Dietary conjugated linoleic acid reduces rat adipose tissue cell size rather than cell number

We investigated the basis for the reduction in fat pad size in rats fed con jugated linoleic acid (CLA). In the first study, growing female Sprague-Daw ley rats (initial weight150 g) were fed diets containing 0, 0.25 and 0.5 g/ 100 g diet of a purified (97% GLA) and 0.5% of a feed-grade (55% CLA) sourc e of CLA for 5 wk to determine the effects on growth performance and fat ma ss. There was no effect of CLA on growth rate or food intake. Dietary CLA r educed retroperitoneal fat pad weight 13, 25 and 32% in rats fed 0.25 and 0 .5% of the pure CLA and 0.5% of the feed-grade CLA, respectively (P < 0.05) . Similar effects were observed in the parametrial fat pad. The reduced pad size was due to smaller adipocyte size rather than a reduced cell number. Relative to the control group, mean cell volume was 15, 28 and 29% tower in tissue from rats fed 0.25 and 0.5% of the pure CLA and 0.5% of the feed-gr ade CLA, respectively (P < 0.01). in the second study, rats were fed CLA (0 vs. 0.5%) for 7 or 49 d. Reductions in fat pad weight were observed within 7 d. In addition, the effects of CLA on energy metabolism were studied in the chronically fed rats. There were no significant effects of CLA on oxyge n consumption, CO2 or heat production. During wk 4 of feeding, but not at o ther times, there was a 5% lower respiratory quotient in CLA-fed rats (P < 0.05). There was a time-dependent accumulation of CLA in adipose tissue and a decrease in monounsaturated fatty acids. These results suggest that the reduction in fat mass in rats fed CLA can be accounted for by a reduction i n cell size rather than a change in cell number.