Les niveaux d'oméga 3 corporels ont chuté au 20ème siècle

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Changes in consumption of omega-3 and omega-6 fatty acids in the United States during the 20th century.
Blasbalg TL Am J Clin Nutr. 2011 May;93(5):950-62.

BACKGROUND:
The consumption of omega-3 (n-3) and omega-6 (n-6) essential fatty acids in Western diets is thought to have changed markedly during the 20th century.

OBJECTIVE:
We sought to quantify changes in the apparent consumption of essential fatty acids in the United States from 1909 to 1999.

DESIGN:
We calculated the estimated per capita consumption of food commodities and availability of essential fatty acids from 373 food commodities by using economic disappearance data for each year from 1909 to 1999. Nutrient compositions for 1909 were modeled by using current foods (1909-C) and foods produced by traditional early 20th century practices (1909-T).

RESULTS:
The estimated per capita consumption of soybean oil increased >1000-fold from 1909 to 1999. The availability of linoleic acid (LA) increased from 2.79% to 7.21% of energy (P < 0.000001), whereas the availability of α-linolenic acid (ALA) increased from 0.39% to 0.72% of energy by using 1909-C modeling. By using 1909-T modeling, LA was 2.23% of energy, and ALA was 0.35% of energy. The ratio of LA to ALA increased from 6.4 in 1909 to 10.0 in 1999. The 1909-T but not the 1909-C data showed substantial declines in dietary availability (percentage of energy) of n-6 arachidonic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Predicted net effects of these dietary changes included declines in tissue n--3 highly unsaturated fatty acid status (36.81%, 1909-T; 31.28%, 1909-C; 22.95%, 1999) and declines in the estimated omega-3 index (8.28, 1909-T; 6.51, 1909-C; 3.84, 1999).

CONCLUSION:
The apparent increased consumption of LA, which was primarily from soybean oil, has likely decreased tissue concentrations of EPA and DHA during the 20th century.

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On sent bien par ce graphique que le mouvement végétarien actuel est tout à fait spontané

Trends in the estimated per capita consumption of major food commodities (A), major fat commodities (B), and vegetable and seed oils (C) between 1909 and 1999. kg/p/y, kilograms per person per year.

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Soybean oil, shortening (primarily hydrogenated soybean and cottonseed oils), and poultry became major sources of calories late in the 20th century. Soybean oil, which accounted for 0.006% of energy in 1909, was the fourth major contributor of food calories in 1999 (7.38% of energy), which was a >1000-fold increase (Table 3). Poultry as a source of calories increased >4-fold from 0.94% of energy in 1909 to 4.94% of energy in 1999.

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Availability of essential fatty acids from 1909 to 1999. Inputs to the equation of Lands et al (2) to estimate US tissue compositions: P6, P3, H6, and H3 indicate linoleic acid (LA), α-linolenic acid (ALA), n−6 highly unsaturated fatty acids (HUFAs), and n−3 HUFAs, respectively. 1909-T data are indicated by solid arrows for LA (2.23% of energy), ALA (0.35% of energy), arachidonic acid (AA) (0.67% of energy), docosahexaenoic acid (DHA) (0.033% of energy), eicosapentaenoic acid (EPA) (0.028% of energy), and docosapentaenoic acid (DPAn−3) (0.018% of energy).

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These data do not support the assertion that the consumption of total n−3 fatty acids has decreased or that the ratio of n−6 to n−3 has markedly increased during the 20th century. With the use of 1909-T data, the dietary availability of n−3 HUFAs and AA decreased compared with the availability in 1999. We estimated that the net effect of these dietary changes, primarily because of changes in the availability of LA, was to lower the n−3 EPA, DPA n−3, and DHA status of human tissues, which were expressed as either the percentage of n−3 in HUFAs or the omega-3 index.

[Nutrimuscle-Conseils]

The majority of the increase in soybean oil consumption occurred in the latter half of the 20th century (1946–1999; Figure 1C). No single cause can be identified for this staggering rise. Rather, the increase was likely attributable to a combination of factors, including the following:
1) the desirable characteristics of soybeans as a crop (27), such as high yields and the nitrogen-fixing capability;
2) the expanded processing techniques for seed oils, such as solvent extraction and partial hydrogenation (28);
3) the increased demand for soybean meal (but not oil) as a preferred protein for the industrial-scale production of livestock and poultry, with excess oil as a byproduct (28–30);
4) the decreased competition from cottonseed oil as synthetic alternatives (eg, polyester) reduced the demand for cotton fiber (30);
5) price-support policies, such as Public Law 480, which decreased the economic risk for US soybean farmers and processors (30);

6) aggressive and successful marketing campaigns by trade groups (31); and

7) recommendations to consume more polyunsaturated oils at the expense of animal fats (32) (Figure 10).

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A high dietary LA consumption may reduce the contents of tissue EPA, DPA n−3, and DHA by the following 3 mechanisms:

1) the impairment of the conversion of ALA (18:3n−3) to 18:4n−3 and EPA (20:5n−3) by competing for the active site of Δ6-desaturase (33),
2) the impairment of the conversion of 24:5n−3–24:6n−3 by competing for the active site of Δ6-desaturase in the endoplasmic reticulum (34, 35), which inhibits the production of DHA (22:6n−3); and
3) the impairment of the incorporation of EPA, DPA n−3, DHA, and n−6 AA into tissue membranes by competing for esterification into the sn-2 position of phospholipids (36).

The competition of LA with n−3 and n−6 HUFAs for phospholipid incorporation may account for the significant inverse correlation of LA with EPA (r = −0.46, P < 0.01), DHA (r = −0.49, P < 0.01), and AA (r = −0.60, P < 0.01) shown in erythrocyte phosphatidylcholine of pregnant Canadians as reported by Friesen and Innis (36). In the Los Angeles Veterans Study, a very high–LA diet (15% of energy) reduced AA concentrations by 40% (P < 0.05) in coronary atheroma phospholipids (37), presumably via the same mechanism. Thus, high dietary intakes of LA may displace AA in tissues, which may account for the potential benefits of LA at very high intakes. However, because LA may also displace EPA and DHA, net effects may be nonlinear and difficult to predict.

[Nutrimuscle-Diététique]

Changements dans la consommation d'acides gras oméga-3 et oméga-6 aux États-Unis au cours du 20e siècle.
Blasbalg TL Am J Clin Nutr. Mai 2011; 93 (5): 950-62.

CONTEXTE:
On pense que la consommation d'acides gras essentiels oméga-3 (n-3) et oméga-6 (n-6) dans les régimes alimentaires occidentaux a considérablement changé au cours du XXe siècle.

OBJECTIF:
Nous avons cherché à quantifier les changements dans la consommation apparente d'acides gras essentiels aux États-Unis de 1909 à 1999.

CONCEPTION:
Nous avons calculé la consommation estimée par habitant de produits alimentaires et la disponibilité des acides gras essentiels de 373 produits alimentaires en utilisant les données de disparition économique pour chaque année de 1909 à 1999. Les compositions des nutriments pour 1909 ont été modélisées en utilisant les aliments actuels (1909-C) et les aliments produit par les pratiques traditionnelles du début du XXe siècle (1909-T).

RÉSULTATS:
La consommation estimée d'huile de soja par habitant a augmenté> 1 000 de 1909 à 1999. La disponibilité de l'acide linoléique (AL) est passée de 2,79% à 7,21% d'énergie (P <0,000001), tandis que la disponibilité de l'acide α-linolénique ( ALA) est passé de 0,39% à 0,72% d'énergie en utilisant la modélisation 1909-C. En utilisant la modélisation 1909-T, LA était de 2,23% d'énergie et l'ALA de 0,35% d'énergie. Le rapport LA / ALA est passé de 6,4 en 1909 à 10,0 en 1999. Les données de 1909-T mais pas celles de 1909-C ont montré une baisse substantielle de la disponibilité alimentaire (pourcentage d'énergie) de l'acide arachidonique n-6, l'acide eicosapentaénoïque (EPA) et l'acide docosahexaénoïque (DHA). Les effets nets prévus de ces changements alimentaires comprenaient une baisse de l'état des acides gras hautement insaturés n - 3 dans les tissus (36,81%, 1909-T; 31,28%, 1909-C; 22,95%, 1999) et une baisse de l'indice d'oméga-3 estimé ( 8.28, 1909-T; 6.51, 1909-C; 3.84, 1999).

CONCLUSION:
L'augmentation apparente de la consommation de LA, qui provenait principalement de l'huile de soja, a probablement diminué les concentrations tissulaires d'EPA et de DHA au cours du 20e siècle.

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Une consommation alimentaire élevée de LA peut réduire le contenu des tissus EPA, DPA n-3 et DHA par les 3 mécanismes suivants:

1) la dégradation de la conversion de l'ALA (18: 3n-3) en 18: 4n-3 et de l'EPA (20: 5n-3) en rivalisant pour le site actif de la Δ6-désaturase (33),
2) l'altération de la conversion de 24: 5n − 3–24: 6n − 3 en rivalisant pour le site actif de Δ6-désaturase dans le réticulum endoplasmique (34, 35), qui inhibe la production de DHA (22: 6n− 3); et
3) l'altération de l'incorporation d'EPA, de DPA n-3, de DHA et de n-6 AA dans les membranes tissulaires en rivalisant pour l'estérification dans la position sn-2 des phospholipides (36).

La compétition de LA avec n-3 et n-6 HUFA pour l'incorporation de phospholipides peut expliquer la corrélation inverse significative de LA avec EPA (r = −0,46, P <0,01), DHA (r = −0,49, P <0,01), et AA (r = −0,60, P <0,01) indiqués dans la phosphatidylcholine érythrocytaire de Canadiennes enceintes, tel que rapporté par Friesen et Innis (36). Dans la Los Angeles Veterans Study, un régime très riche en LA (15% d'énergie) a réduit les concentrations d'AA de 40% (P <0,05) dans les phospholipides de l'athérome coronaire (37), vraisemblablement via le même mécanisme. Ainsi, des apports alimentaires élevés de LA peuvent déplacer AA dans les tissus, ce qui peut expliquer les avantages potentiels de LA à des apports très élevés. Cependant, étant donné que LA peut également déplacer l'EPA et le DHA, les effets nets peuvent être non linéaires et difficiles à prévoir.