| Comparative oxidation and absorption of stearic, oleic and linoleic acids was measured to determine the effect of the degree of dietary fatty acid unsaturation on whole body fat utilization in humans. An experimental diet designed of normal foods to contain 40% fat and a P:S ratio of 0.25 was utilized throughout the studies. This diet was fed to healthy males at a level equal to estimated energy requirements. Initially ('13)CO(,2) breath test methodology was applied to 4 subjects in the fed state by characterizing diet induced changes in ('13)CO(,2) enrichment. One subject was tested 4 times. Between subject variation, 0.00062 atom % (SE, n = 4) was greater than within subject variation, 0.00032 atom % (SE,n = 4). Subsequently 6 subjects were fed the test diet for 16 days. On days 8, 11 and 14 1-('13)C stearic (20 mg/kg), 1-('13)C oleic (10 mg/kg) or 1-('13)C linoleic (10 mg/kg) acids were given with the test diet breakfast. ('13)CO(,2) production was measured over 9 hours. The ('13)CO(,2) produced from diet alone, as measured on day 6, was subtracted from that generated by 1-('13)C fatty acids for each subject. For fatty acids contained in the test breakfast, oleic, linoleic and stearic acids showed differences in oxidation beginning 3 hours after feeding and by 9 hr. 42.7 (+OR-) 6.7, 9.5 (+OR-) 1.5 and 3.1 (+OR-) 1.0 mg/kg subject body weight (x (+OR-) SD, n = 6) of each substrate respectively, was oxidized. Total dietary fat absorbed by subjects over days 8-16 was 97.0 (+OR-) 2.0%. 1-('13)C -stearic, -oleic and -linoleic acid absorption were 78.0 (+OR-) 11.0, 97.2 (+OR-) 4.1 and 99.9 (+OR-) 0.1% (x (+OR-) SD, n = 6), respectively. Both dietary and 1-('13)C stearic acids were less well absorbed than either oleic or linoleic acids. These findings indicate that the degree of long chain fatty acid unsaturation affects the rate of absorption and oxidation of dietary fat in humans. |
