THE EFFECTS OF TRANS FATTY ACIDS ON ESSENTIAL FATTY ACID METABOLISM

The effects of graded levels of dietary t,t-18:2, a fatty acid isomer formed during hydrogenation of vegetable oils, on enzymes involved in essential fatty acid metabolism was tested in rats.;Liver levels of t,t 18:2 increased linearly from 0 to 1.6 mg/g liver as dietary t,t 18:2 was increased from 0 to 50 percent. This inhibited the conversion of linoleic to arachidonic acid in liver tissue and resulted in an increase in linoleic acid levels from 1.2 to 3.1 mg/g liver, while arachidonic acid levels decreased from 3.9 to 1.9 mg/g liver as dietary t,t 18:2 levels were increased from 0 to 50 percent of fat. This inhibition was shown to be caused by the specific inhibition of (DELTA)6 desaturase by t,t 18:2. The (DELTA)6 desaturase activity decreased by half as dietary t,t 18:2 levels were increased from 0 to 50 percent of fat. It was verified by separate in vitro tests that t,t-18:2 could specifically inhibit (DELTA)6 desaturase. It was also established that there was sufficient t,t 18:2 present in the free fatty acids of liver microsomes to cause significant inhibition of (DELTA)6 desaturase activity.;The liver levels of t,t 18:2 and (DELTA)6 desaturase levels were also tested over the duration of the study. It was observed that tissue levels of t,t 18:2 increased slightly over the course of the study for all treatments except when rats were fed highest levels of t,t 18:2 (50% of fat). Rats on this treatment had 1.6 mg t,t 18:2/g liver tissue after both four and eleven weeks. This may indicate that a tissue saturation level had been reached by four weeks on the high trans diets. However, (DELTA)6 desaturase levels in livers were not significantly different over the course of the study for any of the rats fed diets containing t,t 18:2.;The (DELTA)5 desaturase activities increased as dietary t,t 18:2 levels were increased, although the relationship was not strictly linear. Rats fed 50% of t,t 18:2 in the dietary fat had 70% higher (DELTA)5 desaturase activities than rats fed diets where t,t 18:2 was omitted.;Purified diets containing 11 percent of calories as fat were fed. Linoleic acid (1.1 cal. %) was present in all diets, and the dietary fat also contained 0, 5, 10, 20 and 50 percent (by wt.) of t,t 18:2.;These results are significant because they indicate that t,t 18:2 can inhibit (DELTA)6 desaturase and thereby decrease levels of gamma homo linolenic acid and arachidonic acid in body tissues.;The results of this study indicate that dietary t,t 18:2, at levels consumed in the American diet, should not significantly inhibit essential fatty acid metabolism. However, caution is advised, since a five fold increase in dietary t,t 18:2 significantly inhibited the (DELTA)6 desaturase and caused a 30 percent decrease in arachidonic acid levels in the presence of low levels of dietary essential fatty acids.