Rates of Change in Tissue Fatty Acid Composition When Dietary Soybean Oil Is Switched to Olive Oil

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This experiment characterizes the time-dependent changes of phospholipids of liver microsomes, plasma, and triglycerides of adipose tissue when olive oil is substituted for soybean oil in the American Institute of Nutrition 93 Growth (AIN 93G) diet. After 2 weeks of acclimation with 7% soybean oil diet, 108 male Sprague-Dawley rats were randomly assigned to be fed diets with either 7% or 15% soybean oil or olive oil. Fatty acids of adipose, blood plasma, and liver microsomes were analyzed every four days for 4 weeks by gas chromatography. After 6 weeks of feeding, no differences in body weight or body composition were observed. The most profound changes occurred in the proportion of linoleic acid to oleic acid in the three tissues. The feeding regimens increased the ratio of oleic to linoleic acids by 6- to 14-fold in olive oil groups compared with soybean oil groups. The level of arachidonic acid declined in olive oil groups. In contrast, levels of n-3 series long chain fatty acids, eicosapentaenoic and docosahexaenoic acids, were higher in olive oil groups. The peroxidizability index, a measure of unsaturation, declined significantly in groups fed olive oil compared to soybean oil. These data indicate that substantial remodeling in fatty acid composition continues until 18-carbon precursors in adipose depots match the dietary pattern. The rate of change appears to be governed by the fractional exchange rate of adipose tissue, which is limited by the rates of lipolysis and daily fatty acid oxidation.