeded that of palmit ic acid (P < 0.01), but neither was influenced by fat treatment [n = 8 , 7.1% (1.0) (SEM), 8.6% (0.9) and 8.9% (0.6) of dietary myristic acid and 3.3% (0.7), 3.0% (0.9), and 2.5% (0.6) of dietary palmitic acid f rom butter, tallow and corn oil meals respectively]. Net dietary myris tic acid oxidation was greater (P < 0.05) after consumption of the mea l high in butter than after consumption of other fats. Net dietary pal mitic acid oxidation was similar after consumption of all test meals. Precedent fat treatment had no measurable effect on net fat or carbohy drate oxidation or energy expenditure. The overall contribution of die tary myristic or palmitic acid to total fat oxidation did not exceed 1 % over 9 h for any dietary fat. These results suggest that, although d ietary fatty acid content is the principal determinant of net dietary fatty acid oxidation, dietary fat sources with moderate differences in fat composition do not measurably alter total energy or substrate uti lization after a meal.