Journal Name:
Am J Clin Nutr
Article Title:
Differential oxidation of individual dietary fatty acids in humans.
Date Written:
2000
Volume:
72
Number:
4
Page:
905
Author(s):
DeLany, J.P.; Windhauser, M.M.; Champagne, C.M.; Bray, G.A.
Article:
Variety in fatty acid structure resulting from differences in chain length, degree of unsaturation, and position and stereoisomeric configuration of the double bonds may affect the rate of fatty acid oxidation potentially leading to differing rates of fat accumulation . Several studies in humans in which 13Clabeled substrates were fed have reported oxidation of oleate (18:1n-9) to be greater than that of linoleate (18:2n-6), which was greater than that of stearate (18:0). It would appear that short- and medium-chain fatty acids oleate and linolenate (ALA) are oxidized rapidly, whereas the long chain saturated fatty acids palmitate (16:0) and stearate are oxidized more slowly. Data regarding the effect of label position in humans are lacking. The current study was undertaken to examine fatty acid oxidation in humans by using fatty acids labeled with 13C in the carboxyl or methyl position and to examine the role that chain length, degree of unsaturation, and stereoisomeric configuration of the double bonds play in determining the relative rates of oxidation of individual fatty acids.
Fatty acid oxidation was examined in men consuming a weight-maintenance diet containing 40% of energy as fat. After consuming the diet for 1 week, subjects were fed fatty acids labeled with 13C in the methyl or carboxyl position (10 mg/kg body wt). The fatty acids fed in random order were laurate, palmitate, stearate, oleate, elaidate (the trans isomer of oleate), linoleate, and linolenate blended in a hot liquid meal. Breath samples were collected for the next 9 h and the oxidation of each fatty acid was assessed by examining liberated 13CO2 in breath. In this study, oxidation of saturated fatty acids decreased with increasing carbon length (laurate > palmitate > stearate). The relation between oxidation and fatty acid carbon length was highly significant. There was a nearly perfect linear relation between oxidation and the number of double bonds for stearate, oleate, and linolenate. The medium-chain fatty acid, laurate, was oxidized more rapidly than was oleate, which was oxidized faster than was palmitate. Oleate and linoleate were oxidized similarly, whereas stearate was the least oxidized. A relatively high oxidation of the polyunsaturated fatty acids linolenate and linoleate was seen. Unsaturated fatty acids, particularly at the usual low dietary levels, may be transported from the intestine directly to the liver via the portal system and used for fuel. *The rates of oxidation of individual dietary fatty acids may relate to differences in weight gain observed when different types of fat are fed to animals. As unsaturated fatty acids are more highly oxidized than are the saturated fatty acids; mice fed corn oil have been shown to gain less weight than mice fed beef tallow, which is high in saturated fatty acids. The finding in this study that ALA is highly oxidized is consistent with this idea. In summary, this study showed that ALA was the most highly oxidized and linoleate was the least oxidized fatty acid. MUFAs are fairly well oxidized. These observations may be relevant to future research in canola oil as differences in the rates of oxidation of individual fatty acids may play a role in human obesity.
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