n-6 Docosapentaenoic acid is not a predictor of low docosahexaenoic acid status in Canadian preschool children

BACKGROUND: The n-3 fatty acid docosahexaenoic acid (DHA; 22:6n-3) is important for neural and visual functional development. In animals, 22:6n-3 deficiency is accompanied by increased docosapentaenoic acid (DPA; 22:5n-6), which suggests that the ratio of 22:6n-3 to 22:5n-6 could be a useful biochemical marker of low n-3 fatty acid status. The n-3 fatty acid status of preschool children has not been described, and data are lacking on whether low 22:6n-3 is accompanied by high 22:5n-6 in humans. OBJECTIVE: We determined n-3 fatty acid status and investigated the relation between 22:6n-3 and 22:5n-6 in children. DESIGN: In Canadian children aged 18-60 mo (n = 84), the n-3 and n-6 fatty acid status of erythrocyte phosphatidylethanolamine was measured, and dietary fat intake was estimated by using a food-frequency questionnaire. RESULTS: The mean (+/- SEM) 22:6n-3 concentration in erythrocyte phosphatidylethanolamine among children was 3.06 +/- 0.13 g/100 g fatty acids (5th-95th percentiles: 1.43-5.79 g/100 g fatty acids). Concentrations of 22:5n-6 increased with increasing 22:6n-3 concentrations in erythrocyte phosphatidylethanolamine (P < 0.01). Mean intakes of linoleic acid (18:2n-6), linolenic acid (18:3n-3), and trans fatty acids were 3.6 +/- 0.2%, 0.7 +/- 0.5%, and 2.0 +/- 1.3%, respectively. Phosphatidylethanolamine 22:6n-3 and 22:5n-3 concentrations were inversely related to the intakes of 18:2n-6 and trans fatty acids, but not to those of total fat or n-3 fatty acids. CONCLUSIONS: The concentration of 22:5n-6 is not a useful biochemical marker of low n-3 fatty acid intake or status in the membrane phosphatidylethanolamine of preschool children. High intakes of 18:2n-6 and trans fatty acids could compromise the incorporation of 22:6n-3 into membrane phospholipids.     

Comparison between plasma and erythrocyte fatty acid content as biomarkers of fatty acid intake in US women

BACKGROUND: Erythrocyte fatty acids may be superior to plasma fatty acids for reflecting long-term fatty acid intake because of less sensitivity to recent intake and a slower turnover rate. OBJECTIVE: The objective was to compare the fatty acid content of erythrocytes with that of plasma with respect to their abilities to reflect usual fatty acid intake. DESIGN: Fatty acids in plasma and erythrocytes were measured by capillary gas-liquid chromatography in 306 US women aged 43-69 y. Fatty acid intake was assessed with a food-frequency questionnaire, which was validated for measuring intakes of various fatty acids. RESULTS: Docosahexaenoic acid (DHA, 22:6n-3) in erythrocytes and plasma provided the strongest correlations with its intake, but erythrocyte DHA concentrations [Spearman's partial correlation coefficient (r(s))=0.56] were better than plasma DHA concentrations (r(s)=0.48) as a biomarker. Total trans fatty acids (r(s)=0.43) and total 18:1 trans isomers (r(s)=0.42) in erythrocytes were also more strongly correlated with intake than were those in plasma (r(s)=0.30 and r(s)=0.29, respectively). Moderate correlations were observed for linoleic acid (18:2n-6; erythrocytes, r(s)=0.24; plasma, r(s)=0.25), alpha-linolenic acid (18:3n-3; erythrocytes, r(s)=0.18; plasma, r(s)=0.23), and eicosapentaenoic acid (20:5 n-3; erythrocytes, r(s)=0.38; plasma, r(s)=0.21). For polyunsaturated and trans fatty acids, correlations between intakes and biomarkers improved moderately when average intakes over previous years were used. CONCLUSION: Erythrocyte n-3 fatty acids of marine origin and trans fatty acid content are suitable biomarkers for long-term intake.     

Dietary (n-3) fatty acids alter fatty acid composition and prostaglandin synthesis in rat testis

The objective of this study was to determine the efficacy of linolenic acid [18:3(n-3)], compared with the long-chain (n-3) fatty acids in fish oil, in suppressing arachidonic acid [20:4(n-6)] metabolism in rat testis. Six groups of rats were fed three levels of 18:3(n-3) or fish oil, and the fatty acid composition of testis parenchyma lipids and prostaglandin (PG) I2 synthesis by tunica were determined after 12 wk. Levels of docosapentaenoic acid [22:5(n-6)], the major 22-carbon fatty acid in rat testis lipids, were significantly depressed compared with the control by both linolenic acid and fish oil; however, testis weights were not affected significantly. Arachidonic acid levels also were depressed significantly in testis lipids by dietary (n-3) fatty acids, but the decreases were not as pronounced as those observed in other tissues. The synthesis of PGI2 was significantly reduced compared with the control by (n-3) fatty acid feeding, but there were no differences among the experimental groups. Both 18:3(n-3) and the longer-chain (n-3) fatty acids from fish oil reduce levels of 20:4(n-6) and 22:5(n-6) in testis lipids and the capacity of the tunica to synthesize PGI2, but these fatty acids seem to cause no defect in testicular development as indicated by weight.     

Essential fatty acid status in southern Thai preschool children

Essential fatty acid (EFA) status was assessed in 15 Southern Thai preschool children. The mean (+/- SD) serum linoleate (18:2 n-6), arachidonate (20:4 n-6), linolenate (18:3 n-3), eicosapentaenoate (20:5 n-3), and docosahexaenoate (22:6 n-3) percentages in the preschool children were 21.7 +/- 4.0, 6.0 +/- 1.2, 0.4 +/- 0.1, 1.2 +/- 0.8, and 4.4 +/- 1.3, respectively. Since EFA composition of total serum lipids in healthy children are not available and age and sex do not largely influence these parameters, the results of the preschool children were compared with those of 10 healthy Bangkok adults. The corresponding figures of the aforementioned fatty acids in adults were 34.9 +/- 8.5, 4.6 +/- 1.5, 0.8 +/- 0.4, 0.5 +/- 0.4, and 1.6 +/- 0.8, respectively. The data indicate linoleate and linolenate depletion in the preschool children. This was due to their low fat intake and lack of consumption of vegetable oil rich in linoleic and linolenic acids. Their high serum arachidonate percentage was probably due to the increased conversion of 18:2 n-6 to 20:4 n-6 in the presence of linolenate depletion. The significantly higher serum 20:5 n-3 and 22:6 n-3 percentages in the preschool children should be due to direct consumption of these two n-3 fatty acids from fish intake.     

Docosahexaenoic and arachidonic acid prevent a decrease in dopaminergic and serotoninergic neurotransmitters in frontal cortex caused by a linoleic and alpha-linolenic acid deficient diet in formula-fed piglets.

This study examined the effects of diets deficient (D) in linoleic [18:2(n-6)] and linolenic acid [18:3(n-3)] at 0.8 and 0.05% energy, respectively, or adequate (C) in 18:2(n-6) and 18:3(n-3) at 8.3 and 0.8% energy, respectively, without (-) or with (+) 0.2% energy arachidonic [20:4(n-6)] and 0.16% energy docosahexaenoic [22:6(n-3)] acid in piglets fed from birth to 18 d. Frontal cortex dopaminergic and serotoninergic neurotransmitters and phospholipid fatty acids were measured. Piglets fed the D- diet had significantly lower frontal cortex dopamine, 3,4-dihydroxyphenylacetic (DOPAC), homovanillic acid (HVA), serotonin and 5-hydroxyindoleacetic acid (5-HIAA) concentrations than did piglets fed the C- diets. Frontal cortex dopamine, norepinephrine, DOPAC, HVA, serotonin and 5-HIAA were higher in piglets fed the D+ compared to those fed the D- diet (P < 0.05) and not different between piglets fed the D+ and those fed the C- diets or the C- and C+ diets. Piglets fed the D- diet had lower frontal cortex phosphatidylcholine (PC) and phosphatidylinositol (PI) 20:4(n-6) and PC and phosphatidylethanolamine (PE) 22:6(n-3) than did piglets fed the C- diet (P < 0.05). Piglets fed the D+ diet had higher frontal cortex PC and PI 20:4(n-6) and PC, PE, PS and PI 22:6(n-3) than did piglets fed the D- diet. These studies show that dietary essential fatty acid deficiency fed for 18 d from birth affects frontal cortex neurotransmitters in rapidly growing piglets and that these changes are specifically due to 20:4(n-6) and/or 22:6(n-3).     

Changes in plasma fatty acid composition after intake of a standardised breakfast in prepubertal obese children

Obese patients typically show a pattern of dyslipidaemia and changes in plasma fatty acid composition reflecting abnormalities in lipoprotein metabolism and dietary habits. Animals and obese adults have been widely studied; however, contradictory results have been published in children. The objective was to assess changes in plasma fatty acid composition in total plasma lipids and plasma lipid fractions in obese prepubertal children compared with those of normal weight and to evaluate changes in postprandial plasma fatty acids during a 3 h period after intake of a standardised breakfast. The study was a case-control study with thirty-four obese and twenty normal-weight prepubertal children (Tanner 1). Anthropometric and metabolic variables and fatty acid concentrations were measured in plasma and its fractions. Liquid chromatography was used to separate lipid fractions and GLC to quantify fatty acids. Plasma total fatty acids (TFA), SFA, MUFA and PUFA concentrations were higher in obese than in control children. Except for 18 : 0, 18 : 3n-3, 20 : 4n-6 and n-3 PUFA, all fatty acids in TAG were also elevated in the obese group. Fatty acids 16 : 1n-7, 18 : 0, 18 : 1n-9, 20 : 2n-6, TFA and MUFA significantly decreased between the 2nd and 3rd hour in normal-weight v. obese children. The concentration of 16 : 1n-7 was positively and the proportion of 20 : 4n-6 inversely associated with a significant increase in risk of obesity. Obese prepubertal children show an altered plasma fatty acid profile and concentrations, mainly related to the TAG fatty acid profile, with a lower clearance of fatty acids v. normal-weight prepubertal children.     

Dietary canola oil: effect on the accumulation of eicosapentaenoic acid in the alkenylacyl fraction of human platelet ethanolamine phosphoglyceride

Volunteers consumed a mixed-fat diet for 6 d (Pre-exp) and then either a canola-oil-based diet (CAN) containing linolenic acid (18:3n-3) or a sunflower-oil-based diet (SUN) rich in linoleic acid (18:2n-6) for 18 d, followed by the alternative diet in a crossover design. Platelet phospholipids were analyzed for changes in fatty acid composition. Eicosapentaenoic acid (EPA) (20:5n-3) was significantly higher in alkenylacyl ethanolamine phosphoglyceride (PPE) and in total phosphatidylcholine (PC) after CAN compared with SUN and Pre-exp. The 22:5n-3 was increased in PPE after CAN above concentrations found after both SUN and Pre-exp. Lower concentrations of 20:4n-6 and 22:4n-6 were observed with CAN in PC and lower concentrations of 22:4n-6 in PPE. These results indicate that the consumption of canola oil moderately increases EPA concentrations and alters the concentrations of other n-6 and n-3 fatty acids in human platelet phospholipids.     

Total fat intake modifies plasma fatty acid composition in humans

Plasma fatty acid composition reflects dietary fatty acids. Whether the total fat content of the diet alters the fatty acid composition of plasma phospholipid, cholesteryl ester, triacylglycerol and free fatty acids is unknown. To evaluate the effects of low versus high fat diets on plasma fatty acids, a 12-wk, randomized, crossover, controlled feeding trial was conducted in healthy men and women with isoenergic low fat (20% energy) and high fat (45% energy) diets containing constant proportions of fatty acids. Ten subjects consumed one experimental diet for 28 d, their usual diet for 4 wk and the alternate experimental diet for 28 d. Endpoint measures of plasma fatty acids were determined at the end of each experimental period. The effects of the two diets were compared within subjects by analysis of variance. Plasma fatty acids (%) varied in response to total dietary fat with significantly greater total polyunsaturated fat, (n-6) and 18:2(n-6) levels in phospholipids and cholesteryl esters after high fat dietary consumption. The low fat diet was associated with significantly greater total (n-3) fatty acids, 20:5(n-3) and 22:6(n-3) levels in plasma phospholipid fatty acids and cholesteryl esters. Consumption of a low fat diet alters fatty acid patterns in a manner similar to that observed with feeding of (n-3) long-chain fatty acids. This change is likely related to decreased competition for the enzymes of elongation and desaturation, with reduced total intake of 18:2(n-6) favoring elongation and desaturation of available (n-3) fatty acids.     

High levels of the (n-6) fatty acid 4,7,10,13,16-docosapentaenoate in the retinas of rabbits are reduced by feeding dietary fish oil from birth to adult life

High levels of 4,7,10,13,16-docosapentaenoic acid [22:5(n-6)], a fatty acid usually associated with (n-3) fatty acid deficiency, have been reported in the retina of young rabbits. We studied the fatty acid composition of the rabbit retina throughout development, from birth to adult life. We also attempted to modify the fatty acid composition of the retina by the feeding of fish oil, high in docosahexaenoic acid [22:6(n-3), DHA]. Female rabbits were fed either a control or 2% fish oil diet through pregnancy and the nursing period. Weaned rabbits received the mothers' diet. In the retinas of control rabbits, 22:5(n-6) represented 3.7% of total fatty acids at birth, reached 15.1% at 9 wk and declined to 5.6% in adult rabbits. However, 22:6(n-3) increased steadily from birth onwards, from 3.8% of total fatty acids at birth to 19.6% in adults. Dietary fish oil increased the trace concentrations of long-chain (n-3) fatty acids in the milk to 10% of total fatty acids, reduced retinal 22:5(n-6) to less than or equal to 0.5% at all ages, and increased DHA to approximately 30% by 9 wk. Retinal phosphatidylethanolamine was even more sensitive to the impact of the fish oil diet, with DHA levels in newborn rabbits rising from 10% (control diet) to 43% of total fatty acids. These results demonstrated that 22:5(n-6) in the normal rabbit retina remains elevated (compared with other species) at all ages even as retinal DHA increases. The great increase of DHA in newborns whose mothers were fed fish oil suggests placental transfer of DHA and incorporation into retinal lipids.     

Alpha-linolenic acid deficiency in man: effect of ethyl linolenate on plasma and erythrocyte fatty acid composition and biosynthesis of prostanoids

Treatment of human alpha-linolenic acid deficiency (ALAD) with ethyl linolenate is reported. The patient's scaly dermatitis nearly disappeared after 5-d supplementation with 0.1 mL ethyl linolenate. Pretreatment content of various n-3 fatty acids in RBC was 0-15% of healthy controls. After 14 d of supplementation, cholesterol and triglycerides were reduced by 70% of pretreatment values, 22:5n-3 and 22:6n-3 increased three- to fourfold while 18:3n-3 and 20:5n-3 remained low, indicating a rapid elongation and desaturation of 18:3n-3 in ALAD. Urinary excretion of PGI2-M was approximately 10 times higher than in healthy control subjects, while PGI3-M excretion was low. Linolenate supplementation increased PGI2-M excretion twofold, while PGI3-M remained near detection limit. Platelet capacity to synthesize TXA2, and urinary excretion of TXB2+3-M were nearly unaffected by supplementation. The results confirm that the minimal daily requirement of alpha-linolenic acid is 0.2-0.3% of total energy.     

Effect of dietary n-3 fatty acids on weight gain and liver polar lipid fatty acid composition of fingerling channel catfish

A 10-wk experiment was conducted to determine the effect of supplementing a 5% tristearin basal diet with linoleic acid [18:2(n-6)], linolenic acid [18:3(n-3)], an n-3 highly unsaturated fatty acid (n-3 HUFA) mixture, cod liver oil, corn oil or linseed oil on growth and fatty acid composition of the liver polar lipid fraction of fingerling channel catfish (Ictalurus punctatus). The lowest weight gain was observed in fish fed the basal diet. Weight gain was improved by certain levels of supplemental n-3 fatty acids. Fish fed a diet containing 2% 18:3(n-3) grew at the same rate as fish fed a diet containing 2.5% cod liver oil plus 2.5% corn oil. The best growth rate was observed in fish fed diets containing either 5% cod liver oil or 5% linseed oil. Growth rate was depressed by supplementation with 4% 18:3(n-3) or 1.25% n-3 HUFA mix. No improvement in growth rate was observed with dietary 18:2(n-6). Dietary linolenate was converted to docosahexaenoic acid [22:6(n-3)]. The ratio of 20:3(n-9) to 22:6(n-3) of the fish showing good growth was less than 0.4. The data obtained in this experiment indicate that n-3 fatty acids are essential for channel catfish and that the 18:3(n-3) or n-3 HUFA dietary requirement is 1.0-2.0% or 0.5-0.75%, respectively.     

Effects of beef- and fish-based diets on the kinetics of n-3 fatty acid metabolism in human subjects

BACKGROUND: The quantity and type of dietary polyunsaturated fatty acids (PUFAs) can alter essential fatty acid metabolism in humans. Diets rich in 20- and 22-carbon PUFAs may inhibit desaturase expression or activity and decrease the synthesis of long-chain unsaturated fatty acids. OBJECTIVE: It was theorized that the fat content of a fish-based diet would inhibit the kinetics of the in vivo metabolism of n-3 fatty acids compared with a beef-based diet. DESIGN: A compartmental model was used to determine the coefficients of the kinetic rate constants from the plasma concentration time curves of pentadeuterated (d(5)) 18:3n-3, 20:5n-3, 22:5n-3, and 22:6n-3 of 10 subjects who subsisted on 3 diets with different long-chain PUFA contents. For 3 wk, subjects reported their food intake from their usual diets and then consumed a beef-based diet for 3 wk and then a fish-based diet for an additional 3 wk. Subjects consumed 1 g d(5)-18:3n-3 ethyl ester at weeks 3, 6, and 9. Blood was drawn over 168 h and the plasma analyzed for fatty acids. The coefficients of the kinetic constants of n-3 fatty acid metabolism and the percentage utilization of the substrates were determined. RESULTS: Across all diets, < 1% of plasma 18:3n-3 was utilized for long-chain PUFA synthesis. There was a 70% reduction in the value of the rate constant coefficient that regulated transfer of the isotope from the 22:5n-3 compartment to 22:6n-3 when the fish-based diet was compared with the beef-based diet. The turnover rate of plasma d(5)-22:6n-3 also decreased. CONCLUSIONS: The primary effect of a fish-based diet on the kinetics of n-3 metabolism involves processes that inhibit the synthesis of 22:6n-3 from 22:5n-3. These processes may involve a system of feedback control mechanisms responsive to the plasma concentration of 22:6n-3.     

Fatty acid composition of milk from genetically normotensive and hypertensive rats

To assess milk fatty acid composition in genetically normotensive (Wistar Kyoto, WKY) and spontaneously hypertensive (SH) rats, WKY and SH dams (n = 10/strain) were milked under halothane anesthesia on d 5, 13 and 21 postpartum. Milk samples of 0.5-1.0 mL were then analyzed by gas-liquid chromatography. Additional WKY and SH dams (n = 2/strain) were milked on d 5 and 21 postpartum for assessment of total milk fat. In both WKY and SH strains, the amount of 8:0 and 10:0 fatty acids increased from d 5 to 21 (p less than 0.001), whereas the quantity of 18:3(n-6), 20:3(n-9), 20:3(n-6), 22:4(n-6), 22:5(n-3) and 22:6(n-3) fatty acids declined over the same period (p less than 0.001). Milk from SH rats had higher levels of 10:0 and 20:4(n-6) fatty acids on all sampling days than did milk from WKY rats (p less than 0.001), and milk from SH rats had lower levels of 16:1(n-7), 18:1(n-9) and 18:2(n-6) fatty acids on d 13 and 21 (p less than 0.001). There were no differences in milk fat content between strains. These data suggest that genetically hypertensive rat pups obtain significantly greater amounts of 20:4(n-6) and significantly lower amounts of 18:2(n-6) fatty acids from maternal milk than do their normotensive counterparts.     

Comparison of short-term feeding of dietary linoleic and gamma-linolenic acid on plasma and liver cholesterol and fatty acids in hyperchol esterolemic rats

The present study compared the short-term effect of feeding 18:2n-6 and its metabolite, 18:3n-6 on plasma cholesterol and plasma and liver fatty acid composition. Weanling female rats were maintained on a fat-free semi-synthetic diet supplemented with 10% saturated fat, 1% cholesterol and 0.5% bile salt for 5 weeks to induce hypercholesterolemia and fatty liver. The hyper cholesterolemic rats (group H) were then switched to a steroid-free fat-free diet supplemented with either 5% linoleic acid-rich oil (group L, containing 80% 18:2n-6) or 5% gamma-linoilenic acid concentrate (group G, containing 84% 18:3n-6 and 16% 18:2n-6 ethyl esters). After 2 days on the diet, plasma cholesterol and free fatty acid levels in both groups were significantly reduced. The extent of reduction was significantly greater in group G than in group L. The concentrations of triglycerides and phospholipids in plasma were not affected but those in liver were significantly changed by the dietary manipulation (increased liver phospholipids and reduced triglycerides). Both n-6 fatty acid treatments significantly modified the fatty acid compositions in all lipid fractions — reducing the levels of monoun-saturates, and 20:3n-9, but elevating those of n-6 fatty acids. The elevations of C-20 and C-22 n-6 fatty acids were consistently greater in group G than in group L. These results indicate that gamma-linolenate in comparison with linoleate was more effectively and rapidly metabolized into long chain metabolites which might account for the difference in cholesterol-lowering ability between gamma-linolenate and linoleate.     

Efficiency of conversion of alpha-linolenic acid to long chain n-3 fatty acids in man

Alpha-linolenic acid (18:3n-3) is the major n-3 (omega 3) fatty acid in the human diet. It is derived mainly from terrestrial plant consumption and it has long been thought that its major biochemical role is as the principal precursor for long chain polyunsaturated fatty acids, of which eicosapentaenoic (20:5n-3) and docosahexaenoic acid (22:6n-3) are the most prevalent. For infants, n-3 long chain polyunsaturated fatty acids are required for rapid growth of neural tissue in the perinatal period and a nutritional supply is particularly important for development of premature infants. For adults, n-3 long chain polyunsaturated fatty acid supplementation is implicated in improving a wide range of clinical pathologies involving cardiac, kidney, and neural tissues. Studies generally agree that whole body conversion of 18:3n-3 to 22:6n-3 is below 5% in humans, and depends on the concentration of n-6 fatty acids and long chain polyunsaturated fatty acids in the diet. Complete oxidation of dietary 18:3n-3 to CO2 accounts for about 25% of 18:3n-3 in the first 24 h, reaching 60% by 7 days. Much of the remaining 18:3n-3 serves as a source of acetate for synthesis of saturates and monounsaturates, with very little stored as 18:3n-3. In term and preterm infants, studies show wide variability in the plasma kinetics of 13C n-3 long chain polyunsaturated fatty acids after 13C-18:3n-3 dosing, suggesting wide variability among human infants in the development of biosynthetic capability to convert 18:3n-3 to 22:6n3. Tracer studies show that humans of all ages can perform the conversion of 18:3n-3 to 22:6n3. Further studies are required to establish quantitatively the partitioning of dietary 18:3n-3 among metabolic pathways and the influence of other dietary components and of physiological states on these processes.     

Docosahexaenoic acid and n-6 docosapentaenoic acid supplementation alter rat skeletal muscle fatty acid composition

Background  

Docosahexaenoic acid (22:6n-3, DHA) and n-6 docosapentaenoic acid (22:5n-6, DPAn-6) are highly unsaturated fatty acids (HUFA, ≥ 20 carbons, ≥ 3 double bonds) that differ by a single carbon-carbon double bond at the Δ19 position. Membrane 22:6n-3 may support skeletal muscle function through optimal ion pump activity of sarcoplasmic reticulum and electron transport in the mitochondria. Typically n-3 fatty acid deficient feeding trials utilize linoleic acid (18:2n-6, LA) as a comparison group, possibly introducing a lower level of HUFA in addition to n-3 fatty acid deficiency. The use of 22:5n-6 as a dietary control is ideal for determining specific requirements for 22:6n-3 in various physiological processes. The incorporation of dietary 22:5n-6 into rat skeletal muscles has not been demonstrated previously. A one generation, artificial rearing model was utilized to supply 22:6n-3 and/or 22:5n-6 to rats from d2 after birth to adulthood. An n-3 fatty acid deficient, artificial milk with 18:2n-6 was supplemented with 22:6n-3 and/or 22:5n-6 resulting in four artificially reared (AR) dietary groups; AR-LA, AR-DHA, AR-DPAn-6, AR-DHA+DPAn-6. A dam reared group (DAM) was included as an additional control. Animals were sacrificed at 15 wks and soleus, white gastrocnemius and red gastrocnemius muscles were collected for fatty acid analyses.     

Changes in serum and lipoprotein fatty acids of growing rats fed protein-deficient diets with low or adequate linolenic acid concentrations.

The effects of a protein-deficient diet associated with sunflower oil [adequate in 18:2(n-6), poor in 18:3(n-3)] or soybean oil [adequate in both 18:2(n-6) and 18:3(n-3)] on lipid serum and lipoprotein compositions were studied in growing rats. Four groups of rats were fed different diets: SFC (20% casein + 5% sunflower oil); SFd (2% casein + 5% sunflower oil); SC (20% casein + 5% soybean oil); Sd (2% casein + 5% soybean oil). After 28 d, both protein-deficient groups exhibited low concentrations of protein, phospholipid, triacylglycerol and total cholesterol in serum and VLDL. Compared with rats fed 20% casein diets, those fed low protein diets had lower 18:2(n-6) and 20:4(n-6) in phospholipids of serum, VLDL and HDL2-3, and the 20:4(n-6)/18:2(n-6) ratio was twofold higher in triacylglycerols of serum and VLDL. In the SFd-fed group, 22:5(n-6) was higher than in the SFC-fed group for both triacylglycerols and phospholipids in overall lipoprotein fractions studied. In addition, the 20:3(n-9)/20:4(n-6) ratio was 0.1 in HDL2-3 phospholipids of the SFd-fed group. Sunflower oil-fed rats compared with soybean oil-fed rats had greater monounsaturated fatty acids and lower total (n-3) fatty acids in both triacylglycerols and phospholipids of serum, VLDL and HDL2-3, as well as lower total (n-6) fatty acids in serum and VLDL triacylglycerols. Apolipoproteins (apo) of VLDL were drastically depressed in rats fed protein-deficient diets, whereas apo-AI of HDL2-3 showed a particular resistance. Likewise, sunflower oil-fed rats had enhanced apo-B48 of VLDL and apo-C, apo-AII and apo-AIV of HDL2-3. The present findings show that some effects of protein malnutrition were enhanced by alpha-linolenic acid deficiency, in particular reduced (n-6) and (n-3) fatty acid bioavailability.     

Fatty acid composition of skeletal muscle reflects dietary fat composition in humans

BACKGROUND: It is still unknown whether the fatty acid composition of human skeletal muscle lipids is directly influenced by the fat composition of the diet. OBJECTIVE: We investigated whether the fatty acid composition of the diet is reflected in the fatty acid profile of skeletal muscle phospholipids and triacylglycerols. DESIGN: Thirty-two healthy adults (25 men and 7 women) included in a larger controlled, multicenter dietary study were randomly assigned to diets containing a high proportion of either saturated fatty acids (SFAs) [total fat, 36% of energy; SFAs, 18% of energy; monounsaturated fatty acids (MUFAs), 10% of energy] or MUFAs (total fat, 35% of energy; SFAs, 9% of energy; MUFAs, 19% of energy) for 3 mo. Within each diet group, there was a second random assignment to supplementation with fish oil capsules [containing 3.6 g n-3 fatty acids/d; 2.4 g eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3)] or placebo. A muscle biopsy sample was taken from the vastus lateralis muscle after the diet period. Parallel analyses of diet and supplementation effects were performed. RESULTS: The proportions of myristic (14:0), pentadecanoic (15:0), heptadecanoic (17:0), and palmitoleic (16:1n-7) acids in the skeletal muscle phospholipids were higher and the proportion of oleic acid (18:1n-9) was lower in the SFA group than in the MUFA group. The proportion of total n-3 fatty acids in the muscle phospholipids was approximately 2.5 times higher, with a 5 times higher proportion of eicosapentaenoic acid (20:5n-3), in subjects supplemented with n-3 fatty acids than in those given placebo. Similar differences were observed in the skeletal muscle triacylglycerols. CONCLUSION: The fatty acid composition of skeletal muscle lipids reflects the fatty acid composition of the diet in healthy men and women.     

Incorporation and metabolism of dietary trans isomers of linolenic acid alter the fatty acid profile of rat tissues

To study the influence on lipid metabolism and platelet aggregation of the fatty acid isomerization that occurs during heat treatment, weanling rats were fed for 8 wk a diet enriched with 5% isomerized (experimental group) or normal (control group) canola oil. Geometrical isomers of alpha-linolenic acid representing 0.2 g/100 g of the experimental diet were incorporated into liver, platelets, aorta and heart, at the expense of their cis homologue and of 18:2(n-6). The major isomer, 9c,12c,15t-18:3, was also metabolized to 5c,8c,11c,14c,17t-20:5 and to an unknown compound, found in liver, platelets and aorta, which has been identified tentatively as 7c, 10c,13c,16c,19t-22:5. The greater 20:4(n-6)/18:2(n-6) ratio in the liver, platelets and heart of the experimental group than the control group indicated an enhancement of desaturation activities. This induced a higher content of long-chain (n-6) fatty acids in the experimental group. Platelet aggregation tended to be slightly higher (P: = 0.065) in the experimental group. We conclude that 0.2 g of trans isomers of alpha-linolenic acid per 100 g of diet was sufficient to be incorporated and metabolized, thus altering the fatty acid profile of rat tissues.     

Platelet phospholipid fatty acid composition and function in vegans compared with age- and sex-matched omnivore controls.

Platelet function and phospholipid composition, plasma lipids and dietary intakes were assessed in 20 vegan subjects and 20 age- and sex-matched omnivore controls. The intakes of saturated fat were lower in the vegans and those of linoleic and linolenic acids were greater. Eicosapentaenoic and docosahexaenoic acids were absent from the diets of the vegans. Plasma total cholesterol and low-density lipoprotein concentrations were lower in the male vegan subjects and those of carotene were greater compared with their controls. The platelet phospholipids of the vegans contained higher proportions of linoleic (18:2n-6) and adrenic (22:4n-6) acids and lower proportions of arachidonic (20:4n-6), eicosapentaenoic (20:5n-3), docosapentaenoic (22:5n-3) and docosahexaenoic (22:6n-3) acids. Template bleeding times, platelet aggregation induced by adenosine diphosphate, compound U44619 and collagen were similar in both groups.