Lipid Metabolic Response of Domestic Felines to Dietary Omega-6 and Omega-3 Polyunsaturated Fatty Acids
Despite the unique aspects of feline fatty acid metabolism, few studies have systematically characterized this species' response to dietary polyunsaturated fatty acids. Consequently, this study was designed to investigate effects of diets varying only in fatty acid (FA) composition on triacylglycerol (TAG), total cholesterol (TC), non-esterified fatty acid (NEFA), lipoprotein-cholesterol distributions, and plasma phospholipids (PL). Twenty nine clinically normal, sexually intact, young adult female cats were randomized into three groups (n=9,10,10). Each group was fed a complete and balanced, commercial, dry extruded type basal diet, supplemented with 8g oil/100g diet. The oils used and the resulting diets fed were: high-oleic sunflower oil (H diet) with 82% oleic acid, Menhaden fish oil (M diet) with high amounts of long chain n3 fatty acids (LCn3FA), and safflower oil (S diet) with 75% linoleic acid. Arachidonic acid (20:4n6) content of the diets was: 0.03 for H, 0.09 for M, and 0.03 for S (g FA/kg diet). Diets were fed for 28 days with blood collections on days 0, 14, and 28. Using PROC MIXED analysis in SAS with p < 0.05 as significant, the M diet showed a significant TAG lowering effect despite the already low normal feline TAG levels. No main time or diet effects were found with TC or NEFA. Lipoprotein electrophoresis revealed a significant lowering of the pre-beta band (i.e., TAG-rich VLDL) in the M group consistent with plasma TAG lowering. Plasma PL FA profile revealed statistically significant diet and time effects in addition to time x diet interactions. Many of these changes were significantly different at day 14, but by day 28 were less pronounced indicating a transitional metabolic response at day 14 versus day 28. Anticipated diet effects included: statistically significant accumulation of 18:1n9 in the H group, 18:2n6 in the S group, and LCn3FA in the M group. Despite high dietary 18:2n6 in the S group PL-20:4n6 was not increased over the other groups. In comparison to other species, only modest amounts of PL-20:4n6 were found in these cats. Furthermore, a significant increase in the in 20:2n6 in the S group demonstrated that chain elongation of excess 18:2n6 occurred in deference to its Δ6 desaturation. These findings further substantiate the known low Δ6 desaturase activity of cats. Similarly, increased relative amounts of 20:1n9 in the M diet resulted in its chain elongation and accumulation to 24:1n9 in the M group. It is noteworthy that the M diet did not blunt incorporation of 20:4n6 into PLs. This effect was minimized because fish oil provided 3 times more 20:4n6 than the vegetable oils, and cats have low Δ6 conversion. Additionally, blunting of 20:4n6 into PL's was not seen due to tissue 20:4n6 content being diet dependent. In conclusion, fish oil results in PL-LCn3FA enrichment without negative effects on 20:4n6 and lowers plasma TAG levels. Whether TAG lowering in normal cats is beneficial is unknown at this time although n3 FA's may help treat hepatic lipidosis in this species.