Bourre J M
Membre de l'Academie de Medecine, INSERM Neuro-pharmaco-nutrition, Hopital Fernand Widal, 200 rue du Faubourg Saint Denis, 75745 Paris cedex 10.
J Nutr Health Aging. 2005 Jul-Aug;9(4):232-42.
Omega-3 polyunsaturated fatty acids have two major field of interest. The first lies in their quantitative abundance and their role in the development and maintenance of the brain. The second is their role in the prevention of different pathologies, mainly the cardiovascular diseases, and more lately some psychiatric disorders, from stress to depression and dementia. Thus, dietary omega-3 fatty acids are very important to ensure brain structure and function, more specifically during development and aging. However, concerning essential alpha-linolenic acid (ALA), most occidental diets contain about 50 % of the recommended dietary allowances. The problem is to know which foods are naturally rich in this fatty acid, and to determine the true impact of the formulations (enriched in omega-3 fatty acids, either ALA or EPA and DHA) in chows used on farms and breeding centres on the nutritional value of the products (meat, butter, milk and dairy products, cheese, and eggs, etc), and thus their effect on the health of consumers, especially to ensure adequate quantities in the diet of the aging people. The consequences (qualitative and quantitative) of modifications in the composition of animal foods on the value of derived products consumed by humans are more marked when single-stomach animals are concerned than multi-stomach animals. Because, for example, hydrogenating intestinal bacteria of the latter group transform a large proportion of polyunsaturated fatty acids in their food into saturated fatty acids, among others, thus depriving them of any biological interest. Under the best conditions, by feeding animals with extracts of linseed and rapeseed grains for example, the level of ALA acid is increased approximately two-fold in beef and six-fold in pork, ten-fold in chicken, and forty-fold in eggs. By feeding animals with fish extracts or algae (oils) the level of DHA is increased about 2-fold in beef, 7-fold in chicken, 6-fold in eggs, and 20-fold in fish (salmon). To obtain such results, it is sufficient to respect only the physiological needs of the animal, which was generally the case with traditional methods. It is important to stress the role of fish, whose nutritional value for humans in terms of lipids (determined by omega-3 fatty acid levels) can vary considerably according to the type of fats the animals have been fed. The aim of preventing some aspects of cardiovascular disease (and other pathologies) can be achieved, or on the contrary frustrated, depending on the nature of fatty acids present in fish flesh, the direct consequence of the nature of fats with which they have been fed. It is the same for eggs, "omega- 3 eggs" being in fact similar to natural eggs, were used in the formulation of certain formula milks for infants, whose composition was closest to that of breast milk. In fact, the additional cost on the price paid by the consumer is modest compared to the considerable gain in nutritional value in terms of omega-3 fatty acids content. Interestingly, in aged people, ALA recommendations in France are increased (0.8% daily energy intake in adult, 0.9 % in aged) and DHA is multiplied by 2 (0.05 % daily energy intake in adult, 0.1 % in aged; as well as in pregnant and lactating women).
ω-3多不饱和脂肪酸有两个主要的研究领域。第一个在于它们的含量丰富以及在大脑发育和维持过程中的作用。第二个是它们在预防不同疾病方面的作用，主要是心血管疾病，最近还包括一些精神疾病，从压力到抑郁和痴呆。因此，膳食中的ω-3脂肪酸对于确保大脑结构和功能非常重要，特别是在发育和衰老过程中。然而，关于必需的α-亚麻酸（ALA），大多数西方饮食中所含的量约为推荐膳食摄入量的50%。问题在于要知道哪些食物天然富含这种脂肪酸，并确定农场和繁育中心使用的饲料（富含ω-3脂肪酸，无论是ALA还是EPA和DHA）对产品（肉类、黄油、牛奶及奶制品、奶酪和鸡蛋等）营养价值的真正影响，进而了解其对消费者健康的影响，尤其是要确保老年人饮食中有足够的量。当涉及单胃动物时，动物食品成分变化对人类食用的衍生产品价值的影响（质量和数量方面）比多胃动物更为显著。因为，例如，后一组动物的肠道氢化细菌会将其食物中的大部分多不饱和脂肪酸转化为饱和脂肪酸等，从而使其失去任何生物学意义。在最佳条件下，例如用亚麻籽和油菜籽提取物喂养动物，牛肉中ALA酸的含量可增加约两倍，猪肉中增加六倍，鸡肉中增加十倍，鸡蛋中增加四十倍。用鱼类提取物或藻类（油）喂养动物，牛肉中DHA的含量可增加约两倍，鸡肉中增加七倍，鸡蛋中增加六倍，鱼类（三文鱼）中增加二十倍。要获得这样的结果，只需满足动物生理需求即可，传统方法通常就是如此。必须强调鱼类的作用，其对人类的营养价值（由ω-3脂肪酸水平决定）会因喂养动物的脂肪类型而有很大差异。预防心血管疾病（及其他疾病）某些方面的目标能否实现，反之是否会受挫，取决于鱼肉中脂肪酸的性质，而这直接取决于喂养它们的脂肪性质。鸡蛋也是如此，“ω-3鸡蛋”实际上与天然鸡蛋类似，被用于某些婴儿配方奶粉的配方中，其成分最接近母乳。事实上，与ω-3脂肪酸含量方面的营养价值大幅提升相比，消费者支付的额外价格并不高。有趣的是，在法国，老年人对ALA的推荐摄入量有所增加（成年人每日能量摄入量的0.8%，老年人为0.9%），DHA则翻倍（成年人每日能量摄入量的0.05%，老年人为0.1%；孕妇和哺乳期妇女也是如此）。
