Is there an optimal dose for dietary linoleic acid? Lessons from essential fatty acid deficiency supplementation and adipocyte functions in rats.

Differential effects of n-3 and n-6 polyunsaturated fatty acids (PUFAs) have been demonstrated on adipose tissue physiology. Facing to the widely recognized beneficial effects of n-3 PUFAs, the n-6 PUFA effects remain controversial. Thus, we further analyzed the linoleic acid (LA) influence on adipocyte functions. To this aim, we treated by LA supplementation at three distinct doses (1, 2.5, or 5% of energy intake) rats with essential fatty acids deficiency (EFAD). PUFA composition was determined in blood and white adipose tissue (WAT), while lipolytic and lipogenic activities were measured in isolated adipocytes. EFAD rats exhibited reduced WAT mass and increased EFAD biomarkers. WAT mass was completely recovered after supplementation, irrespective of LA dose. However, neither body mass nor EFAD biomarkers returned to control with 1% LA, while LA abundance doubled in adipocytes from rats supplemented with 5% LA. Regarding lipolysis, 2.5% LA normalized the EFAD-induced alterations. A trend to decrease the maximal stimulation of lipolysis was observed with 1 and 5% LA. Regarding lipogenesis, the lower and higher LA doses increased basal activity and hampered insulin to further stimulate glucose incorporation into lipids whereas 2.5% LA normalized the basal or insulin-stimulated levels. Our results show that dietary linoleate at 2.5% restored anatomical, biochemical, and functional disturbances induced by EFAD. At higher dose, LA tended to reduce triacylglycerol breakdown, to increase triacylglycerol assembly, and to provoke insulin resistance. Therefore, LA influence on adipocyte functions does not appear to follow a typical dose-response relationship, adding further complexity to the definition of its dietary requirement.