Oléagineux, Corps gras, Lipides (Sep 2005)
Effet de la dose d’acide alpha-linolénique alimentaire sur le métabolisme lipidique
Abstract
The purpose of our study was to investigate the effects of high doses of ALA provided by linseed oil (containing 50% ALA) on its own bioavailability and that of its derivatives as well as on lipid metabolism. We investigated in male hamsters the dose/response effects of ALA over a broad range of supply as linseed oil (1, 10, 20 and 41% of total fatty acids, FA, or 0.4, 3.6, 6.7 and 14.6% of total energy intake). ALA was substituted for oleic acid in order to keep constant linoleic acid (LA) and saturated fatty acids which could interfere with the metabolism of n-3 PUFA and lipids, respectively. The capacity of ALA absorption, transport, storage and conversion into EPA had no limitation over the chosen range of dietary intake. However, dietary ALA failed to increase DHA content in plasma phospholipids. In parallel to the increase in EPA, arachidonic acid content decreased, resulting in an improved balance of 20 carbons FA. Moreover, in our atherogenic conditions, triglyceridemia decreased by 45% in response to 10% dietary ALA and was not affected by higher intakes. It was associated with lower hepatic activities of acetyl-CoA-carboxylase (up to – 29%) and malic enzyme (up to – 42%), which were negatively correlated to ALA intake (r2 = 0.33 and r2 = 0.38, respectively). Substitution of 10% ALA for oleic acid increased cholesterolemia by 15% but, as in TG, higher ALA intakes did not amplify the response. The highest ALA intake (40%) modified dramatically hepatobiliary metabolism of sterols. Thus, replacing 10% oleic acid by ALA is sufficient to improve its bioavailability and that of EPA, and to exert a beneficial hypotriglyceridemic effect, that may be counteracted by the slight increase in cholesterolemia. Higher intakes did not modify these parameters, but a very high dose resulted in adverse effects on sterol metabolism and does not seem appropriate for humans.
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