Absorption and lymphatic transport of interesterified or mixed fats rich in saturated fatty acids and their effect on tissue lipids

Interesterification of fully hydrogenated plant oils with liquid oils has been used as an alternative to partial hydrogenation to produce a zero-trans solid fat due to recent reports of unfavorable effects of dietary trans fatty acids on serum cholesterol levels. Present study was carried out to examine absorption of saturated fatty acids derived from mixed and interesterified fats and their effects on concentration of serum cholesterol. Dietary fats consisted of tripalmitin or tristearin: high oleic safflower oil: safflower oil ratios of 44.4:35.3:20.3 or their interesterified products; a melting point of the interesterified fat was lower than that of the corresponding mixed fats. When rats were fed these-fat containing diets for three wks, absorption rate estimated by excretion of fatty acids into feces was higher in interesterified fat-fed rats than in the corresponding mixed fat-fed rats. This improved absorption was accompanied by an increased concentration of liver triacylglycerols and an increased proportion of stearic acid in the adipose tissue and an increased proportion of oleic acid in serum and liver. Dietary fats exerted no significant effect on the liver or serum cholesterol concentration or the excretion of neutral or acidic steroids into feces. In contrast to dietary fat absorption, administration of the mixed and interesterified fats, emulsified with taurocholate and albumin, into stomach of rats cannulated with thoracic lymph duct resulted in lymphatic triacylglycerols with a comparable transport rate and with a similar fatty acid composition at each position of triacylglycerols. These results demonstrate that interesterification improves absorption of dietary fats, possibly by facilitating emulsification of saturated fats, but seems not to exert any adverse effects on the concentration of serum and liver cholesterol.