| Summary: | To assess the influence of dietary fat composition on postprandial oxidation of
dietary myristic acid (MA), palmitic acid (PA) and other substrates, healthy males
(n=8) consumed prepared solid food diets containing 22% of energy as butter or
tallow. Using a randomized cross-over design, subjects were prefed 11 day test diets
which were identical in nutrient content except for the specific fat treatment. The
diets provided 40%, 45%, and 15% of energy as fat, carbohydrate and protein,
respectively, and were fed at a level equivalent to calculated energy requirements.
On day 8 and day 11 of each diet cycle, a randomly assigned bolus of [1-¹³C]MA or
[1-¹³C]PA (20 mg/kg body weight) was ingested with the breakfast meal. Hourly
breath samples were collected for 9 hours thereafter and ¹³C0₂ enrichment was
determined using isotope ratio mass spectrometry. Continuous respiratory gas
exchange was also monitored and carbohydrate oxidation, fat oxidation and energy
expenditure were determined. Treatment fat did not influence the fractional oxidation
of dietary [1-¹³C]MA (% dose/9 hours; x±SEM; 7.1±1.0% and 8.6±0.9% after the
butter and tallow meal, respectively) or [1-¹³C]PA (3.3±0.7% and 3.0±0.9% after the
butter and tallow meal, respectively) (P<0.01, MA versus PA). MA contents of the
butter and tallow meals were 4.6 g and 2.4 g, respectively, while the PA contents were
13.6 g and 11.2 g, respectively. While net dietary MA oxidation, calculated as the
product of percent oxidation * meal fatty acid content, was greater (p<0.05) after the
butter (329±45 mg) compared to tallow (212±25 mg) breakfast, no difference in net
oxidation of dietary PA was observed between butter (441 ±99 mg) and tallow (348±95 mg) meals. Overall, dietary MA or PA accounted for less than 1% of fat oxidized for
9 hours postprandial. Cumulative postprandial energy expenditure (kcal/9 hours;
783±26 kcal and 781±31 kcal after the butter and tallow meal, respectively),
cumulative postprandial fat oxidation (g/9 hours; 46±3 g and 44±4 g after the butter
and tallow meal, respectively), and cumulative postprandial carbohydrate oxidation
(g/9 hours; 85±8 g and 89±7 g after the butter and tallow meal, respectively) did not
differ due to fat treatment. These findings suggest that the percent oxidation of MA
and PA within a meal is independent of the blend of fatty acids consumed. However,
it is markedly enhanced with decreasing chain length. Conversely, net oxidation of
fatty acids contained within a meal is proportional to the mixture of fatty acids
contained therein. === Land and Food Systems, Faculty of === Graduate
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