The aim of this study was to assess the interindividual variability of chylomicron  -carotene response to a pharmacological load of  -carotene in the population, to identify the mechanisms responsible for this variability, and to evaluate its consequences on  -carotene status and metabolism. The variability, as estimated by the 3-h chylomicron  -carotene response to 120 mg  -carotene in 79 healthy male volunteers, was high (CV ؍ 61%), but it was unimodal and all the subjects had detectable chylomicron  -carotene. In 16 subjects randomly selected among the 79, the interindividual variability of the triglyceride-adjusted chylomicron (  -carotene ؉ retinyl palmitate) response (0-12.5 h area under the curve) was high (CV ؍ 54%), suggesting that there is a high interindividual variability in the efficiency of intestinal absorption of  -carotene. The chylomicron  -carotene response was correlated ( r ؍ 0.50, P Ͻ 0.05) with the chylomicron triglyceride response. The carotene status, as assessed by  -carotene concentration in buccal mucosal cells, was correlated ( r ϭ 0.73, P Ͻ 0.05) with the triglyceride-adjusted chylomicron  -carotene response, i.e., with the ability to respond to  -carotene. The triglyceride-adjusted chylomicron retinyl-palmitate response was correlated ( r ؍ 0.55, P Ͻ 0.05) with the triglycerideadjusted chylomicron  -carotene response. Plasma all-trans retinoic acid slightly, but significantly, increased ( ؉ 40%) 3 h after the  -carotene load, but this increase was not related to the triglyceride-adjusted  -carotene response. In conclusion, the ability to respond to  -carotene is highly variable, but there is probably a very small proportion of true non-responders to pharmacological doses of  -carotene in the healthy population. This variability is apparently mainly due to interindividual differences in the efficiency of intestinal absorption of  -carotene and in chylomicron metabolism. The ability to respond to  -carotene can affect the carotene status and the provitamin A activity of  -carotene, but it has apparently no effect on the amount of retinoic acid appearing in the plasma after the ingestion of a pharmacological dose of  -carotene.
pourcentage d'AET du régime alimentaire pourraient être définies comme suit : 11-16 % (soit 28 g à 44 g) d'acide oléique, 4-6 % (soit 9 g à 13 g) d'acide linoléique, 1 % (soit 1,5 g à 3 g) d'alphalinolénique (pour 60 % en position sn2). Soit des rapports 18:1/18:2n-6/18:3n-3 de l'ordre de 11-16/4-6/1 en % de l'AET. Summary :Oleic, linoleic and linolenic acids from vegetable oils: where are the limits for beneficial effects on lipemia and athero-thrombotic parameters in humans? Cardiovascular disease is the number one public health problem in western countries. Recent data showed that diets including 10 to 13% of oleic acid in the total caloric intake could protect from new cardio-vascular events [8], but increasing oleic acid intake to more than 20% of the total caloric intake could limit this beneficial effect by inducing an increase of LDL-C [21,34]. Grundy, in an attempt to clarify the desirable ratio of saturated versus unsaturated (mono and poly) fatty acids, concluded in 1997 to "insufficient data for recommended oleic intake", and proposed for the moment 15-16% as a "reasonable compromise". The objective of our study was to define the proper ratio between oleic, linoleic and alpha-linolenic (OL/LA/ALA ratio) and to validate dietary levels of oleic acid after stabilisation of the linoleic/alphalinolenic ratio in the diet of normolipidemic male subjects (n=40). In order to reach 11, 13 and 16% of oleic acid of the total energy (TE) intake, sunflower, high oleic sunflower (HOSO) and rapeseed oils were combined to obtain specific blends adjusted to the FA intake proposed in the protocol. Each of these 3 diets (11, 13, 16% oleic diets) was maintained for 16 weeks and the clearance of a fatty meal (1,000 kcal, 62.5% fat) was tested during 8 h postprandially at the end of each period. The results indicated that the stability of fasting and postprandial plasma atherogenic parameters was maintained to favorable levels. There were no statistical differences of the effects of the 11, 13, 16% oleic acid diets evaluated on fasting LDL-C, Non-HDL-C, HDL-C, TG, ApoB, ApoAI or postprandial TG incremental area under the curve, so that the ApoB/AI, LDL-C/HDL-C and Non-HDL-C/HDL-C ratio were kept stable. We propose that the following data could represent a dietary fatty acid range of an healthy nutrition for the general population: within a range of total caloric intake of 2,000-2,500 kcal, an oleic acid intake limited to 11 to 16% of TE (28 g/day to 44 g/day), a linoleic acid intake of 4 to 6% of TE (9 g/day to 13 g/day ), and an alpha-linolenic acid intake in sn2 position of 1% of TE (1.5 g/day to 3 g/day), the resilience for the OL/LA/ALA ratio could be expressed by: 11-16/4-6/1. Mots-clés : nutrition, acides gras insaturés : oléique, linoléique, alphalinolénique, réponse postprandiale, paramètres d'athérothrombose.
Sandker et al. [12], sur deux groupes d'hommes âgés, issus des cohortes crétoises (Seven Countries Study) et hollandaises (Zutphen Study), a permis de faire émerger l'intérêt de ce marqueur biologique. En moyenne, le pourcentage de 18:3n-3 mesuré dans les EC plasmatiques des Crétois était significativement plus élevé comparé à celui des Hollandais (0,9 % vs 0,32 % des acides gras), dont la cohorte présentait un taux de mortalité coronarienne 5 fois plus grand que celui de la cohorte crétoise. En outre, l'étude cas-témoins de Simon et al.[10] a montré en 1995 qu'un taux plasmatique de 18:3n-3 élevé était associé à une réduction de 37 % du risque d'accident vasculaire cérébral. Après analyse multivariée pour prendre en compte les facteurs de confusion, susceptibles d'interférer dans le risque étudié, seul le pourcentage de 18:3n-3 dans les EC plasmatiques restait inversement associé au risque d'accident vasculaire cérébral (p < 0,05). De même, l'étude d'intervention de Bemelmans et al. [13], destinée à la prévention MCV chez des sujets à risques, a récemment montré que le pourcentage de 18:3n-3 dans les EC du plasma était inversement associé à la pression diastolique (p < 0,05). Il ressort de l'ensemble de ces données que le niveau d'acide alphalinolénique souhaitable dans les EC du plasma se situerait entre 0,4 et 0,9 % par rapport aux acides gras totaux liés au cholestérol.Article disponible sur le site http://www.ocl-journal.org ou http://dx
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