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  1. #1
    Usuari@ expert@ Avatar de sujal
    Fecha de ingreso
    marzo-2006
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    Guadalajara
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    8.690

    Conversión ALA - DHA


    ¿No es necesario suplementar?

    Cita Iniciado por flex23
    Sobre el DHA podemos obtenerlo con una adecuada ingesta de ácido linolénico (ALA) que lo encontramos en:

    - aceite de linaza
    - aceite de sacha inchi (bueno esto hay enPerú no se si hay por allá)
    - nueces
    - alimentos de soya (excepto aceite de soya por su contribución en omega 6, es decir, leche de soya, carne de soya y tofu)
    - plantas de hoja verde incluyendo algas.

    El DHA se convierte a partir de ALA y el EPA también. Entre el 5 a 10% de ALA lo convertimos en EPA y entre el 2 a 5% de ALA lo convertimos a DHA. Aquí algunas fuentes de esto:

    8. Ghafoorunissa SA. Requirements of dietary fats to meet nutritional
    needs and prevent the risk of atherosclerosis—an Indian perspective.
    Indian J Med Res 1998;108:191–202.

    9. Emken EA, Adolf RO, Gulley RM. Dietary linoleic acid influences
    desaturation and acylation of deuterium-labeled linoleic and linolenic
    acids in young adult males. Biochim Biophys Acta 1994;1213:
    277–88.

    10. Gerster H. Can adults adequately convert _-linolenic acid (18:3 n_3)
    to eicosapentaenoic acid (20:5 n_3) and docosahexaenoic acid (22:
    6 n_3)? Int J Vitam Nutr Res 1998;68:159–73.

    Can adults adequately convert alpha-linolenic acid (18:3n-3) to eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3)?Gerster H.(1998)
    Vitamin Research Department, F. Hoffman-Roche Ltd, Basel, Switzerland.

    A diet including 2-3 portions of fatty fish per week, which corresponds to the intake of 1.25 g EPA (20:5n-3) + DHA (22:6n-3) per day, has been officially recommended on the basis of epidemiological findings showing a beneficial role of these n-3 long-chain PUFA in the prevention of cardiovascular and inflammatory diseases. The parent fatty acid ALA (18:3n-3), found in vegetable oils such as flaxseed or rapeseed oil, is used by the human organism partly as a source of energy, partly as a precursor of the metabolites, but the degree of conversion appears to be unreliable and restricted. More specifically, most studies in humans have shown that whereas a certain, though restricted, conversion of high doses of ALA to EPA occurs, conversion to DHA is severely restricted. The use of ALA labelled with radioisotopes suggested that with a background diet high in saturated fat conversion to long-chain metabolites is approximately 6% for EPA and 3.8% for DHA. With a diet rich in n-6 PUFA, conversion is reduced by 40 to 50%. It is thus reasonable to observe an n-6/n-3 PUFA ratio not exceeding 4-6. Restricted conversion to DHA may be critical since evidence has been increasing that this long-chain metabolite has an autonomous function, e.g. in the brain, retina and spermatozoa where it is the most prominent fatty acid. In neonates deficiency is associated with visual impairment, abnormalities in the electroretinogram and delayed cognitive development. In adults the potential role of DHA in neurological function still needs to be investigated in depth. Regarding cardiovascular risk factors DHA has been shown to reduce triglyceride concentrations. These findings indicate that future attention will have to focus on the adequate provision of DHA which can reliably be achieved only with the supply of the preformed long-chain metabolite.

    PMID: 9637947 [PubMed - indexed for MEDLINE]
    De esta forma por ejemplo podemos obtener 100 miligramos de DHA consumiendo 100 x 20 mg de ALA (2000 mg), lo cual equivale a 2 gramos de ALA (considerando la conversión más baja). Y en el peor de los casos si la conversión es de 2% pues sería 100x 50 lo cual es 5 g de ALA (5000 mg). Y para obtener de 2 a 5 gr de ALA tenemos de sobra si consumimos, aceite de linaza, harina de linaza, aceite de sacha inchi, nueces, soya, etc.

    Las recomendaciones para obtener niveles óptimos de DHA son variadas (Fuente: Achieving optimal essential fatty acid status in vegetarians: current knowledge and practical implications
    Am J Clin Nutr 2003;78(suppl):640S–6S. )
    :

    1) Consumir una gran variedad de alimentos vegetales, el fundamento de la dieta
    2) Obtener la mayor cantidad de grasa de alimentos enteros: nueces, semillas, aceite de oliva, palta o aguacate y alimentos de soya.
    3) Si se usan grasas y aceites concentrasos seleccionar aquellos ricos en grasas monoinsaturadas como: aceite de oliva, de canola o de nuez. Se recomienda un uso moderado de aceites con omega 6 (aceite de girasol, aceite de soya, entre otros).
    4) Limitar la ingesta de alimentos procesados, y alimentos extra-fritos que son ricos en ácidos grasos trans y omega 6.
    5) Reducir la ingesta de alimentos ricos en grasa saturada y colesterol.
    6) Incluir alimentos ricos en ácidos grasos omega 3 en la dieta diaria. Tratar de consumir de 2 a 4 gramos de ALA/día (esto se logra por ejemplo consumiendo unos 6 ml de aceite de linaza, asumiendo hipotéticamente que sea la única y exclusiva fuente diaria que consumimos, considerando que hay más fuentes como nueces, soya,etc no tiene por qué ser así.)
    7) Considera usar una fuente de DHA (100-300 mg/d)

    Al ultimo menciona lo de consumir suplementos de DHA pero eso es algo opcional y si mantenemos una ingesta adecuada de ALA la conversión será suficiente. Y más aún si seguimos las 5 primeras recomendaciones (en una dieta vegana no hay colesterol así que en el punto 5 sale sobrando).

    Saludos
    A pesar de tener la ingesta significativamente más baja de EPA y DHA (asociado con el consumo de pescado), los niveles de EPA y DHA en los vegetarianos y los veganos fueron aproximadamente los mismos que los de quienes comen pescado regularmente, según los resultados publicados en la revista American Journal of Clinical Nutrition.

    Los resultados indican que cuando las personas no consumen los niveles adecuados de EPA y DHA, al igual que los veganos y vegetarianos no comen pescado, sus cuerpos responden aumentando los niveles de conversión de ALA a EPA.

    Dietary intake and status of n-3 polyunsaturated fatty acids in a population of fish-eating and non-fish-eating meat-eaters, vegetarians, and vegans and the precursor-product ratio of α-linolenic acid to long-chain n-3 polyunsaturated fatty acids: results from the EPIC-Norfolk cohort.
    Welch AA, Shakya-Shrestha S, Lentjes MA, Wareham NJ, Khaw KT. (2010)


    CONCLUSIONS: Substantial differences in intakes and in sources of n-3 PUFAs existed between the dietary-habit groups, but the differences in status were smaller than expected, possibly because the precursor-product ratio was greater in non-fish-eaters than in fish-eaters, potentially indicating increased estimated conversion of ALA. If intervention studies were to confirm these findings, it could have implications for fish requirements.

    Nuevo estudio sobre DHA

  2. #2
    Usuari@ expert@ Avatar de sujal
    Fecha de ingreso
    marzo-2006
    Ubicación
    Guadalajara
    Mensajes
    8.690
    ¿Sí es necesario suplementar?


    2002: Burdge Graham C; Jones Amanda E; Wootton Stephen A

    Eicosapentaenoic and docosapentaenoic acids are the principal products of alpha-linolenic acid metabolism in young men*.

    The British journal of nutrition 2002;88(4):355-63.

    The capacity for conversion of alpha-linolenic acid (ALNA) to n-3 long-chain polyunsaturated fatty acids was investigated in young men. Emulsified [U-13C]ALNA was administered orally with a mixed meal to six subjects consuming their habitual diet. Approximately 33 % of administered [13C]ALNA was recovered as 13CO2 on breath over the first 24 h. [13C]ALNA was mobilised from enterocytes primarily as chylomicron triacylglycerol (TAG), while [13C]ALNA incorporation into plasma phosphatidylcholine (PC) occurred later, probably by the liver. The time scale of conversion of [13C]ALNA to eicosapentaenoic acid (EPA) and docosapentaenoic acid (DPA) suggested that the liver was the principal site of ALNA desaturation and elongation, although there was some indication of EPA and DPA synthesis by enterocytes. [13C]EPA and [13C]DPA concentrations were greater in plasma PC than TAG, and were present in the circulation for up to 7 and 14 d, respectively. There was no apparent 13C enrichment of docosahexaenoic acid (DHA) in plasma PC, TAG or non-esterified fatty acids at any time point measured up to 21 d. This pattern of 13C n-3 fatty acid labelling suggests inhibition or restriction of DHA synthesis downstream of DPA. [13C]ALNA, [13C]EPA and [13C]DPA were incorporated into erythrocyte PC, but not phosphatidylethanolamine, suggesting uptake of intact plasma PC molecules from lipoproteins into erythrocyte membranes. Since the capacity of adult males to convert ALNA to DHA was either very low or absent, uptake of pre-formed DHA from the diet may be critical for maintaining adequate membrane DHA concentrations in these individuals.

    Williams, C. M. and G. Burdge (2006). "Long-chain n-3 PUFA: plant v. marine sources." Proc Nutr Soc 65(1): 42-50.

    Increasing recognition of the importance of the long-chain n-3 PUFA, EPA and DHA, to cardiovascular health, and in the case of DHA to normal neurological development in the fetus and the newborn, has focused greater attention on the dietary supply of these fatty acids. The reason for low intakes of EPA and DHA in most developed countries (0.1-0.5 g/d) is the low consumption of oily fish, the richest dietary source of these fatty acids. An important question is whether dietary intake of the precursor n-3 fatty acid, alpha-linolenic acid (alphaLNA), can provide sufficient amounts of tissue EPA and DHA by conversion through the n-3 PUFA elongation-desaturation pathway. alphaLNA is present in marked amounts in plant sources, including green leafy vegetables and commonly-consumed oils such as rape-seed and soyabean oils, so that increased intake of this fatty acid would be easier to achieve than via increased fish consumption. However, alphaLNA-feeding studies and stable-isotope studies using alphaLNA, which have addressed the question of bioconversion of alphaLNA to EPA and DHA, have concluded that in adult men conversion to EPA is limited (approximately 8%) and conversion to DHA is extremely low (<0.1%). In women fractional conversion to DHA appears to be greater (9%), which may partly be a result of a lower rate of utilisation of alphaLNA for beta-oxidation in women. However, up-regulation of the conversion of EPA to DHA has also been suggested, as a result of the actions of oestrogen on Delta6-desaturase, and may be of particular importance in maintaining adequate provision of DHA in pregnancy. The effect of oestrogen on DHA concentration in pregnant and lactating women awaits confirmation.
    Conversion of α-linolenic acid to longer-chain polyunsaturated fatty acids in human adults
    Graham C. BURDGE*, Philip C. CALDER (2005)

    Institute of Human Nutrition, University of Southampton, Southampton, UK

    CONCLUSIONS
    Studies using chronically increased αLNA intake or using a single bolus of isotopically-labelled αLNA yield the same conclusion: that conversion of αLNA to longer-chain PUFA, particularly DHA, in humans appears to be limited. However, there are important differences between men and women in capacity for synthesis of EPA and DHA from αLNA and this may be affected by physiological state (e.g., pregnancy).
    If demands for EPA and DHA are modest and primarily serve to support membrane turnover and renewal in adults, then it is possible that in healthy individuals consuming a balanced diet limited capacity for synthesis of EPA and DHA may be sufficient to maintain tissue function. However, in situations where demand for long chain n-3 PUFA, especially DHA, is increased (e.g., during pregnancy and lactation), then synthesis from αLNA may be insufficient to meet the demand, although there may be physiological mechanisms by which αLNA conversion is up-regulated. Clearly more research in this area is required before firmer conclusions can be drawn.

  3. #3
    Banned
    Fecha de ingreso
    diciembre-2008
    Ubicación
    Madrid
    Mensajes
    36
    Me hacéis la cabeza un lío.

  4. #4
    Usuari@ expert@ Avatar de sujal
    Fecha de ingreso
    marzo-2006
    Ubicación
    Guadalajara
    Mensajes
    8.690
    Lo siento Lluís, pero es lo que hay hasta la fecha. Es posible que en posteriores estudios se descubra que no hay problemas de conversión cuando se trata de un vegano feliz porque las endorfinas... tal y tal. Por poner un ejemplo sin fundamento.

    Ahora mismo y por las fechas de las publicaciones habría que suplementar. Ahora bien, si alguien dispone de estudios más actualizados sobre correctas conversiones (las de Flex23 ya están un poco anticuadas), que las comparta!

  5. #5
    Usuari@ expert@ Avatar de sujal
    Fecha de ingreso
    marzo-2006
    Ubicación
    Guadalajara
    Mensajes
    8.690
    Very low n-3 long-chain polyunsaturated fatty acid status in Austrian vegetarians and vegans.
    Kornsteiner M, Singer I, Elmadfa I.
    Department of Nutritional Sciences, Faculty of Life Sciences, University of Vienna, Vienna, Austria.

    BACKGROUND/AIMS: The objective of the study was to collect data on dietary fat intake of omnivores, vegetarians, vegans and semi-omnivores as well as its impact on n-3 and n-6 fatty acids in long-term markers such as sphingolipids, phosphatidylcholine (PC), phosphatidylserine (PS), phosphatidylethanolamine (PE) as well as the calculated sphingo- and phospholipids (SPL) of erythrocytes.

    METHOD: The present observational study included 98 Austrian adult volunteers of both genders, of which 23 were omnivores, 25 vegetarians, 37 vegans, and 13 semi-omnivores. Information on anthropometry using measured body weight and height was obtained. The amount and composition of ingested fat were calculated from 24-hour recalls and the fatty acid pattern in the phospholipids was assessed using gas chromatography.

    RESULTS: The unbalanced n-6/n-3 ratio and the limited dietary sources of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in vegans and vegetarians led to reductions in C20:5n-3, C22:5n-3, C22:6n-3 and total n-3 fatty acids in SPL, PC, PS and PE compared with omnivores and semi-omnivores. The total content of polyunsaturated fatty acids, monounsaturated fatty acids and saturated fatty acids remained unchanged.

    CONCLUSION: The vegetarian diet, with an average n-6/n-3 ratio of 10/1, promotes biochemical n-3 tissue decline. To ensure physical, mental and neurological health vegetarians have to reduce the n-6/n-3 ratio with an additional intake of direct sources of EPA and DHA, regardless of age and gender. (c) 2008 S. Karger AG, Basel.

    PMID: 18305382 [PubMed - indexed for MEDLINE]

    http://www.ncbi.nlm.nih.gov/pubmed/1...ubmed_RVDocSum

    Conclusión: La dieta vegetariana, con una media n-6/n-3 relación de 10/1, promueve el declive de la bioquímica ¿¿¿? de n-3. Para garantizar la integridad física, salud mental y neurológica vegetarianos tienen que reducir el ratio de n-6/n-3 con una ingesta adicional de fuentes directas de EPA y DHA, independientemente de la edad y el sexo.

  6. #6
    Usuari@ expert@ Avatar de sujal
    Fecha de ingreso
    marzo-2006
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    Guadalajara
    Mensajes
    8.690
    A continuación otro estudio en la línea de no suplementar:


    Long-chain n-3 polyunsaturated fatty acids in plasma in British meat-eating, vegetarian, and vegan men.(2005)

    Rosell MS, Lloyd-Wright Z, Appleby PN, Sanders TA, Allen NE, Key TJ.
    Cancer Research UK Epidemiology Unit, University of Oxford, Oxford, United Kingdom.

    BACKGROUND: Plasma concentrations of long-chain n-3 polyunsaturated fatty acids are lower in vegetarians and in vegans than in omnivores. No data are available on whether these concentrations differ between long- and short-term vegetarians and vegans.

    OBJECTIVES: We compared plasma fatty acid composition in meat-eaters, vegetarians, and vegans and examined whether the proportions of eicosapentaenoic acid (20:5n-3; EPA), docosapentaenoic acid (22:5n-3; DPA), and docosahexaenoic acid (22:6n-3; DHA) were related to the subjects' duration of adherence to their diets or to the proportions of plasma linoleic acid (18:2n-6; LA) and alpha-linolenic acid (18:3n-3; ALA).

    DESIGN: The present cross-sectional study included 196 meat-eating, 231 vegetarian, and 232 vegan men in the United Kingdom. Information on anthropometry, diet, and smoking habits was obtained through a questionnaire. Total fatty acid composition in plasma was measured.

    RESULTS: The proportions of plasma EPA and DHA were lower in the vegetarians and in the vegans than in the meat-eaters, whereas only small differences were seen for DPA. Plasma EPA, DPA, and DHA proportions were not significantly associated with the duration of time since the subjects became vegetarian or vegan, which ranged from <1 y to >20 y. In the vegetarians and the vegans, plasma DHA was inversely correlated with plasma LA.

    CONCLUSIONS: The proportions of plasma long-chain n-3 fatty acids were not significantly affected by the duration of adherence to a vegetarian or vegan diet. This finding suggests that when animal foods are wholly excluded from the diet, the endogenous production of EPA and DHA results in low but stable plasma concentrations of these fatty acids.

    PMID: 16087975 [PubMed - indexed for MEDLINE]
    http://www.ncbi.nlm.nih.gov/pubmed/1...ubmed_RVDocSum

    RESULTADOS: La proporción de EPA y DHA en plasma fueron más bajos en los vegetarianos y veganos en el que en el comen carne, mientras que sólo se observaron pequeñas diferencias de DPA. Las proporciones de EPA, DPA Y DHA en plasma no se asociaron significativamente con la duración de tiempo desde que adoptaron la dieta vegetariana o vegana, que oscilaban entre <1 y a> 20 a. En los vegetarianos y los veganos, plasma DHA fue inversamente correlacionada con el plasma LA.
    .
    CONCLUSIONES: La proporción de plasma de cadena larga n-3 ácidos grasos no fueron significativamente afectados por la duración de la adhesión a una dieta vegetariana o vegana. Este hallazgo sugiere que cuando los alimentos animales son totalmente excluidos de la dieta, la producción endógena de EPA y DHA dan resultados bajos pero estables de concentraciones plasmáticas de estos ácidos grasos.

  7. #7
    Usuari@ expert@
    Fecha de ingreso
    diciembre-2007
    Mensajes
    3.705
    Pero los omega 3 no son únicamente para la protección cardiovascular, sino que además cumplen muchas otras funciones.

  8. #8
    Usuari@ expert@ Avatar de Kalkoven
    Fecha de ingreso
    diciembre-2006
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    1.861
    Cita Iniciado por VeG Ver mensaje
    Pero los omega 3 no son únicamente para la protección cardiovascular, sino que además cumplen muchas otras funciones.
    Ya, obviamente ése es un estudio, entre muchos otros... (sujal lo ha copiado de aquí: http://www.forovegetariano.org/foro/...&postcount=232)

  9. #9
    Usuari@ expert@ Avatar de sujal
    Fecha de ingreso
    marzo-2006
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    Guadalajara
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    8.690
    Cita Iniciado por Veg
    Pero los omega 3 no son únicamente para la protección cardiovascular, sino que además cumplen muchas otras funciones.
    Abro un hilo aparte para tratar los estudios relacionados con la suplementación de los omega 3 y su incidencia en el sistema cardiovascular.

    Suplementación AG Omega 3 para beneficios cardiovasculares

  10. #10
    Mediocabrón proud member
    Fecha de ingreso
    enero-2009
    Mensajes
    7.760

    Sale otra vez en la revista Vegetus de la UVE este estudio de septiembre de 2009:

    DHA status of vegetarians.

    Sanders TA.

    Nutritional Sciences Division (TABS), King's College London, Franklin-Wilkins Building, 150 Stamford Street, London SE19NH, UK. tom.sanders@kcl.ac.uk

    BACKGROUND: Docosahexaenoic acid (22:6n-3; DHA) is absent from vegan diets and present in limited amounts in vegetarian diets. OBJECTIVE: To review DHA status in vegetarians and vegans. DESIGN: To identify published studies and review their findings. RESULTS: Dietary analyses show that vegan diets are devoid of DHA and vegetarian diets that included dairy food and eggs only provide about 0.02 g DHA/d. Vegetarian and especially vegan diets supply more linoleic acid (18:2n-6) than omnivore diets. The intake of alpha-linolenic acid (18:3n-3) also tends to be similar or greater but depends on culinary oils used. The proportions of DHA in plasma, blood cells, breast milk, and tissues are substantially lower in vegans and vegetarians compared with omnivores. The lower proportions of DHA are accompanied by correspondingly higher proportions of the long-chain derivatives of linoleic acid, indicating that the capacity to synthesize long-chain polyunsaturated fatty acids is not limited. Short-term dietary supplementation with alpha-linolenic acid increases the proportion of eicosapentaenoic acid (20:5n-3) but does not increase the proportion of DHA in blood lipids. Small amounts of preformed DHA (as low as 200mg) result in a large increase in the proportion of DHA in blood lipids in vegetarians and vegans. There is no evidence of adverse effects on health or cognitive function with lower DHA intake in vegetarians. CONCLUSIONS: Preformed DHA in the diet of omnivores explains the relatively higher proportion of this fatty acid in blood and tissue lipids compared with vegetarians. The pathophysiological significance of this difference remains to be determined.
    En ausencia de pruebas convincentes sobre supuestos efectos perjudiciales por falta de DHA en la deita de los vegetarianos, debemos concluir que las necesidades de ácidos grasos omega-3 pueden ser cubiertas con el ALA (ácido alfa-linolénico) dietético elaborado por las plantas.

 

 
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