The Majority of Dietary Linoleate in Growing Rats is β-Oxidized or Stored in Visceral Fat ,

Abstract

On a quantitative, whole-body basis, little is known about the amount of linoleate that is converted to arachidonate or the partitioning of linoleate and its longer-chain derivatives among lean and fat tissues. The aim of the present study was to examine linoleate balance and organ partitioning in rats consuming a low but adequate level of linoleate. Weanling male Sprague-Dawley rats were given free access to a semipurified diet containing 2.3% of energy as linoleate. Food intake, fecal output and body weight gain were measured for 26 d. Whole-body fatty acid balance analysis showed that 75.5% of the linoleate consumed disappeared (apparently by β-oxidation), 18.7% was accumulated as linoleate, 3.0% was converted to (n-6) longer-chain polyunsaturated fatty acids, and 1.2% was excreted in the feces. Visceral fat contained 64% of the accumulated linoleate, and 23% was in lean tissues. Comparable values for α-linolenate were as follows: disappearance (84.9%), accumulation (10.9%), excretion in the feces (2.2%), and conversion to (n-3) longer-chain polyunsaturated fatty acids (1.4%). Visceral fat contained 67% of the accumulated α-linolenate, and 23% was in lean tissues. Visceral fat also accumulated 26% of newly synthesized (n-6) longer-chain polyunsaturated fatty acids and 31% of the (n-3) longer-chain polyunsaturated fatty acids. Thus, only 6.5% of dietary linoleate consumed at a low but adequate level for rats appeared in lean tissues as linoleate or its fatty acid metabolites; the rest was β-oxidized or stored in fat, mostly in visceral fat. These results lead us to speculate whether losses through β-oxidation contribute to the recommended intake for linoleate in growing rats.