Docosahexaenoic acid synthesis from alpha-linolenic acid is inhibited by diets high in polyunsaturated fatty acids.

The conversion of the plant-derived omega-3 (n-3) α-linolenic acid (ALA, 18:3n-3) to the long-chain eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) can be increased by ALA sufficient diets compared to ALA deficient diets. Diets containing ALA above an optimal level result in no further increase in DHA levels in animals and humans. The present study evaluates means of maximizing plasma DHA accumulation by systematically varying both linoleic acid (LA, 18:2n-6) and ALA dietary level. Weanling rats were fed one of 54 diets for three weeks. The diets varied in the percentage of energy (en%) of LA (0.07-17.1 en%) and ALA (0.02-12.1 en%) by manipulating both the fat content and the balance of vegetable oils. The peak of plasma phospholipid DHA (>8% total fatty acids) was attained as a result of feeding a narrow dietary range of 1-3 en% ALA and 1-2 en% LA but was suppressed to basal levels (∼2% total fatty acids) at dietary intakes of total polyunsaturated fatty acids (PUFA) above 3 en%. We conclude it is possible to enhance the DHA status of rats fed diets containing ALA as the only source of n-3 fatty acids but only when the level of dietary PUFA is low (<3 en%).

Transforming growth factor beta in human milk does not change in response to modest intakes of docosahexaenoic acid.

Long-chain polyunsaturated fatty acids have been associated with aspects of immune regulation including cytokine production. The purpose of this study was to investigate the effect of maternal dietary supplementation with tuna oil, rich in docosahexaenoic acid (DHA), on the concentration of transforming growth factor beta 1 (TGFbeta1) and TGFbeta2 in breast milk. In this randomized, dietary intervention trial, mothers of term infants consumed a daily supplement of 2000 mg oil containing either placebo (n = 40), 300 mg DHA (n = 40), or 600 mg DHA (n = 40). The DHA increase in milk and plasma was proportional to dietary DHA. There was no relationship between milk DHA status and TGFbeta1 and TGFbeta2 levels.

Biochemical effects of a diet containing foods enriched with n-3 fatty acids.

BACKGROUND: Results of many studies indicate that consumption of n-3 fatty acids can benefit persons with cardiovascular disease and rheumatoid arthritis. However, encapsulated fish oil is unlikely to be suited to lifetime daily use and recommendations to increase fish intake have not been effective. OBJECTIVE: The objective was to examine the effectiveness of a diet that incorporates foods rich in n-3 fatty acids in elevating tissue concentrations of eicosapentaenoic acid and in suppressing the production of inflammatory mediators. DESIGN: Healthy male volunteers were provided with foods that were enriched in alpha-linolenic acid (cooking oil, margarine, salad dressing, and mayonnaise) and eicosapentaenoic and docosahexaenoic acids (sausages and savory dip) and with foods naturally rich in n-3 fatty acids, such as flaxseed meal and fish. Subjects incorporated these products into their food at home for 4 wk. Fatty acid intakes, cellular and plasma fatty acid concentrations, and monocyte-derived eicosanoid and cytokine production were measured. RESULTS: Analyses of dietary records indicated that intake of eicosapentaenoic acid plus docosahexaenoic acid averaged 1.8 g/d and intake of alpha-linolenic acid averaged 9. 0 g/d. These intakes led to an average 3-fold increase in eicosapentaenoic acid in plasma, platelet, and mononuclear cell phospholipids. Thromboxane B(2), prostaglandin E(2), and interleukin 1beta synthesis decreased by 36%, 26%, and 20% (P < 0.05), respectively. CONCLUSIONS: Foods that are strategically or naturally enriched in n-3 fatty acids can be used to achieve desired biochemical effects without the ingestion of supplements or a change in dietary habits. A wide range of n-3-enriched foods could be developed to support large-scale programs on the basis of the therapeutic and disease-preventive effects of n-3 fatty acids.

A critical appraisal of the role of dietary long-chain polyunsaturated fatty acids on neural indices of term infants: a randomized, controlled trial.

OBJECTIVE: To determine whether dietary long-chain polyunsaturated fatty acids (LCPUFA), such as docosahexaenoic acid (DHA) and arachidonic acid, affect visual evoked potential (VEP) acuity of formula-fed infants, relative to breastfed infants. A secondary objective was to assess the effect of LCPUFA on Bayley's mental developmental index (MDI) and psychomotor developmental index (PDI). METHODS: Formula-fed infants were randomly allocated, in a double-blind manner, to either a placebo (no LCPUFA; n = 21), DHA supplemented (n = 23), or DHA+arachidonic acid supplemented formula (n = 24). Infants were fed their assigned formula from the first week of life until 1 year of age. A parallel reference group of breastfed infants was recruited and followed (n = 46). Infant VEP acuity was assessed at 16 and 34 weeks, and Bayley's MDI and PDI were assessed at 1 and 2 years of age. RESULTS: There were no differences among the randomized formula groups for VEP acuity at either 16 or 34 weeks of age. Breastfed infants had better VEP acuity at 34 weeks of age, but not at 16 weeks, compared with all formula-fed infants. Bayley's MDI and PDI were similar in the 3 formula-fed groups at 1 and 2 years. Breastfed infants had higher MDI scores than formula-fed infants at 2 years of age even after adjusting for environmental variables. CONCLUSIONS: LCPUFA supplementation did not influence VEP acuity development in these well-nourished, formula-fed infants.

Dietary long-chain polyunsaturated fatty acids do not influence growth of term infants: A randomized clinical trial.

OBJECTIVE: To determine if dietary long-chain polyunsaturated fatty acids (LCPUFA) affect the growth of formula-fed infants relative to breastfed infants. METHODS: A randomized, double-blind trial of three formula-fed groups and a parallel reference group of breastfed infants was conducted. The three treatments were a placebo (no LCPUFA), docosahexaenoic acid (DHA) supplemented, and DHA plus arachidonic acid supplemented formulas fed for 12 months. Infant weight, length, head circumference, and fatty acid status were assessed at 6, 16, 34 weeks, and 1 year of age. Anthropometrics were repeated at 2 years of age. RESULTS: There were no differences between the randomized formula groups for weight, length, or head circumference even after adjustment for gender, gestational age, and the actual age at assessment. Post hoc regressions demonstrated a small negative association between DHA status at 16 weeks of age and weight at 1 and 2 years. CONCLUSIONS: Dietary LCPUFA do not influence growth of healthy term infants to a clinically significant degree.

Effect of increasing breast milk docosahexaenoic acid on plasma and erythrocyte phospholipid fatty acids and neural indices of exclusively breast fed infants.

OBJECTIVES: To determine the effect of increasing docosahexaenoic acid (DHA, 22:6 n-3) in breast milk on infant fatty acid profiles. A secondary aim was to examine aspects of neural development. DESIGN AND SETTING: Double blind, placebo controlled study of infants recruited from postnatal wards at Flinders Medical Centre. SUBJECTS: Fifty-two healthy term infants who were breast fed for at least 12 weeks and were from middle class families. INTERVENTION: Breast milk with DHA concentrations that ranged from 0.1-1.7% of total fatty acids. This was achieved by supplementation of the maternal diet for the first 12 weeks post partum. RESULTS: Breast milk with DHA was related to infant plasma (r = 0.89, P < 0.001) and erythrocyte (r = 88, P < 0.001) phospholipids in a saturable curvilinear manner so that breast milk DHA above 0.8% of total fatty acids resulted in little further increase in infant plasma or erythrocyte DHA levels. The rise in plasma and erythrocyte DHA was approximated by a fall in total n-6 polyunsaturated fatty acids. We could detect no relationship between visual evoked potential acuity (measured at 12 and 16 weeks) of infants by either the dietary grouping or the DHA status of individuals. A stepwise multiple regression showed that infant erythrocyte DHA at 12 weeks and home stimulation were the only independent factors associated with Bayley's MDI at 1 y (adjusted model r2 = 0.18, P < 0.005); while at 2 y gender and social score of the spouse were the only significant predictors of Bayley's MDI (adjusted model r2 = 0.22, P < 0.005). CONCLUSIONS: Increasing breast milk DHA levels caused a dose dependent saturable increase in infant plasma and erythrocyte phospholipid DHA. There were no long-term effects of infant DHA status on indices of neurodevelopment.

Effect of maternal docosahexaenoic acid (DHA) supplementation on breast milk composition.

OBJECTIVE: To assess the effect of varying maternal intake of docosahexaenoic acid (DHA, 22 : 6n-3), in the absence of other dietary polyunsaturates, on breast milk fatty acids. DESIGN AND INTERVENTION: Lactating mothers were randomised on day 5 post-partum to groups consuming equal numbers of capsules but containing either placebo or an oil containing DHA (43%) as its only polyunsaturate to receive 0, 0.2, 0.4, 0.9, 1.3 g DHA/day. Breast milk fatty acids as well as maternal plasma and erythrocyte phospholipids were assessed at 12 weeks post partum by capillary gas chromatography. RESULTS: Breast milk DHA levels ranged from 0.2 to 1.7% of total fatty acids and increased in a dose dependent manner (r2 = 0.89, P < 0.01). Maternal plasma (r2 = 0.71, P < 0.01) and erythrocyte (r2 = 0.77, P < 0.01) phospholipid DHA levels increased and were also strongly associated with dietary dose of DHA. Increasing maternal dietary doses of DHA did not affect breast milk arachidonic acid (AA, 20 : 4n-6) levels or antioxidant status as measured by plasma vitamin A or E levels. CONCLUSIONS: Our results have demonstrated that DHA in the diet has a strong, specific and dose-dependent effect on breast milk DHA.

Effect of dietary docosahexaenoic acid on brain composition and neural function in term infants.

There is a need to determine whether there is a dietary requirement for docosahexaenoic acid (DHA, 22:6n-3) by term infants to achieve their full developmental potential. Studies of brain fatty acid composition demonstrated that infants who were breast fed had greater levels of cerebral cortex DHA than did infants who were formula fed, suggesting that DHA in the cerebrum is dependent on a supply in the diet. Some physiological studies reported that electrophysiological and behavioral assessments of visual function were improved in breast-fed infants relative to those fed formula and that this was related to the length of breast feeding. While some randomized studies of DHA supplementation of infant formula to term infants demonstrated that the visual function of formula-fed infants could be improved to breast-fed levels by adding DHA to formula, others failed to demonstrate an effect. Variations in dietary treatments and methods of assessment make comparison of the studies difficult. Further work is necessary to rigorously establish if there are long-term benefits of dietary DHA to the term infant.

Is dietary docosahexaenoic acid essential for term infants?

There is a need to determine whether there is a dietary requirement for docosahexaenoic acid (DHA, 22:6 omega 3) by term infants to achieve their full developmental potential. Studies of brain fatty acid composition have demonstrated that infants who were breast fed have greater levels of cerebral cortex DHA than infants who were formula fed, suggesting that DHA in the cerebrum is dependent on a supply in the diet. Some physiological studies report that electrophysiological and behavioral assessments of visual function are improved in breast-fed infants relative to those fed formula, and that this is related to the level of DHA in their erythrocytes, whereas other studies demonstrate equivalent visual function between breast- and formula-fed infants. However, randomized studies of DHA supplementation of infant formula demonstrate that the visual function of formula-fed infants can be improved to breast-fed levels by adding DHA to formula. Further work is necessary to establish if there are long-term benefits of dietary DHA to the term infant.

Erythrocyte fatty acids of term infants fed either breast milk, standard formula, or formula supplemented with long-chain polyunsaturates.

The purpose of our study was to assess whether a supplement of fish oil (FO) and evening primrose oil (EPO) for formula-fed infants was capable of avoiding reductions in erythrocyte docosahexaenoic acid (DHA, 22:6n-3) and arachidonic acid (AA, 20:4n-6) associated with standard formula feeding. Healthy, term infants, whose mothers chose to formula feed, were randomized to either a placebo or supplemented formula for their first 30 wk of life. A reference group of beast-fed infants also was enrolled. Erythrocyte fatty acids were measured by capillary gas chromatography on day 5 and in weeks 6, 16, and 30. Supplementation of formula with 0.36% of total fatty acids as DHA resulted in erythrocyte DHA being maintained at or above breast-fed levels for the entire 30-wk study period, and breast feeding (0.21% DHA) resulted in a modest fall in erythrocyte DHA relative to baseline (day 5) values. The level of erythrocyte DHA in placebo formula-fed infants was halved by week 16. AA levels decreased in all infants in the first six weeks, but the levels in breast- and placebo formula-fed infants increased with age and returned to approximate baseline (day 5) values by 16 and 30 wk of age, respectively. Erythrocyte AA in FO+EPO-supplemented infants remained low and below breast- and placebo formula-fed levels. Our data suggest that dietary supplementation with DHA at 0.36% total fatty acids results in erythrocyte DHA levels above those found in breast-fed infants. EPO supplementation was not effective at maintaining erythrocyte AA when given with FO.

Differences in fatty acid composition of immature and mature articular cartilage in humans and sheep.

Chondrocytes are imbedded in an avascular, highly charged extracellular matrix which could form a barrier to the transfer of dietary essential fatty acids (EFA) to chondrocytes. A study was designed to assess the composition of immature and mature joint cartilage with respect to essential and nonessential fatty acids relevant to EFA deficiency. Cartilage and muscle samples were obtained from human fetus, infant and adult cadavers, and from fetal and mature sheep. Lipid extracts were prepared and the fatty acid composition determined. In human and sheep joint cartilage, linoleic acid (LA; 18:2n-6) content was lower, and n-9 eicosatrienoic acid (ETrA; 20:3n-9) and arachidonic acid (AA; 20:4n-6) were higher in fetuses compared to mature subjects. An intermediate pattern was seen in infant cartilage. n-3 Fatty acids tended to be higher in fetal than in mature cartilage in humans and in sheep. In human muscle (and in other noncartilaginous comparison tissues), similar differences between fetuses and adults were seen in LA and AA, but not in ETrA. In fetal sheep muscle, very low LA, reduced AA and raised ETrA levels compared to mature sheep muscle were seen. However, although the pattern is characteristic of EFA deficiency, the abundance of n-6 EFA in liver and spleen of human fetuses and of n-3 EFA in liver and spleen of fetal sheep suggests that placental transfer of EFA is not likely to be limiting. During fetal development, the metabolism of fatty acids is distinctive and differs between the species. ETrA appears to be a readily measurable component of some tissues at certain stages of development when its presence in tissues does not indicate EFA deficiency.

Sudden infant death syndrome: effect of breast and formula feeding on frontal cortex and brainstem lipid composition.

METHODOLOGY: Docosahexaenoic acid levels were measured by gas chromatography in samples of frontal lobe and brainstem taken from 28 and 26 infants, respectively, who had died of sudden infant death syndrome (SIDS). RESULTS: Significantly higher levels of docosahexaenoic acid were present in the frontal lobe tissues derived from the 13 breast fed infants (age range = 3.3-36.3 weeks; mean 15.9 +/- 11.3 weeks) compared to the 15 formula fed infants (age range = 6.9-47.7 weeks; mean 19.3 +/- 10.6 weeks); mean (+/- s.d.) levels were 8.5 +/- 1.1% and 7.6 +/- 0.8% of total fatty acids (P = 0.019). There was, however, no significant difference in brainstem docosahexaenoic acid levels between breast and formula fed infants. CONCLUSIONS: Given these variable findings, further investigation of the relationship between dietary fatty acid intake and cerebral lipid levels may help to clarify whether different modes of feeding have a role in the pathogenesis of SIDS.

Ratios of linoleic acid to alpha-linolenic acid in formulas for term infants.

Commercial infant formulas with a ratio of linoleic acid (LA) to alpha-linolenic acid (ALA) of 10:1 or higher are nutritionally inadequate; the tissue levels of docosahexaenoic acid (DHA) are lower and the visual function indices are reduced in infants who are fed these formulas. All the evidence points to using LA:ALA ratios of less than 8:1, but there has been only one study in infants that used formulas with reduced LA:ALA ratios, and only biochemical indices were monitored. There is a need for both short-term studies to establish the ratios of LA to ALA that will make possible the accumulation of DHA to levels close to those in breast-fed infants and long-term trials to determine the effects of such fat blends on growth and development.

Effect of dietary supplementation with n-9 eicosatrienoic acid on leukotriene B4 synthesis in rats: a novel approach to inhibition of eicosanoid synthesis.

Studies were undertaken to assess the biochemical effects of dietary supplementation with n-9 eicosatrienoic acid (ETrA), an arachidonic acid analogue that is normally present in cell membranes at very low levels but is raised in the presence of essential fatty acid deficiency (EFAD). The incorporation of dietary ETrA into rat neutrophils and its effect on A23187-stimulated 5-lipoxygenase metabolism in these cells was examined; in addition, the effect of ETrA was compared with that of another arachidonic acid analogue, eicosapentaenoic acid (EPA), which is known to accumulate in cell membranes and inhibit synthesis of leukotriene B4 (LTB4) a product of the 5-lipoxygenase metabolic pathway. Rats were fed a defined diet that was sufficient in essential fatty acids and that contained EPA or ETrA (0.014% of energy) or no added fatty acid, for 3 wk. In the cells from ETrA-fed rats, LTB4 synthesis was inhibited relative to control values, but synthesis of the other products of 5-lipoxygenase metabolism, 5-hydroxyeicosatetraenoic acid (5-HETE) and the all-trans isomers of LTB4, were not inhibited. This pattern indicates inhibition of LTA hydrolase in ETrA-fed rats. In EPA-fed rats, there was inhibition of LTB4 and the all-trans isomers of LTB4, but there was no inhibition of 5-HETE. This pattern indicates inhibition of LTA synthase in EPA-fed rats. The results establish that dietary ETrA effectively inhibits synthesis of the inflammatory mediator, LTB4, and suggest that ETrA may confer antiinflammatory benefits similar to those observed with EFAD or dietary fish oil (which contains EPA). Because ETrA is substantially less unsaturated than EPA, it can be expected to have greater chemical stability, which could be an important practical advantage when used as a dietary constituent or supplement.

Simple relationships exist between dietary linoleate and the n-6 fatty acids of human neutrophils and plasma.

Eicosanoids, the enzymatically oxygenated products of arachidonic acid (AA), appear to be overproduced in some disorders of inflammation. Dietary strategies for decreasing tissue AA require information on the relationships between dietary linoleic acid (LA) and tissue concentrations of AA. The use of either high- or low-LA spreads and cooking oils by healthy male volunteers resulted in a range of LA intakes of 2.5-17.5% of energy, as estimated by diet-diary analysis. Analysis of LA and AA concentrations in neutrophils and plasma lipid fractions from these subjects indicated that there were positive linear relationships between dietary LA and the LA concentrations in neutrophil phospholipids, plasma triglycerides, and plasma cholesteryl esters. By contrast, differences in dietary LA within a broad range were not associated with differences in concentrations of AA in these same neutrophil and plasma fractions. AA concentrations were decreased by supplementation of the diet with 4 g fish oil (1.6 g eicosapentaenoic acid, 0.3 g docosahexaenoic acid). The results suggest that the LA content of tissue lipids may be used to estimate LA intake, and the reduction of dietary LA by using standard dietary strategies is not likely to lead to reduction in tissue AA whereas this can be accomplished by fish-oil supplementation.

Effect of n-3 and n-6 dietary fats on the lipoxygenase products from stimulated rat neutrophils.

Fish oil was fed to rats in combination with an equal amount of olive, sunflower or linseed (flax) oil in semisynthetic diets for 3 weeks. Following stimulation of isolated neutrophils with calcium ionophore the levels of leukotrienes (LT) were determined by HPLC. Graphical presentation of the resultant data show a direct linear relationship between LTB production and substrate concentration with no preferential conversion of n-3 or n-6 substrates. In addition the results highlighted the greater conversion of eicosapentaenoic acid (EPA) and arachidonic acid (AA) to 5-hydroxy metabolites in stimulated neutrophils. There is no suggestion in our results of inhibition of any of the enzymatic conversion steps between EPA or AA and LTB production by any of the dietary fatty acids except by altering the EPA/AA ratio in neutrophil membranes.

Incorporation of dietary oleate, linoleate, alpha-linolenate and eicosapentaenoate into the plasma lipid fractions of four strains of rat.

Four strains of rat (Dark Agouti, DA; Ginger Hooded, GH; Portion, P; Hooded Wistar, HW) were fed elemental diets containing different sources of fat at the 10% (w/w) level. The dietary fats used included the following oils; olive (rich in oleate), sunflower (rich in linoleate), linseed (rich in alpha-linolenate) and fish (rich in eicosapentaenoate and docosahexaenoate). Differences between strains in response to individual diets were modest compared with the much greater differences achieved by the dietary treatments. In general, the changes in polyunsaturated fatty acid (PUFA) levels in the plasma lipids of all rat strains followed the major PUFA in the diet. There were, however, strong interactions between dietary n-6 and n-3 PUFA which affected not only the level of particular PUFA in lipid fractions but also the lipid fraction in which a particular PUFA appeared. Our findings indicate that a response to dietary fats in the plasma lipids of one strain of rat can be expected to occur with relatively minor variations in other commonly used rat strains.

The effect of dietary supplementation with eicosapentaenoic acid on the phospholipid and fatty acid composition of erythrocytes of marmoset.

Adult male marmoset monkeys were fed eicosapentaenoic acid (20:5n-3) as the ethyl ester in diets containing either 32% (reference diet, no added cholesterol) or 7% (atherogenic diet with 0.2% added cholesterol) linoleic acid (18:2n-6) for 30 wk. No changes were seen in the level of phosphatidylcholine (PC) or phosphatidylethanolamine (PE) but minor changes were observed in both the sphingomyelin (SPM) and phosphatidylinositol plus phosphatidylserine (PI+PS) fractions of erythrocyte lipids. The extent of total n-3 fatty acid incorporation into membrane lipids was higher in atherogenic diets (polyunsaturated/monounsaturated/saturated (P/M/S) ratio 0.2:0.6:1.0) than reference diets (P/M/S ratio 1:1:1) and this was true for both PE (33.4 +/- 1.0% vs 24.3 +/- 1.1%) and PC (9.3 +/- 0.5% vs 4.9 +/- 0.3%). Although suitable controls for cholesterol effects were not included in the study, earlier results obtained with marmosets lead us to believe such effects were probably small. Regardless of basic diet (atherogenic, reference), 20:5n-3 was preferentially incorporated into PE (10.8 +/- 0.2%, 6.0 +/- 0.02%) while smaller amounts were incorporated into PC (6.9 +/- 0.4%, 3.2 +/- 0.2%). The major n-3 polyunsaturated fatty acid found in PE in response to dietary 20:5n-3 was the elongation metabolite 22:5n-3 in both the atherogenic (17.7 +/- 0.7%) and reference (14.3 +/- 1.0%) dietary groups; 22:6n-3 levels were less affected by diet (4.7 +/- 0.3% and 3.9 +/- 0.2%, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Linoleate inhibits EPA incorporation from dietary fish-oil supplements in human subjects.

Thirty healthy male subjects were randomly allocated into one of two treatment groups: group H subjects were maintained on a high-linoleic acid (LA) diet with the saturated fatty acids kept low and those in group L were kept on a low-LA, low saturate diet. After a 3-wk run-in period, subjects consumed a fish-oil supplement containing 1.6 g eicosapentaenoic acid (EPA)/d and 0.32 g docosahexaenoic acid as triglycerides for a further 4 wk. The diets alone resulted in a significant change in neutrophil phospholipid LA (H = 12.7 +/- 2.9%, L = 9.0 +/- 0.9%; P less than 0.05). Dietary supplementation with fish oil resulted in a significant increase in EPA in neutrophil phospholipids that was greater in group L (mean 2.0 +/- 0.4%) than group H (mean 1.5 +/- 0.3%; P less than 0.005). Reductions in arachidonic acid concentrations in neutrophil membranes were not different, nor could differences in leukotriene B4 production be detected. Our study indicates that the ingestion of n-6 fatty acids within the diet is an important determinant of EPA incorporation into neutrophil membranes.

Gamma linolenic acid (GLA) content of encapsulated evening primrose oil products.

The fatty acid composition of 16 brands of evening primrose oil (EPO) capsules was determined by capillary gas chromatography. Fourteen of these EPO brands contained gamma-linolenic acid (GLA) levels between 7% and 10% (mean, 8.7; range, 1.9-10.5%) and there was generally good agreement between the level of GLA claimed by the manufacturer and the level determined by analysis. Low levels of the monoenes 22:1 and 24:1 found in some brands may indicate contamination of EPO with borage oil.