J'ai trouvé des trucs intéressants:
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Short-term supplementation of low-dose gamma-linolenic acid (GLA), alpha-linolenic acid (ALA), or GLA plus ALA does not augment LCP omega 3 status of Dutch vegans to an appreciable extent.
Fokkema MR, Brouwer DA, Hasperhoven MB, Martini IA, Muskiet FA.
Department of Pathology and Laboratory Medicine, Groningen University Hospital, Groningen, The Netherlands.
m.r.fokkema@path.azg.nl
Vegans do not consume meat and fish and have therefore low intakes of long chain polyunsaturated fatty acids (LCP). They may consequently have little negative feedback inhibition from dietary LCP on conversion of alpha -linolenic acid (ALA) to the LCP omega 3 eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids. We investigated whether supplementation of nine apparently healthy vegans with 2.01 g ALA (4 ml linseed oil), 1.17 g gamma-linolenic acid (GLA) (6 ml borage oil) or their combination increases the LCP omega 3 contents of erythrocytes (RBC) and platelets (PLT), and of plasma phospholipids (PL), cholesterol esters (CE) and triglycerides (TG). The supplements changed the dietary LA/ALA ratio (in g/g) from about 13.7 (baseline) to 6.8 (linseed oil), 14.3 (borage oil) and 6.4 (linseed + borage oil), respectively. ALA or GLA given as single supplements did not increase LCP omega 3 status, but their combination augmented LCP omega 3 (in CE) and EPA (in fasting TG) to a statistically significant, but nevertheless negligible, extent. We conclude that negative feedback inhibition by dietary LCP, if any, does not play an important role in the inability to augment notably DHA status by dietary ALA. The reach of a DHA plateau already at low dietary ALA intakes suggests that dietary DHA causes a non-functional DHA surplus, or is, alternatively, important for maintaining DHA status at a functionally relevant level. Copyright 2000 Harcourt Publishers Ltd.
PMID: 11090255 [PubMed - indexed for MEDLINE]
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Alpha-linolenic acid in rapeseed oil partly compensates for the effect of fish restriction on plasma long chain n-3 fatty acids.
Valsta LM, Salminen I, Aro A, Mutanen M.
Department of Nutrition, National Public Health Institute, Helsinki, Finland.
OBJECTIVE: To examine the ability of alpha-linolenic acid (ALA) in low erucic acid rapeseed oil (RO) to compensate for the effects of a restriction in fish intake on plasma fatty acid composition. DESIGN AND SUBJECTS: Two times 6 weeks' randomized dietary intervention was used with blind crossover design in 40 healthy unconfined women and men (age 20-46y). INTERVENTIONS: Subjects were assigned to two fish restricted diets, namely RO diet and Trisun-sunflower oil (TSO) diet, with similar proportions of saturated : monounsaturated : polyunsaturated fatty acids (11.5:17.5:8.5% of total energy, En%), but differing in their ALA content (2.2 and 0.3 En%) and n-6 : n-3-ratio (3 : 1 and 23 : 1, respectively). The fatty acid compositions of plasma triglycerides (TG), cholesterol esters (CE), and phospholipids (PL) were analyzed by gas chromatography. Dietary intake was evaluated based on 3- to 7-day food records. RESULTS: The proportion of TG and CE ALA decreased on the TSO diet (from 1.6% to 0.9% and from 0.9% to 0.4%, respectively, P < 0.001) and increased on the RO diet (from 1.7% to 3.4% and from 0.9% to 1.3%, respectively, P < 0.001) compared to the baseline level. The proportion of eicosapentaenoic acid (EPA) in all three plasma fractions decreased on the TSO diet but not on the RO diet. The proportions of docosa-hexaenoic acid (DHA) decreased on both experimental diets and there was no difference in CE DHA between the diets. PL docosa-pentaenoic acid (DPA) and PL DHA remained at a higher level on the RO diet compared to the TSO diet (P < 0.001 and P < 0.05, respectively). CONCLUSIONS: ALA is metabolized to EPA in humans to a significant extent. The degree to which rapeseed oil (ca 50g/day) affects the proportion of EPA resembled the effect of a weekly portion (50-100g) of fatty fish depending on the fat content of the fish.
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Achieving optimal essential fatty acid status in vegetarians: current knowledge and practical implications.
Davis BC, Kris-Etherton PM.
Department of Nutritional Sciences, Pennsylvania State University, University Park, PA 16802, USA.
pmk3@psu.edu
...Achieving optimal essential fatty acid status in vegetarians
There are 2 important steps vegetarians can take to improve their EFA status. 1) Maximize the conversion of ALA to EPA and DHA. 2) Provide a direct source of EPA and DHA.
For those with increased needs for EPA and DHA (eg, pregnant and lactating women) or at greater risk for poor conversion (persons with diabetes, those with neurological disorders, premature infants, the elderly), it may be prudent to ensure that there is a direct source of EPA and DHA. While it is not common, it is possible to overconsume n-3 fatty acids. If a person minimizes n-6 fatty acids and uses large amounts of n-3 fatty acids [ie, > 2 tbsp (28 g) flax oil/d], resulting in an n-6-to-n-3 ratio of < 1:1, insufficient LA conversion to AA can occur. Elongase and desaturase enzymes preferentially convert n-3 fatty acids, when compared with n-6 fatty acids. A balance of 2:1–4:1 (n-6:n-3) appears optimal for vegetarians and others who do not receive preformed EPA and DHA.
Maximizing conversion of n-3 fatty acids
While conversion of EFAs to longer-chain fatty acids is, at least in part, dependent on genetics, age, and overall health, several dietary factors also have a significant impact on the conversion process. First, it is important to ensure that the diet is nutritionally adequate, as poorly designed diets can impair the conversion process. Insufficient energy or protein decreases the activity of conversion enzymes, as can deficiencies of pyridoxine, biotin, calcium, copper, magnesium, and zinc (56, 57). Excessive intakes of trans fatty acids can also depress conversion enzymes. In addition, alcohol inhibits the activity of {Delta}-5 and {Delta}-6 desaturase and depletes tissues of long-chain n-3 fatty acids (58). High n-6 fatty acid content can have a profound effect on n-3 fatty acid conversion, reducing it as much as 40% (59).
In the context of current guidelines, total polyunsaturated fatty acid intake should be < 7% of calories, with 10% being the maximum. Vegetarians currently consume about 8–12% of their calories from polyunsaturated fatty acid. Given a total polyunsaturated fatty acid intake of 7–10% of calories, to achieve an n-6-to-n-3 ratio of 4:1, < 1.5–2% of calories should be obtained from n-3 fatty acids and, as a result, 5.5–8% of calories from n-6 fatty acids. Alternatively, LA can be decreased; however, given the recognized health benefits of LA, a marked reduction is not recommended. To achieve reduced n-6 intakes, oils rich in n-6 fatty acids should not be used as primary cooking oils. Cooking oils with the greatest n-6 fatty acid content include safflower oil (75% n-6), grapeseed oil (70% n-6), sunflower oil (65% n-6), corn oil (57% n-6), cottonseed oil (52% n-6), and soybean oil (51% n-6). Processed foods, convenience foods, and snack foods also are significant contributors to n-6 intake; thus, their use should be moderate. n-6-Rich whole foods such as sunflower seeds, pumpkin seeds, sesame seeds, walnuts, wheat germ, and soy foods need not be avoided, as they tend to be relatively minor contributors to overall n-6 intake. These foods also provide a myriad of beneficial dietary components, including phytochemicals, fiber, B vitamins, vitamin E, and trace minerals.
The primary fat in the diet should come from foods and oils rich in monounsaturated fat. When monounsaturated fats predominate, saturated fats, trans fatty acids, and n-6 fatty acids are kept in check and the ratio of n-6 to n-3 fatty acids improves. Monounsaturated fats are high in nuts (except for walnuts and butternuts), peanuts (a legume), olive oil, olives, avocados, canola oil, high-oleic sunflower oil, and high-oleic safflower oil. Whole foods rather than oils are better sources of monounsaturated fats because they contribute many other nutrients to the diet.
Finally, it is important to ensure that there are sufficient amounts of ALA, which is necessary for the production of EPA and DHA. Most healthy vegetarians would be well advised to double their intake of ALA, providing >= 1% of energy from n-3 fatty acids or 1.1 g/1000 cal. For those with increased needs or decreased capacity to convert, an intake of 2% of energy or 2.2 g/1000 cal may be necessary. The primary sources of ALA are selected seeds, nuts, and legumes (flaxseed, hempseed, canola, walnuts, and soy) and the green leaves of plants, including phytoplankton and algae. Table 1 provides a list of common ALA-rich plant foods, the percentage of fat as ALA, the n-6-to-n-3 ratio, and the total grams of ALA per serving...
Texte complet:
ça laisse songeur...
Il semblerait qu'il ressort de ces extraits 2 trucs:
1/ concurrence entre omega 3/6
2/lorsque le corps atteint un niveau fonctionnel suffisant d'EPA/DHA, et aussi bas soit-il, un apport supplémentaire en ALA ne semble pas augmenter le taux d'omega 3 à l'inverse des apports directes de DHA/EPA (huiles de poissons), donc la conversion des ALA en DHA/EPA...semblerait avoir un seuil limite au dessus duquel la conversion ne se fait plus quelquesoit l'apport en ALA...ce seuil est il suffisant pour maintenir un état de santé optimal??
A+
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