Changes in consumption of omega-3 and omega-6 fatty acids in the United States during the 20th century.

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.

n-6 fatty acid-specific and mixed polyunsaturate dietary interventions have different effects on CHD risk: a meta-analysis of randomised controlled trials.

Randomised controlled trials (RCT) of mixed n-6 and n-3 PUFA diets, and meta-analyses of their CHD outcomes, have been considered decisive evidence in specifically advising consumption of 'at least 5-10 % of energy as n-6 PUFA'. Here we (1) performed an extensive literature search and extracted detailed dietary and outcome data enabling a critical examination of all RCT that increased PUFA and reported relevant CHD outcomes; (2) determined if dietary interventions increased n-6 PUFA with specificity, or increased both n-3 and n-6 PUFA (i.e. mixed n-3/n-6 PUFA diets); (3) compared mixed n-3/n-6 PUFA to n-6 specific PUFA diets on relevant CHD outcomes in meta-analyses; (4) evaluated the potential confounding role of trans-fatty acids (TFA). n-3 PUFA intakes were increased substantially in four of eight datasets, and the n-6 PUFA linoleic acid was raised with specificity in four datasets. n-3 and n-6 PUFA replaced a combination of TFA and SFA in all eight datasets. For non-fatal myocardial infarction (MI)+CHD death, the pooled risk reduction for mixed n-3/n-6 PUFA diets was 22 % (risk ratio (RR) 0.78; 95 % CI 0.65, 0.93) compared to an increased risk of 13 % for n-6 specific PUFA diets (RR 1.13; 95 % CI 0.84, 1.53). Risk of non-fatal MI+CHD death was significantly higher in n-6 specific PUFA diets compared to mixed n-3/n-6 PUFA diets (P = 0.02). RCT that substituted n-6 PUFA for TFA and SFA without simultaneously increasing n-3 PUFA produced an increase in risk of death that approached statistical significance (RR 1.16; 95 % CI 0.95, 1.42). Advice to specifically increase n-6 PUFA intake, based on mixed n-3/n-6 RCT data, is unlikely to provide the intended benefits, and may actually increase the risks of CHD and death.

Imaging incorporation of circulating docosahexaenoic acid into the human brain using positron emission tomography.

Docosahexaenoic acid (DHA; 22:6n-3) is a critical constituent of the brain, but its metabolism has not been measured in the human brain in vivo. In monkeys, using positron emission tomography (PET), we first showed that intravenously injected [1-(11)C]DHA mostly entered nonbrain organs, with approximately 0.5% entering the brain. Then, using PET and intravenous [1-(11)C]DHA in 14 healthy adult humans, we quantitatively imaged regional rates of incorporation (K*) of DHA. We also imaged regional cerebral blood flow (rCBF) using PET and intravenous [(15)O]water. Values of K* for DHA were higher in gray than white matter regions and correlated significantly with values of rCBF in 12 of 14 subjects despite evidence that rCBF does not directly influence K*. For the entire human brain, the net DHA incorporation rate J(in), the product of K*, and the unesterified plasma DHA concentration equaled 3.8 +/- 1.7 mg/day. This net rate is equivalent to the net rate of DHA consumption by brain and, considering the reported amount of DHA in brain, indicates that the half-life of DHA in the human brain approximates 2.5 years. Thus, PET with [1-(11)C]DHA can be used to quantify regional and global human brain DHA metabolism in relation to health and disease.

An n-3 fatty acid deficient diet affects mouse spatial learning in the Barnes circular maze.

Deficiency in n-3 fatty acids has been accomplished through the use of an artificial rearing method in which ICR mouse pups were hand fed a deficient diet starting from the 2nd day of life. There was a 51% loss of total brain DHA in mice with an n-3 fatty acid-deficient diet relative to those with a diet sufficient in n-3 fatty acids. n-3 fatty acid adequate and deficient mice did not differ in terms of locomotor activity in the open field test or in anxiety-related behavior in the elevated plus maze. The n-3 fatty acid-deficient mice demonstrated impaired learning in the reference-memory version of the Barnes circular maze as they spent more time and made more errors in search of an escape tunnel. No difference in performance between all dietary groups in the cued and working memory version of the Barnes maze was observed. This indicated that motivational, motor and sensory factors did not contribute to the reference memory impairment.

Increased dietary intake of omega-3-polyunsaturated fatty acids reduces pathological retinal angiogenesis.

Many sight-threatening diseases have two critical phases, vessel loss followed by hypoxia-driven destructive neovascularization. These diseases include retinopathy of prematurity and diabetic retinopathy, leading causes of blindness in childhood and middle age affecting over 4 million people in the United States. We studied the influence of omega-3- and omega-6-polyunsaturated fatty acids (PUFAs) on vascular loss, vascular regrowth after injury, and hypoxia-induced pathological neovascularization in a mouse model of oxygen-induced retinopathy. We show that increasing omega-3-PUFA tissue levels by dietary or genetic means decreased the avascular area of the retina by increasing vessel regrowth after injury, thereby reducing the hypoxic stimulus for neovascularization. The bioactive omega-3-PUFA-derived mediators neuroprotectinD1, resolvinD1 and resolvinE1 also potently protected against neovascularization. The protective effect of omega-3-PUFAs and their bioactive metabolites was mediated, in part, through suppression of tumor necrosis factor-alpha. This inflammatory cytokine was found in a subset of microglia that was closely associated with retinal vessels. These findings indicate that increasing the sources of omega-3-PUFA or their bioactive products reduces pathological angiogenesis. Western diets are often deficient in omega-3-PUFA, and premature infants lack the important transfer from the mother to the infant of omega-3-PUFA that normally occurs in the third trimester of pregnancy. Supplementing omega-3-PUFA intake may be of benefit in preventing retinopathy.

Haploinsufficiency is not the key mechanism of pathogenesis in a heterozygous Elovl4 knockout mouse model of STGD3 disease.

PURPOSE: Autosomal dominant Stargardt-like (STGD3) disease results from mutations in the ELOVL4 gene (elongation of very-long-chain fatty acids). This study was undertaken to characterize a mouse model with a targeted deletion of Elovl4 and to explore the role of this gene in retinal/macular degeneration. METHODS: A construct targeted to exon 2 of the Elovl4 gene was used to suppress expression of the gene. Elovl4 homozygous pups were nonviable and were not available for study. Hence, the analysis was performed on heterozygous Elovl4(+/-) mice 16 to 22 month of age and littermate wild-type (WT) control mice of the same age. Characterization included examining gene message and protein levels, electroretinogram (ERG), retinal morphology and ultrastructure, and plasma and retinal fatty acid composition. RESULTS: Although the level of Elovl4 mRNA was reduced in Elovl4(+/-) retinas, only minimal morphologic abnormalities were found, and the retinal (ERG) function was essentially normal in Elovl4(+/-) retinas compared with the WT control retinas. Systemic fatty acid profiles of Elovl4(+/-) mice were unremarkable, although the concentration of several fatty acids was significantly lower in Elovl4(+/-) retinas, particularly the monounsaturated fatty acids. CONCLUSIONS: The detailed characterization of this animal model provides the first in vivo evidence that Elovl4 haploinsufficiency is not the underlying key disease mechanism in STGD3. The results are consistent with a dominant negative mechanism for the deletion mutation. The Elovl4 knockout mouse is one of three complementary animal models that will help elucidate the disease mechanism.

Incomplete replacement of docosahexaenoic acid by n-6 docosapentaenoic acid in the rat retina after an n-3 fatty acid deficient diet.

When sources of n-3 fatty acids are not present in the diet, nervous system docosahexaenoic acid (22:6n3) is replaced by docosapentaenoic acid (22:5n6). Dams were fed either an n-3 deficient diet or one containing alpha-linolenic acid (18:3n3) and 22:6n3 throughout pregnancy and lactation. Their male offspring at weaning also received either the n-3 deficient or n-3 adequate diets and were sacrificed at 5, 10, 20, 50 and 91 days of age. Retinal lipids were extracted and analysed by gas chromatography for fatty acyl content. The percentage of retinal 22:6n3 increased continuously over the 13 week course of the experiment but reached its maximal concentration around day 20. Non-reciprocal replacement of 22:6n3 by 22:5n6 was observed at postnatal day 20 and 50 but not at other time points. Complete replacement of 22:6n3 was apparent if elevations in both 22:5n6 and docosatetraenoic acid (22:4n6) were considered. These data indicate that during the rapid period of accretion of retinal 22:6n3 around postnatal day 20, the supply of 22:5n6 to the retina was inadequate to completely replace 22:6n3 in n-3 deficient rats.

Fatty acid formula supplementation and neuromotor development in rhesus monkey neonates.

Docosahexaenoic acid (DHA) is an omega-3 fatty acid that is highly concentrated in CNS tissues. Although breast milk contains the fatty acids DHA and arachidonic acid, infant formulas marketed in North America do not contain these nutrients. The potential deleterious effects of rearing infants with formulas devoid of these nutrients was assessed by comparing nursery-reared rhesus macaque infants (Macaca mulatta) fed standard formula with infants fed standard formula supplemented with physiologically relevant concentrations of DHA (1.0%) and arachidonic acid (1.0%). Neurobehavioral assessments were conducted on d 7, 14, 21, and 30 of life using blinded raters. The 30-min assessment consisted of 45 test items measuring orienting, temperament, reflex capabilities, and motor skills. Plasma concentrations of DHA in standard formula-fed infants were significantly lower than those fed supplemented formula or mother-raised (breast-fed) infants; however, infants fed the supplemented formula exhibited higher arachidonic acid levels than either mother-reared infants or infants fed standard formula. Infant monkeys fed the supplemented formula exhibited stronger orienting and motor skills than infants fed the standard formula, with the differences most pronounced during d 7 and 14. This pattern suggests an earlier maturation of specific visual and motor abilities in the supplemented infants. Supplementation did not affect measures of activity or state control, indicating no effect on temperament. These data support the assertion that preformed DHA and arachidonic acid in infant formulas are required for optimal development.