Brown fat thermogenesis in rats fed high-fat diets enriched with n-3 polyunsaturated fatty acids.

Objective: To examine the possible involvement of an increase in diet-induced thermogenesis from brown adipose tissue (BAT) in the n-3 polyunsaturated fatty acids (n-3 PUFA) induced limitation of the development of white fat pads during high-fat feeding.

Design: Rats fed for four weeks on a low-fat/high-carbohydrate diet (C group) or high-fat diet without n-3 PUFA (REF group), with eicosapentaenoic acid (EPA group), with docosahexaenoic acid (DHA group) or with a mixture of these two fatty acids (MIX group).

Measurements: Epididymal and retroperitoneal fat pad mass, BAT composition, Guanosine 5'-diphosphate (GDP) binding and uncoupling protein (UCP) content were measured in the five groups of rats.

Results: The masses of retroperitoneal and epididymal white fat pads were lower in the groups fed n-3 PUFA than in the C and REF groups. The total BAT GDP binding was 1.6 times higher in the MIX and EPA groups than in the REF group. The BAT from the EPA group presented an enrichment in mitochondria compared to the C and REF groups whereas the BAT from the DHA and REF groups presented a hyperplasia and an increase in thermogenic activity of the mitochondria compared to the C group. The higher thermogenic activity of BAT was observed in the MIX group and is due to hyperplasia and to an increase in thermogenic activity of mitochondria.

Conclusions: n-3 PUFA induce a marked stimulation of BAT thermogenic activity without changes in the UCP content compared to a high-fat diet without n-3 PUFA. The mixture of EPA and DHA has the more pronounced effect while EPA and DHA seem to act in synergy on BAT thermogenesis via different mechanisms.