The effect of dietary fat level and quality on plasma lipoprotein lipids and plasma fatty acids in normocholesterolemic subjects

This study examined the effect on the plasma lipids and plasma phospholipid and cholesteryl ester fatty acids of changing from a typical western diet to a very low fat (VLF) vegetarian diet containing one egg/day. The effect of the addition of saturated, monounsaturated or polyunsaturated fat (PUFA) to the VLF diet was also examined. Three groups of 10 subjects (6 women, 4 men) were fed the VLF diet (10% energy as fat) for two weeks, and then in the next two weeks the dietary fat in each group was increased by 10% energy/week using butter, olive oil or safflower oil. The fat replaced dietary carbohydrate. The VLF diet reduced both the low density lipoprotein (LDL)-and high density lipoprotein (HDL)-cholesterol levels; addition of the monounsaturated fats and PUFA increased the HDL-cholesterol levels, whereas butter increased the cholesterol levels in both the LDL- and HDL-fractions. The VLF diet led to significant reductions in the proportion of linoleic acid (18∶2ω6) and eicosapentaenoic acid (20∶5ω3) and to increases in palmitoleic (16∶1), eicosatrienoic (20∶3ω6) and arachidonic acids (20∶4ω6) in both phospholipids and cholesteryl esters. Addition of butter reversed the changes seen on the VLF diet, with the exception of 16∶1, which remained elevated. Addition of olive oil resulted in a significant rise in the proportion of 18∶1 and significant decreases in all ω3 PUFA except 22∶6 compared with the usual diet. The addition of safflower oil resulted in significant increases in 18∶2 and 20∶4ω6 and significant decreases in 18∶1, 20∶5ω3 and 22∶5ω3. These results indicate that the reduction of saturated fat content of the diet (<6% dietary energy), either by reducing the total fat content of the diet or by exchanging saturated fat with unsaturated fat, reduced the total plasma cholesterol levels by approximately 12% in normocholesterolemic subjects. Although the VLF vegetarian diet reduced both LDL- and HDL-cholesterol levels, the long-term effects of VLF diets are unlikely to be deteterious since populations which habitually consume these diets have low rates of coronary heart disease. The addition of safflower oil or olive oil to a VLF diet produced favorable changes in the lipoprotein lipid profile compared with the addition of butter. The VLF diets and diets rich in butter, olive oil or safflower oil had different effects on the 20 carbon eicosanoid precursor fatty acids in the plasma. This suggests that advice on plasma lipid lowering should also take into account the effect of the diet on the fatty acid profile of the plasma lipids.     

Linoleic acid-induced fatty acid changes in platelet and aorta of the rat: Effect of age and cholesterol

The influence of age and cholesterol on polyunsaturated fatty acids (PUFa) levels was studied in young and old male Sprague-Dawley rats. Animals were fed a fat-free diet supplemented with 10% (by wt) safflower oil with or without 1% cholesterol for 8 wk. As a result of cholesterol feeding, proportions of linoleic acid (18∶2n−6) and dihomo-γ-linolenic acid (30∶3n−6) were increased and and that of arachidonic acid (20∶4n−6) was decreased in the liver and platelet phospholipids in 64-wk-old rats, suggesting inhibitory effects of cholesterol on 20∶4n−6 synthesis from 18∶2n−6. The prominent age-dependent effect on the levels of PUFA was a retention of C−22 n−3 PUFA, accompanied by decreased C−22 n−6 PUFA and increased 20∶3n−6 in the liver and platelet phospholipids. Ratio of 20∶3n−6/20∶4n−6 increased in 64-wk-old rats regardless of dietary cholesterol, suggesting depressed Δ5-desaturase with age. In aorta phospholipids, 20∶3n−6 content and 20∶3n−6/20∶4n−6 ratio increased with cholesterol supplementation, but not with age. These results suggest that changes of PUFA composition of platelet phospholipids with age are closely linked with changes in liver phospholipids. The 20∶4n−6 content in both platelet and aorta phospholipids is kept constant, despite other n−6 and n−3 PUFA being affected by age.     

Effect of dietary α-linolenic acid and its ratio to linoleic acid on platelet and plasma fatty acids and thrombogenesis

The effect of dietary α-linolenic acid (18∶3n−3) and its ratio to linoleic acid (18∶2n−6) on platelet and plasma phospholipid (PL) fatty acid patterns and prostanoid production were studied in normolipidemic men. The study consisted of two 42-d phases. Each was divided into a 6-d pre-experimental period, during which a mixed fat diet was fed, and two 18-d experimental periods, during which a mixture of sunflower and olive oil [low 18∶3n−3 content, high 18∶2/18∶3 ratio (LO-HI diet)], soybean oil (intermediate 18∶3n−3 content, intermediate 18∶2/18∶3 ratio), canola oil (intermediate 18∶3n−3 content, low 18∶2/18∶3 ratio) and a mixture of sunflower, olive and flax oil [high 18∶3n−3 content, low 18∶2/18∶3 ratio (HI-LO diet)] provided 77% of the fat (26% of the energy) in the diet. The 18∶3n−3 content and the 18∶2/18∶3 ratio of the experimental diets were: 0.8%, 27.4; 6.5%, 6.9; 6.6%, 3.0; and 13.4%, 2.7, respectively. There were appreciable differences in the fatty acid composition of platelet and plasma PLs. Nevertheless, 18∶1n−9, 18∶2n−6 and 18∶3n−3 levels in PL reflected the fatty acid composition of the diets, although very little 18∶3n−3 was incorporated into PL. Both the level of 18∶3n−3 in the diet and the 18∶2/18∶3 ratio were important in influencing the levels of longer chain n−3 fatty acid, especially 20∶5n−3, in platelet and plasma PL. Production of 6-keto-PGF_1α was significantly (P<0.05) higher following the HI-LO diet than the LO-HI diet although dietary fat source had no effect on bleeding time or thromboxane B₂ production. The present study showed that both the level of 18∶3n−3 in the diet and its ratio to 18∶2n−6 were important in influencing long-chain n−3 fatty acid levels in platelet and plasma PL and that prostanoid production coincided with the diet-induced differences in PL fatty acid patterns.     

The effects of dietary cholesterol on blood and liver polyunsaturated fatty acids and on plasma cholesterol in rats fed various types of fatty acid diet

Male rats were fed on a fat-free diet for 8 weeks and then switched to diets containing 10% hydrogenated coconut oil (HCO), safflower oil (SFO) or evening primrose oil (EPO). Half of each group was also given 1% of cholesterol in the diet. After 5 further weeks, plama, red cell and liver fatty acids were measured in the various lipid fractions. Plasma and liver cholesterol also were estimated. In almost all fractions and on all three diets, feeding cholesterol led to accumulation of the substrates of desaturation reactions and to deficits of the products of these reactions. The results were consistent with inhibition of Δ-6, Δ-5 and Δ-4 desaturation of n−6 essential fatty acids. Since the diets were deficient in n−3 fatty acids, levels were very low but were also consistent with inhibition of desaturation. In contrast, cholesterol had relatively less consistent effects on 20∶3n−9, suggesting that desaturation of n−9 fatty acids was less inhibited. Plasma cholesterol levels rose sharply in the HCO and SFO groups but not at all in the EPO group. EPO contains the product of Δ-6 desaturation, 18∶3n−6, suggesting that conversion of linoleic acid to 18∶3n−6 and possibly to further metabolites may be important for the cholesterol-lowering effect of polyunsaturates.     

Accumulation of eicosapentaenoic acid in plasma phospholipids of subjects fed canola oil

The metabolism of α-linolenic acid from canola oil was studied in eight normolipidemic men. The 42-day study was divided into three periods: a 6-day pre-experimental and two 18-day experimental. Approximately 75% of the dietary fat (28% of total energy) was provided by a mixture of fats during the pre-experimental period and either canola oil (CO) or sunflower oil (SO) during the experimental periods. The CO and SO diets were fed in a cross-over design. The ratios of linoleic to linolenic acid were 2.6∶1 and 73.9∶1 in the CO and SO diets, respectively. Dietary fat source had an effect on plasma phospholipid fatty acids: 18∶1n−9, 18∶3n−3 and 20∶5n−3 were higher (p<0.05), and 18∶2n−6 was lower in the phosphatidylcholine fraction; 18∶1n−9 was higher and 20∶4n−6 lower in the phosphatidyl-ethanolamine fraction; and 18∶1n−9 and 20∶5n−3 were higher and 20∶4n−6 and 22∶6n−3 were lower in the alkenylacyl-ethanolamine phospholipid fraction on the CO diet as compared to the SO diet. Consumption of the canola oil diet resulted in higher n−3 fatty acid levels and lower n−6 fatty acid levels in plasma phospholipids than consumption of the sunflower oil diet.     

Influence of genotype on diet-induced changes in membrane phosphatidylcholine and phosphatidylethanolamine composition of splenocytes,liver nuclear envelope and liver mitochondria

Inbred congenic mice of strains MRL/Mp-lpr/lpr (lpr/lpr) and MRL/Mp-+/+ (+/+) were fed nutritionally adequate semipurified diets containing 20% (w/w) fat and differing in linoleic acid content. Levels of linoleic acid (18∶2n−6) and arachidonic acid (20∶4n−6) in phospholipids of splenocytes, liver mitochondria and liver nuclear envelopes were determined. Membranes of lpr/lpr mice exhibited significantly lower levels of 18∶2n−6 and 20∶4n−6 in phospholipids compared with the +/+ strain. The high linoleic acid diet increased incorporation of 18∶2n−6 and 20∶4n−6 in most phospholipid fractions of these membranes. These observations indicate that genotype as well as dietary 18∶2n−6 content significantly influenced incorporation of 18∶2n−6 and 20∶4n−6 into membrane phospholipids. The results also suggest that membrane compositional abnormalities found in the lpr/lpr mice, which develop lymphoma and age faster than +/+ mice, are not restricted to the immune system but also extend to other organs. Differences observed in phospholipid fatty acid composition in splenocytes and liver subcellular membranes for mice fed diets differing in linoleic acid content suggest that the early expression of the lpr gene resulting in progression of autoimmunity may be delayed through dietary manipulation.     

High dietary 18∶3n−3 increases the 18∶3n−3 but not the 22∶6n−3 content in the whole body, brain, skin, epididymal fat pads, and muscles of suckling rat pups

The objective of this study was to test the hypothesis that increasing maternal dietary 18∶3n−3 by decreasing the 18∶2n−6/18∶3n−3 ratio will increase the 18∶3n−3 and 22∶6n−3 content of the whole body, liver, skin (epidermis, dermis, and subcutaneous tissue), epididymal fat pads, and muscles (arms and legs) of 2-wk-old rat pups. Sprague-Dawley dams at parturition were fed semipurified diets containing either a low (18∶2n−6 to 18∶3n−3 ratio of 24.7∶1) or a high (18∶2n−6 to 18∶3n−3 ratio of 1.0∶1) 18∶3n−3 fatty acid content. During the first 2 wk of life, rat pups received only their dams' milk. Fatty acid composition of the pups' stomach contents (dams' milk), whole body, brain, liver, skin, epididymal fat pads, and muscles was determined. The stomach fatty acid composition of 18∶3n−3 reflected the dams' diet. The content of 18∶3n−3 in whole body, brain, liver, skin, epididymal fat pads, and muscles was significantly (P<0.05) greater in rat pups fed the high compared with the low 18∶3n−3 fatty acid diet. The 22∶6n−3 content of the whole body, brain, skin, epididymal fat pads, and muscles was not quantitatively different in rat pups fed either the low or high 18∶3n−3 fatty acid diet. The 20∶5n−3 and 22∶5n−3 content of the whole body, skin, and epididymal fat pads was significantly increased in rat pups fed the high compared with the low 18∶3n−3 fatty acid diet. High content of 18∶3n−3 was found in the skin of rat pups fed either a low or high 18∶3n−3 fatty acid diet. These findings demonstrate that high maternal dietary 18∶3n−3 significantly increases the 18∶3n−3 but not the 22∶6n−3 content of the whole body, brain, skin, epididymal fat pads, and muscles with approximately 39 and 41% of the whole body 18∶3n−3 content being deposited in the skin of suckling rat pups fed either the low or high 18∶3n−3 diet, respectively.     

Low-fat, monounsaturate-rich diets reduce susceptibility of low density lipoproteins to peroxidation ex vivo

Oxidative modification of low density lipoprotein (LDL) plays an important role in the process of atherosclerosis. The susceptibility of LDL to oxidation and the amount of peroxidation products formed are influenced by the lipoprotein content of 18∶1 n−9, 18∶2n−6, and the 18∶2n−6/18∶1n−9 ratio, which is dependent in part on dietary fatty acids. The purpose of this study was to determine if changing from a typical American diet to a low-fat, monousaturate-rich diet (LFMR) would result in favorable alterations in the fatty acid composition and oxidative profile of LDL in hypercholesterolemic individuals. Free-living postmennopausal hypercholesterolemic women who routinely consumed a diet moderately high in total fat and total saturates (34 and 11%, respectively) followed an LFMR diet (26% fat, 6% saturated fat, and 14% monounsaturated fat) for 6 mon. Sixteen postmenopausal hypercholesterolemic women already following standard low-fat (LF) diets acted as a control for seasonal variations in serum lipids. LDL from randomly selected subjects (LF n=6, LFMR n=5) was evaluated. LFMR diets resulted in LDL with increased concentrations and percentages of 18∶1n−9, reduced 18∶2n−6/18∶1n−9 ratio, and lower percentages of 18∶2n−6. No significant changes in LDL fatty acids occurred in the LF group. Conjugated diene lag time increased in both groups during copper-induced in vitro oxidation. Only the LFMR group experienced an increase in lipid peroxide lag time and a decrease in lipid peroxide formation. The LFMR diet was well tolerated and may be of therapeutic value in the treatment of hypercholesterolemia. A portion of this material was presented earlier at the annual meeting of the American Oil Chemists' Society and in abstract form [O'Byrne, D.J., Shireman, R.B., Knauft, D. (1993) The effects of a low-fat/high oleic acid diet on lipoproteins in postmenopausal hypercholesterolemic women, INFORM 4:553,#SS7].     

Omega-3 fatty acid and cholesterol content of newly hatched chicks from α-linolenic acid enriched eggs

Egg yolk was enriched with α-linolenic acid (18∶3n−3) by feeding laying hens diets containing flax, canola or soybean seeds. Fertilized eggs were incubated and the fatty acid composition of whole body, liver, plasma, brain and the cholesterol content of plasma and liver tissue of the hatched chicks were studied. Eggs enriched with 18∶2n−6 fatty acids by feeding hens diets containing sunflower seeds were used as the controls. Feeding flax enriched (P<0.05) egg yolk and the developing progeny with 18∶3n−3, 20∶5n−3, 22∶5n−3 and 22∶6n−3. Feeding sunflower seeds resulted in an increase (P<0.05) of 18∶2n−6, 20∶4n−6, 22∶4n−6 and 22∶5n−6. The predominant polyunsaturated fatty acid of the brain was docosahexaenoic acid (22∶6n−3) which was higher (P<0.05) in the flax and canola fed group. The cholesterol content of the liver tissue was lower (P<0.05) in chicks hatched from hens fed flax seeds. This study indicates that 18∶3n−3 and 18∶2n−6 in the maternal diet are potent modulators of long-chain polyunsaturated n−3 or n−6 fatty acid and of cholesterol content in the developing progeny.     

The effect of short-term diets rich in fish, red meat, or white meat on thromboxane and prostacyclin synthesis in humans

Foods which increase tissue arachidonic acid levels have been proposed to increase thrombosis tendency, presumably through increased platelet aggregation. This study examined the effect of doubling the dietary arachidonic acid (20∶4n−6) using meat- or fish-based diets on the systemic production of prostacyclin (PGl₂) and thromboxane (TXA₂) in 29 healthy, nonsmoking adults. There were three, 3-wk low-fat dietary periods (<15% energy as fat) in which subjects consumed a vegetarian diet for 1 wk followed by 2 wk on diets containing meat or fish as sources of 20∶4n−6. Between each diet period, there was a 3-wk washout period, during which subjects returned to their normal diets. The level of 20∶4n−6 consumed during the last 2 wk of each study was approximately double the usual intake (mean 140 mg/d), while the mean eicosapentaenoic acid (20∶5n−3) content of the diets varied from 1 mg/d on the white meat diet to 70 mg/d on the red meat diet and to 847 mg/d on the fish diet. The serum phospholipid (PL) 20∶4n−6/20∶5n−3 ratios were 11∶1 on the vegetarian diet, 15∶1 on the white meat diet, 8∶1 on the red meat diet, and 2∶1 on the fish diet (P<0.001). Neither white nor red meat diets affected platelet 20∶4n−6 levels, platelet aggregation, ex vivo platelet TXB₂ production, or the systemic PGl₂ or TXA₂ production as measured by gas chromatography-mass spectrometry analysis of the excretion levels of the principal urinary metabolites 2,3-dinor-6-keto-PGF_1α (PGl₂-M) and 11-dehydro-TXB₂ (TXA₂-M), respectively. The fish diet decreased the 20∶4n−6/20∶5n−3 ratio in platelet PL from the baseline level of 45∶1 to 13∶1 (P<0.001), had no effects on platelet aggregation, but significantly decreased platelet TXB₂, production (collagen-stimulated) and TXA₂-M production, while PGl₂-M levels were unaltered. These results indicate that short-term diets which double the usual 20∶4n−6 intake using white meat (175–330 g/d) or red meat (275–530 g/d) are not associated with an increased TXA₂ production, but this does not rule out the adverse effects of 20∶4n−6 at higher levels in the diet, or for more prolonged periods. Short-term diets containing fish (100–200 g/d with 90–210 mg/d 20∶4n−6 and approximately 650–1000 mg/d 20∶5n−3) led to significant increases in platelet 20∶5n−3 levels and a decrease in the ex vivo and systemic TXA₂ production.     

Dietary n−3 FA modulate long and very long chain FA content, rhodopsin content, and rhodopsin phosphorylation in rat rod outer segment after light exposure

A previous study has shown that the long and very long chain FA (VLCFA) content of the rat retina responds to changes in dietary n−6/n−3 ratio of the fat fed (1). The present study tested whether similar changes in these FA are associated with alterations in rhodopsin content and rhodopsin phosphorylation after light treatment. Weanling rats were fed diets containing 20% (w/w, 40% energy) fat with either high (4.8%, w/w) or low (1.2%, w/w) n−3 FA. After 6 wk of feeding, half of the animals in each group were exposed to light for 48 h at 350 lx or were kept in complete darkness. In the rod outer segment, the high n−3 diet treatment increased the level of 20∶5n−3 and 22∶6n−3 and reduced the levels of 20∶4n−6 and 24∶4n−6 in PC, PE, and PS. After the feeding of a high n−3 FA diet, total n−3 pentaenoic VLCFA from C₂₄ to C₃₄ increased in PC, whereas the n−6 tetra- and pentaenoic VLCFA decreased. No changes occurred in n−3 hexaenoic VLCFA regardless of the level of 22∶6n−3 in the diet. After light exposure, animals fed a high n−3 FA diet showed reduction in 22∶6n−3 as well as in n−6 and n−3 VLCFA in PC. FFA and TG fractions contained increased levels of both 20∶4n−6 and 22∶6n−3 after light exposure. Dark-adapted rhodopsin content and rhodopsin phosphorylation in the rod outer segment of rats fed the low n−3 FA diet were higher than in animals fed a high n−3 FA diet. After light exposure, animals fed the low n−3 FA diet lost more rhodopsin compared to animals fed the high n−3 FA diet, resulting in less phosphorylation of rhodopsin. Results indicate that the FA composition, rhodopsin content, and phosphorylation in visual cells is influenced by the dietary n−3 FA fed as well as by light exposure. The results also imply that 22∶6n−3 may not be the precursor for synthesis of hexaenoic VLCFA.     

Effect of dietary docosahexaenoic acid on desaturation and uptake in vivo of isotope-labeled oleic, linoleic, and linolenic acids by male subjects

The effect of dietary docosahexaenoic acid (22∶6n−3, DHA) on the metabolism of oleic, linoleic, and linolenic acids was investigated in male subjects (n=6) confined to a metabolic unit and fed diets containing 6.5 or <0.1 g/d of DHA for 90 d. At the end of the diet period, the subjects were fed a mixture of deuterated triglycerides containing 18∶1n−9[d6], 18∶2n−6[d2], and 18∶3n−3[d4]. Blood samples were drawn at 0, 2, 4, 6, 8, 12, 24, 48, and 72 h. Methyl esters of plasma total lipids, triglycerides, phospholipids, and cholesterol esters were analyzed by gas chromatography-mass spectrometry. Chylomicron triglyceride results show that the deuterated fatty acids were equally well absorbed and diet did not influence absorption. Compared to the low-DHA diet (LO-DHA), clearance of the labeled fatty acids from chylomicron triglycerides was modestly higher for subjects fed the high DHA diet (HI-DHA). DHA supplementation significantly reduced the concentrations of most n-6[d2] and n-3[d4] long-chain fatty acid (LCFA) metabolites in plasma lipids. Accumulation of 20∶5n−3[d4] and 22∶6n−3[d4] was depressed by 76 and 88%, respectively. Accumulations of 20∶3n−6[d2] and 20∶4n−6[d2] were both decreased by 72%. No effect of diet was observed on acyltransferase selectivity or on uptake and clearance of 18∶1n−9[d6], 18∶2n−6[d2], and 18∶3n−3[d4]. The results indicate that accumulation of n−3 LCFA metabolites synthesized from 18∶3n−3 in typical U.S. diets would be reduced from about 120 to 30 mg/d by supplementation with 6.5 g/d of DHA. Accumulation of n−6 LCFA metabolites synthesized from 18∶2n−6 in U.S. diets is estimated to be reduced from about 800 to 180 mg/d. This decrease is two to three times the amount of n−6 LCFA in a typical U.S. diet. These results support the hypothesis that health benefits associated with DHA supplementation are the combined result of reduced accretion of n−6 LCFA metabolites and an increase in n−3 LCFA levels in tissue lipids.     

Dietary α-linolenic acid increases brain but not heart and liver docosahexaenoic acid levels

Fish oil-enriched diets increase n−3 FA in tissue phospholipids; however, a similar effect by plant-derived n−3 FA is poorly defined. To address this question, we determined mass changes in phospholipid FA, individual phospholipid classes, and cholesterol in the liver, heart, and brain of rats fed diets enriched in flax oil (rich in 18∶3n−3), fish oil (rich in 22∶6n−3 and 20∶5n−3), or safflower oil (rich in 18∶2n−6) for 8 wk. In the heart and liver phospholipids, 22∶6n−3 levels increased only in the fish oil group, although rats fed flax oil accumulated 20∶5n−3 and 22∶5n−3. However, in the brain, the flax and fish oil diets increased the phospholipid 22∶6n−3 mass. In all tissues, these diets decreased the 20∶4n−6 mass, although the effect was more marked in the fish oil than in the flax oil group. Although these data do not provide direct evidence for 18∶3n−3 elongation and desaturation by the brain, they demonstrate that 18∶3n−3-enriched diets reduced tissue 20∶4n−6 levels and increased cellular n−3 levels in a tissuedependent manner. We hypothesize, based on the lack of increased 22∶6n−3 but increased 18∶3n−3 in the liver and heart, that the flax oil diet increased circulating 18∶3n−3, thereby presenting tissue with this EFA for further elongation and desaturation.     

The Effects of dietary n−3/n−6 ratio on brain development in the mouse: a dose response study with long-chain n−3 fatty acids

This study examines the effects of the ratio of n−3/n−6 fatty acids (FA) on brain development in mice when longchain n−3 FA are supplied in the diet. From conception until 12 days after birth, B6D2F₁ mice were fed liquid diets, each providing 10% of energy from olive oil, and a further 10% from different combinations of free FA concentrates derived from safflower oil (18∶2n−6), and fish oil (20∶5n−3 and 22∶6n−3). The range of dietary n−3/n−6 ratios was 0,025, 0.5, 1.0, 2.0, and 4.0, with an n−6 content of greater than 1.5% of energy in all diets, and similar levels of total polyunsaturated fatty acids (PUFA). In an additional group of ratio 0.5, 18∶2n−6 was partially replaced by its δ6 desaturation product, 18∶3n−6. Biochemical analyses were conducted on 12-day-old pup brains, as well as on samples of maternal milk. No obvious effects on overall pup growth and development were observed, apart from a smaller litter size at ratio 1. Co-variance analysis indicated that increasing the n−3/n−6 ratio was associated with slightly smaller brains, relative to body weight. We found that 18∶2n−6 and 20∶5n−3 were the predominant n−6 and n−3 FA in the milk; in the brain these were 20∶4n−6 and 22∶6n−3, respectively. Increasing dietary n−3/n−6 ratios generally resulted in an increase in n−3 FA, with a corresponding decrease in n−6 FA. The n−3/n−6 ratio of the milk lipids showed a strong linear relationship with the diet, but in the brain the rate of increase tended to decrease beyond 0.5 (phosphatidylcholine, PC) and 0.25 (phosphatidylethanolamine, PE), such that there was a significant quadratic contribution to the relationship. The partial replacement of dietary 18∶2n−6 with 18∶3n−6 raised levels of 20∶4n−6 in milk, brain PC, and brain PE. These results indicate that the n−3/n−6 ratio of the phospholipids in the developing mouse brain responds maximally to maternal dietary long-chain n−3/n−6 ratios of between 0.25 and 0.5.     

Lipid metabolism and FA composition in tissues of Eurasian perch Perca fluviatilis as influenced by dietary fats

Eurasian perch, Perca fluviatilis, were fed a semipurified fat-free diet for 4 wk, followed by a 16% feeding supplementation of either olive oil (OO), safflower oil (SO), linseed oil (LO), or cod liver oil (CLO) as the only lipid source in each diet for 10 wk. Significant reductions in total lipid of tissues were observed (31.4% in viscera, 66.7% in muscle, and 74.1% in liver) after feeding the fat-free diet. The SO-, LO-, and CLO-fed fish significantly increased lipid deposition in liver and viscera compared to fish fed the OO diet; however, muscle lipid levels were not significantly affected. Large amounts of dietary 18∶1n−9 were incorporated directly into tissue lipids when fish were fed the OO diet. The LO diet significantly elevated 18∶4n−3, 20∶5n−3, 22∶5n−3, and 22∶6n−3 in the liver compared to fish fed OO or SO diets, and the n−3/n−6 ratio was 16 times that of the SO group, with significantly high desaturation and elongation products of 18∶3n−3. These results suggest that Δ6 and Δ5 desaturases are highly active in Eurasian perch, and that the enzymes at this dietary n−3/n−6 ratio favor 18∶3n−3 over 18∶2n−6 as substrate. The SO diet significantly increased 18∶3n−6, 20∶3n−6, and 22∶5n−6 in the liver and significantly decreased EPA and DHA. This indicates that desaturation enzymes were not specifically favoring n−3 over n−6 acids in perch lipid metabolism, and that these elongation and desaturation enzymes were influenced by n−3 and n−6 FA content in the diet. The present study indicates that high tissue content of DHA in the muscle of Eurasian perch was attributable to the greater ability for n−3 acid bioconversion.     

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). The results can be interpreted to indicate an inverse relationship between the amount of dietary 18∶2n−6 and incorporation of 20∶5n−3 into erythrocyte membrane phospholipids regardless of whether the major dietary n−3 fatty acid was α-linolenate (18∶3n−3) or 20∶5n−3. This interpretation is supported by theoretical calculations.     

Incorporation of n−3 fatty acids into plasma and liver lipids of rats: Importance of background dietary fat

The health benefits of long-chain n−3 PUFA (20∶5n−3 and 22∶6n−3) depend on the extent of incorporation of these FA into plasma and tissue lipids. This study aimed to investigate the effect of the background dietary fat (saturated, monounsaturated, or n−6 polyunsaturated) on the quantitative incorporation of dietary 18∶3n−3 and its elongated and desaturated products into the plasma and the liver lipids of rats. Female weanling Wistar rats (n=54) were randomly assigned to six diet groups (n=9). The fat added to the semipurified diets was tallow (SFA), tallow plus linseed oil (SFA-LNA), sunola oil (MUFA), sunola oil plus linseed oil (MUFA-LNA), sunflower oil (PUFA), or sunflower oil plus linseed oil (PUFA-LNA). At the completion of the 4-wk feeding period, quantitative FA analysis of the liver and plasma was undertaken by GC. The inclusion of linseed oil in the rat diets increased the level of 18∶3n−3, 20∶5n−3, and, to a smaller degree, 22∶6n−3 in plasma and liver lipids regardless of the background dietary fat. The extent of incorporation of 18∶3n−3, 20∶5n−3, and 22∶5n−3 followed the order SFA-LNA>MUFA-LNA>PUFA-LNA. Levels of 22∶6n−3 were increased to a similar extent regardless of the type of major fat in the rat diets. This indicates that the background diet affects the incorporation in liver and plasma FA pools of the n−3 PUFA with the exception of 22∶6n−3 and therefore the background diet has the potential to influence the already established health benefits of long-chain n−3 fatty acids.     

Influence of temperature and high dietary linoleic acid content on esterification,elongation, and desaturation of PUFA in atlantic salmon hepatocytes

The esterification, desaturation, and elongation of [1-¹⁴C]18∶3n−3, [1-¹⁴C]18∶2n−6, and [1-¹⁴C]20∶5n−3 at 5 and at 12°C were studied using cultivated hepatocytes from Atlantic salmon. The salmon were fed diets, in which 0, 50, or 100% of the supplementary fish oil had been replaced by soybean oil, for 950 day-degrees at 5 and 12°C. The endogenous percentage of 18∶2n−6 in hepatocyte lipids was 2% in cells from fish fed a diet with 100% of the supplemental lipid from fish oil, and it was slightly less than 25% in cells from fish fed the diet with 100% of the supplemental lipid from soybean oil. Furthermore, the percentages of 20∶3n−6 and 20∶4n−6 were significantly higher in hepatocytes from fish fed on soybean oil than they were in those of fish fed on fish oil. The percentages of 20∶5n−3 and 22∶6n−3, on the other hand, were lower. The endogenous levels of n−6 FA were not significantly correlated with the total amounts of radiolabeled FA esterified in hepatocyte lipids. The main radiolabeled products formed from 18∶2n−6 were 20∶2n−6 and 20∶3n−6. The level of the important eicosanoid precursor 20∶4n−6 was twice as high in hepatocyte phospholipids from fish fed the 100% soybean oil diet as it was in hepatocytes from fish fed the diet with 100% of supplemental lipid from fish oil. The main products formed from 18∶3n−3 were 20∶4n−3, 20∶5n−3, and 22∶6n−3. High levels of dietary 18∶2n−6 do allow, or even seem to increase, the production of 22∶6n−3 from 18∶3n−3 in hepatocytes. The main products formed from 20∶5n−3 were 22∶5n−3 and 22∶6n−3. The production of 22∶6n−3 from 20∶5n−3 was higher at 5°C than at 12°C. The percentage of 24∶5n−3 was higher at 5°C than it was at 12°C, as was the ratio of 24∶5 to 22∶5. These results suggest that the elongation rate of 22∶5n−3 to 24∶5n−3 is higher at the lower temperature.     

Modulation of renal injury in pcy mice by dietary fat containing n−3 fatty acids depends on the level and type of fat

Low-fat diets and diets containing n−3 fatty acids (FA) slow the progression of renal injury in the male Han:Sprague-Dawley (SPRD)-cy rat model of polycystic kidney disease. To determine whether these dietary fat effects are similar in females and in another model of renal cystic disease, in this study we used both male and female pcy mice to examine the effects of fat level and type on disease progression. Adult pcy mice were fed 4, 10, or 20 g soybean oil/100 g diet for 130 d in study 1. In study 2, weanling pcy mice were fed high or low levels of fat rich in 18∶2n−6 (corn oil, CO) 18∶3n−3 (flaxseed oil/CO 4∶1 g/g, FO), or 22∶6n−3 (algal oil/CO 4∶1 g/g, DO) for 8 wk. In adult pcy mice, low-compared with high-fat diets lowered kidney weights (2.4±0.2 vs. 3.1±0.2 g/100 g body weight, P=0.006) and serum urea nitrogen (SUN) (9.6±0.6 vs. 11.9±0.6 mmol/L, P=0.009), whereas in young pcy mice it reduced renal fibrosis volumes (0.44±0.04 vs. 0.62±0.04 mL/kg body weight, P<0.0001). FO feeding in young pcy mice mitigated the detrimental effects of high fat on fibrosis while not altering kidney size, function, and oxidative damage when compared with the CO-fed mice. In contrast, DO-compared with CO-fed mice had higher kidney weights (2.64±0.07 vs. 2.24±0.08 g/100 g body weight, P=0.005), SUN (9.4±0.57 vs. 7.0±0.62 nmol/L, P<0.0001), and cyst volumes (7.9±0.28 vs. 6.2±0.30 mL/kg body weight, P<0.0001) and similar levels of oxidative damage and fibrosis. The FA compositions of the diets were reflected in the kidneys: 18∶2n−6, 18∶3n−3, and 22∶6n−3 were the highest in the CO, FO, and DO diets, respectively. Dietary effects on kidney disease progression were similar in males and females. A low-fat diet slows progression of renal injury in male and female pcy mice, consistent with findings in the male Han:SPRD-cy rat. Dietary fat type also influenced renal injury, with flaxseed oil diets rich in 18∶3n−3 slowing early fibrosis progression compared with diets rich in 18∶2n−6 or in 22∶6n−3.     

Dietary cod liver oil decreases arachidonic acid in rat gastric mucosa and increases stress-induced gastric erosions

The purpose of this study was to examine the influence of long-term feeding of dietary fat rich in either n−3 or n−6 fatty acids on the availability of arachidonic acid (20∶4n−6) in major phospholipids of gastric mucosa in rats. Three groups of male Wistar rats were fed either a standard diet, a cod liver oil-enriched diet (10% by weight), or a corn oil-enriched diet (10% by weight) for 8 mon. Dietary cod liver oil significantly reduced the level of 20∶4n−6 in phosphatidylcholine (PC) and in phosphatidylethanolamine (PE) of gastric mucosa. The loss of 20∶4n−6 was compensated for by eicosapentaenoic acid (20∶5n−3) in PC, whereas the decrease in 20∶4n−6 in PE corresponded to the increase in three n−3 fatty acids: 20∶5n−3, docosapentaenoic acid (22∶5n−3), and docosahexaenoic acid (22∶6n−3). The level of 20∶5n−3 was higher than the level of 22∶6n−3 both in PC and PE of mucosa in rats fed cod liver oil. Diets supplemented with corn oil increased the level of 18∶2n−6 but decreased the monoene fatty acids 16∶1 and 18∶1n−7 in PC but not in PE of gastric mucosa. The 20∶4n−6 levels of both PC and PE were markedly reduced by dietary cod liver oil, to about one-third of control levels. Similar changes were also observed in the stomach wall. Gastric erosions were observed in all rats exposed to restriction stress, but this form of stress induced twice the number of erosions in rats fed fish oil compared to control rats or rats fed corn oil. We conclude that a diet rich in fish oil altered the balance between n−6 and n−3 fatty acids in major gastric mucosal phospholipids, markedly reduced the availability of 20∶4n−6, and increased the incidence of gastric erosions induced by restriction or emotional stress.