Flaxseed oil and fish-oil capsule consumption alters human red blood cell n-3 fatty acid composition: a multiple-dosing trial comparing 2 sources of n-3 fatty acid

BACKGROUND: An increase in plasma n-3 fatty acid content, particularly eicosapentaenoic acid (20:5n-3; EPA) and docosahexaenoic acid (22:6n-3; DHA), is observed after consumption of fish oil-enriched supplements. Because alpha-linolenic acid (18:3n-3; ALA) is the direct precursor of EPA and DHA, ALA-enriched supplements such as flax may have a similar effect, although this hypothesis has been challenged because of reported low conversion of ALA into DHA. OBJECTIVE: To address this question, we designed a clinical trial in which flax oil, fish-oil, and sunflower oil (placebo group) capsules were given to firefighters (n = 62), a group traditionally exposed to cardiovascular disease risk factors. DESIGN: Firefighters were randomly divided into 6 experimental groups receiving 1.2, 2.4, or 3.6 g flax oil/d; 0.6 or 1.2 g fish oil/d; or 1 g sunflower oil/d for 12 wk. Blood was drawn every 2 wk, and the total phospholipid fatty acid composition of red blood cells was determined. RESULTS: As expected, fish oil produced a rapid increase in erythrocyte DHA and total n-3 fatty acids. The consumption of either 2.4 or 3.6 g flax oil/d (in capsules) was sufficient to significantly increase erythrocyte total phospholipid ALA, EPA, and docosapentaenoic acid (22:5n-3) fatty acid content. There were no differences among groups in plasma inflammatory markers or lipid profile. CONCLUSIONS: The consumption of ALA-enriched supplements for 12 wk was sufficient to elevate erythrocyte EPA and docosapentaenoic acid content, which shows the effectiveness of ALA conversion and accretion into erythrocytes. The amounts of ALA required to obtain these effects are amounts that are easily achieved in the general population by dietary modification.     

A mixed Australian fish diet and fish-oil supplementation: impact on the plasma lipid profile of healthy men

Twelve healthy men were fed in turn three diets for 6 wk each in a 3 x 3 randomized block design: a control diet (essentially fish free), a fish diet (200 g lean Australian fish flesh/d), and the same fish-based meal but supplemented with 5 g fish oil/d. Dietary eicosapentaenoic acid [EPA, 20: 5n-3 (omega-3)] was strongly associated with erythrocyte membrane EPA (r = 0.908 at 6 wk), strengthening its value as a measure of compliance in fish and fish-oil feeding trials. On the fish diet, subjects had increased incorporation of n-3 polyunsaturated fatty acids (PUFAs) at the expense of n-6 PUFAs in their erythrocyte membranes. When the fish-based diet was supplemented with fish oil (5 g/d), there was a significant lowering of plasma triacylglycerol (-0.16 +/- 0.24 mmol/L; mean +/- SD). No change in plasma total cholesterol was detected although the fish + oil diet produced a reduction in very-low-density-lipoprotein cholesterol (-0.24 +/- 0.26 mmol/L).     

Dietary supplementation with eicosapentaenoic acid, but not with other long-chain n-3 or n-6 polyunsaturated fatty acids, decreases natural killer cell activity in healthy subjects aged >55 y

BACKGROUND: Animal studies showed that dietary flaxseed oil [rich in the n-3 polyunsaturated fatty acid alpha-linolenic acid (ALA)], evening primrose oil [rich in the n-6 polyunsaturated fatty acid gamma-linolenic acid (GLA)], and fish oil [rich in the long-chain n-3 polyunsaturated fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)] can decrease natural killer (NK) cell activity. There have been no studies of the effect on NK cell activity of adding these oils to the diet of humans. OBJECTIVE: Our objective was to determine the effect of dietary supplementation with oil blends rich in ALA, GLA, arachidonic acid (AA), DHA, or EPA plus DHA (fish oil) on the NK cell activity of human peripheral blood mononuclear cells. DESIGN: A randomized, placebo-controlled, double-blind, parallel study was conducted. Healthy subjects aged 55-75 y consumed 9 capsules/d for 12 wk; the capsules contained placebo oil (an 80:20 mix of palm and sunflower seed oils) or blends of placebo oil and oils rich in ALA, GLA, AA, DHA, or EPA plus DHA. Subjects in these groups consumed 2 g ALA, 770 mg GLA, 680 mg AA, 720 mg DHA, or 1 g EPA plus DHA (720 mg EPA + 280 mg DHA) daily, respectively. Total fat intake from the capsules was 4 g/d. RESULTS: The fatty acid composition of plasma phospholipids changed significantly in the GLA, AA, DHA, and fish oil groups. NK cell activity was not significantly affected by the placebo, ALA, GLA, AA, or DHA treatment. Fish oil caused a significant reduction (mean decline: 48%) in NK cell activity that was fully reversed by 4 wk after supplementation had ceased. CONCLUSION: A moderate amount of EPA but not of other n-6 or n-3 polyunsaturated fatty acids can decrease NK cell activity in healthy subjects.     

Blood pressure lowering in elderly subjects: a double-blind crossover study of omega-3 and omega-6 fatty acids

In 46 elderly (aged greater than or equal to 60 y) hypertensive subjects with entry systolic blood pressure (SBP) greater than or equal to 160 or diastolic blood pressure (DBP) greater than or equal to 90 mm Hg, our specific aim in a randomized, double-blind, crossover study (two 8-wk treatment periods separated by a 3-wk washout) was to compare blood pressure-lowering effects of 9 g fish oil/d [omega-3 (n-3) fatty acid] vs 9 g corn oil/d [omega-6 (n-6) fatty acid]. After a 4-wk baseline period, 22 subjects were randomly assigned to receive fish oil and 24 to receive corn oil. For both 8-wk treatments there were no between-group differences in the change in blood pressure. There was a treatment difference for standing DBP when baseline values were compared with those after treatment 2; DBP decreased by 5.1 mm Hg in the fish-oil group vs 0.72 mm Hg in the corn-oil group (P = 0.024). Within groups during the first treatment, both fish oil and corn oil lowered all four blood pressure measures (P less than 0.05); blood pressures were not further lowered during the second treatment compared with the washout period. There were no significant between-group differences in laboratory safety tests or categorical side effects. Fish oil lowered triglycerides by 0.47 mmol/L (P less than 0.001). In elderly subjects, diet plus both omega-3 and omega-6 supplements (9 g/d) safely and effectively lower SBP and DBP.     

Effect of fish oil and safflower oil in common Japanese diet on human plasma fatty acid composition

The influence of fish oil and safflower oil contained in the common Japanese diet as the main dietary polyunsaturated fatty acid source on plasma fatty acids in ten female student volunteers (21-22 years old) was investigated. The subjects were divided into two groups and fed the experimental diets for five days. The total daily fat intake in the fish diet and safflower oil diet was 54.4 g and 56.2 g, respectively, and the fat derived from fish and safflower oil was 16 g and 23 g, respectively. The proportion of linoleic acid was reduced in the plasma of subjects fed the fish diet and increased in the plasma of subjects fed the safflower oil diet. The plasma levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were significantly elevated in the fish diet group. The ratio of EPA/arachidonic acid (AA) was higher, and those of n-6/n-3 and n-9/n-3 were lower in the plasma of subjects fed the fish diet when compared to the results obtained from plasma of subjects fed the safflower oil diet. From these results, it seems likely that fish oil in the common Japanese diet is a favorable source of plasma EPA and DHA even in such short term supplementation and with such a small amount of daily consumption.     

Effects of fish-oil supplementation on myocardial fatty acids in humans

BACKGROUND: Increased fish or fish-oil consumption is associated with reduced risk of cardiac mortality, especially sudden death. This benefit putatively arises from the incorporation of the long-chain n-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) into cardiomyocyte phospholipids. OBJECTIVE: The study examined the kinetics of incorporation of n-3 fatty acids into human myocardial membrane phospholipids during supplementation with fish oil and alpha-linolenic acid-rich flaxseed oil. DESIGN: Patients with low self-reported fish intake (<1 fish meal/wk and no oil supplements) accepted for elective cardiac surgery involving cardiopulmonary bypass were randomly allocated to 1 of 6 groups: no supplement; fish oil (6 g EPA+DHA/d) for either 7, 14, or 21 d before surgery; flaxseed oil; or olive oil (both 10 mL/d for 21 d before surgery). Right atrial appendage tissue removed during surgery and blood collected at enrollment and before surgery were analyzed for phospholipid fatty acids. RESULTS: Surgery rescheduling resulted in a range of treatment times from 7 to 118 d. In the fish-oil-treated subjects, accumulation of EPA and DHA in the right atrium was curvilinear with time and reached a maximum at approximately 30 d of treatment and displaced mainly arachidonic acid. Flaxseed oil supplementation yielded a small increase in atrial EPA but not DHA, whereas olive oil did not significantly change atrial n-3 fatty acids. CONCLUSION: The results of the present study show that dietary n-3 fatty acids are rapidly incorporated into human myocardial phospholipids at the expense of arachidonic acid during high-dose fish-oil supplementation.     

Metabolism of stearidonic acid in human subjects: comparison with the metabolism of other n-3 fatty acids

BACKGROUND: For many persons who wish to obtain the health benefits provided by dietary n-3 fatty acids, daily ingestion of fish or fish oil is not a sustainable long-term approach. To increase the number of sustainable dietary options, a land-based source of n-3 fatty acids that is effective in increasing tissue concentrations of the long-chain n-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) is required. OBJECTIVE: The objective of the study was to examine the ability of dietary stearidonic acid (SDA) to increase tissue concentrations of EPA and DHA in healthy human subjects and to compare the effectiveness of SDA with that of the n-3 fatty acids alpha-linolenic acid (ALA) and EPA. DESIGN: Encapsulated SDA, ALA, or EPA was ingested daily in doses of 0.75 g and then 1.5 g for periods of 3 wk each by healthy male and postmenopausal female subjects (n = 15/group) in a double-blind, parallel-group design. RESULTS: Dietary SDA increased EPA and docosapentaenoic acid concentrations but not DHA concentrations in erythrocyte and in plasma phospholipids. The relative effectiveness of the tested dietary fatty acids in increasing tissue EPA was 1:0.3:0.07 for EPA:SDA:ALA. CONCLUSIONS: Vegetable oils containing SDA could be a dietary source of n-3 fatty acids that would be more effective in increasing tissue EPA concentrations than are current ALA-containing vegetable oils. The use of SDA-containing oils in food manufacture could provide a wide range of dietary alternatives for increasing tissue EPA concentrations.     

Effects of n-3 polyunsaturated fatty acid supplementation in pregnancy on maternal and fetal erythrocyte fatty acid composition

OBJECTIVE: The aim of this study was to assess the effects of fish oil supplementation in pregnancy on maternal erythrocyte fatty acid composition at different stages of pregnancy and in the post-partum period, and on neonatal erythrocyte fatty acid composition. DESIGN: A double-blind, randomised, placebo-controlled study. SETTING:: Subiaco, Western Australia. SUBJECTS: In all, 98 women booked for delivery at St John of God Hospital, Subiaco, were recruited from private rooms of obstetricians. In total, 83 women and their healthy full-term babies completed the study. INTERVENTION: Women received either 4 g of fish oil (n=52) (56% docosahexaenoic acid (DHA) and 28% eicosapentaenoic acid (EPA) or placebo (olive oil) (n=46) per day from 20 weeks gestation until delivery. MAIN OUTCOME MEASURES: Erythrocyte phospholipid fatty acids were measured in maternal peripheral blood at 20, 30 and 37 weeks of pregnancy and at 6 weeks post partum, and from cord blood collected at birth. RESULTS: Compared to the control group, maternal EPA and DHA were significantly higher in the fish oil group at 30 and 37 weeks gestation, and remained elevated at 6 weeks post partum (P<0.001). The proportions of n-6 polyunsaturated (arachidonic acid, 22:3n-6 and 22:4n-6) were significantly lower in the fish oil supplemented group at the same time periods (P<0.001). Similarly, the proportions of EPA and DHA were significantly higher (P<0.001), and those of n-6 polyunsaturated fatty acids arachidonic acid, 20:3n-6, 22:3n-6 and 22:4n-6 were significantly lower (P<0.001), in erythrocytes from neonates in the fish oil group, compared to those in the control group. CONCLUSION: Fish oil supplementation from 20 weeks of pregnancy until birth is an effective means of enhancing n-3 fatty acid status of both mothers and neonates. Furthermore, the changes in maternal erythrocyte fatty acid composition are retained until at least 6 weeks post partum. It is essential to assess the effects of concomitant decreases in arachidonic acid status before any dietary recommendations can be made. SPONSORSHIP: The study was supported by grants from the NH & MRC and Raine Medical Research Foundation, Australia.     

The (n-3) fatty acid dose, independent of the (n-6) to (n-3) fatty acid ratio, affects the plasma fatty acid profile of normal dogs

The purpose of this study was to determine whether the dose of (n-3) fatty acids (FA) administered, independent of the relative ratio of (n-6) to (n-3) FA in the food, influences plasma FA composition in dogs. Healthy female, geriatric beagles (7-10 y old) were fed foods containing (n-6) to (n-3) FA ratios of either 40.0:1 or 1.4:1 for 12 wk (study 1) or 36 wk (study 2). In study 3, beagles were fed food with the same 1:1 ratio of (n-6) to (n-3) FA, but with increasing concentrations of (n-6) and (n-3) FA. Plasma FA concentrations were measured after completing the feeding studies. In studies 1 and 2, dogs fed fish oil-enriched food with a high (n-3) FA concentration had higher plasma total (n-3) FA, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) concentrations and lower plasma total (n-6) FA, linoleic acid, and arachidonic acid concentrations than dogs fed corn oil-enriched food with a low (n-3) FA concentration (P < 0.001). Both inclusion of fish oil (P < 0.001) and increased food intake independent of treatment effects increased the plasma DHA (P = 0.05) concentration. Furthermore, constancy of the dose of (n-3) FA administered over long periods of time was necessary to maintain plasma levels of total (n-3) FA, EPA, and DHA. In study 3, up to certain dietary concentrations (6.3 g total (n-3) FA/kg food for DHA and 9.8 g total (n-3) FA/kg food for EPA), the dose of (n-3) FA administered, independent of the (n-6) to (n-3) FA ratio, determined the plasma (n-3) FA composition. Results from our studies indicate that approximately 175 mg DHA/(kg body weight . d) is required to attain maximum plasma levels of DHA.     

Increased n-6 polyunsaturated fatty acids do not attenuate the effects of long-chain n-3 polyunsaturated fatty acids on insulin sensitivity or triacylglycerol reduction in Indian Asians

BACKGROUND: Indian Asians in Western countries have a higher rate of coronary artery disease than do the indigenous white populations, and this higher rate may be influenced by a dietary imbalance of n-6 and n-3 polyunsaturated fatty acids (PUFAs). OBJECTIVE: The objective of the study was to test the hypothesis that a high background dietary intake of n-6 PUFA attenuates the effects of fish-oil supplementation on insulin sensitivity and associated blood lipids of the metabolic syndrome. DESIGN: Twenty-nine Indian Asian men were recruited to participate in a 12-wk dietary intervention trial. Volunteers were randomly assigned to receive either a moderate or a high n-6 PUFA diet featuring modified oils and spreads over a 6-wk period. After this 6-wk period, both groups were supplemented with 4.0 g fish oil/d (2.5 g eicosapentaenoic acid + docosahexaenoic acid) for an additional 6 wk in combination with the dietary treatment. Volunteers participated in a postprandial study and an insulin sensitivity test after the 6-wk dietary intervention and again after the fish-oil supplementation period. RESULTS: There was no significant time x treatment interaction for blood lipids or insulin action after dietary intervention with the moderate or high n-6 PUFA diets in combination with fish oil. After the 6-wk period of fish oil supplementation, fasting and postprandial plasma triacylglycerol concentrations decreased significantly. CONCLUSION: The background dietary n-6 PUFA concentration did not modulate the effect of fish-oil supplementation on blood lipids or measures of insulin sensitivity in this ethnic group.     

Docosahexaenoic acid and eicosapentaenoic acid, but not alpha-linolenic acid, suppress deoxynivalenol-induced experimental IgA nephropathy in mice

Diets enriched in the (n-3) PUFAs, docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and their precursor alpha-linolenic acid (ALA), were evaluated for efficacy in ameliorating the development of IgA nephropathy (IgAN) induced in mice by the mycotoxin deoxynivalenol (DON). The effects of DON were compared in mice that were fed for 18 wk with AIN-93G diets containing 1) 10 g/kg corn oil plus 60 g/kg oleic acid (control); 2) 10 g/kg corn oil plus 35 g/kg oleic acid and 25 g/kg DHA-enriched fish oil (DHA); 3) 10 g/kg corn oil plus 33 g/kg oleic acid and 27 g/kg EPA-enriched fish oil (EPA); and 4) 10 g/kg corn oil plus 37 g/kg oleic acid and 23 g/kg DHA + EPA (1:1) enriched fish oil (DHA + EPA). The DHA, EPA and DHA + EPA diets attenuated induction by dietary DON (10 mg/kg) of serum IgA and IgA immune complexes, kidney mesangial IgA deposition, and ex vivo IgA secretion by spleen cells. Consumption of the DHA + EPA diet for 8 wk significantly abrogated the DON-induced gene expression of interleukin (IL)-6, a requisite cytokine for DON-induced IgA nephropathy, in spleen and Peyer's patches. Finally, incorporation of ALA-containing flaxseed oil up to 60 g/kg in the AIN-93G diet did not affect DON-induced IgA dysregulation in mice. Taken together, both DHA and EPA, but not ALA, ameliorated the early stages of IgAN, and these effects might be related to a reduced capacity for IL-6 production.     

Ingestion of fish oil or a derived n-3 fatty acid concentrate containing eicosapentaenoic acid (EPA) affects fatty acid compositions of individual phospholipids of rat brain, sciatic nerve and retina

The effect of feeding redfish (Sebastes marinus or mantella) oil or a derived n-3 fatty acid concentrate containing eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on the fatty acid compositions of individual phospholipids in selected neural tissues was studied in growing male rats. Control animals were given sunflower oil in the diet for the 5-wk feeding trial. Lipid analyses revealed that EPA (20:5n-3) became significantly enriched in all phospholipid fractions (phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine and phosphatidylinositol) in the tissues studied (brain, retina and sciatic nerve) in the two n-3 fatty acid dietary groups relative to controls. Corresponding changes were also found in the 22:5n-3 contents of these tissues, whereas little or no significant elevation in DHA (22:6n-3) was found. In contrast, the percentages by weight of the n-6 fatty acids including 18:2n-6, 20:4n-6 (arachidonic acid, AA), 22:4n-6 and 22:5n-6 were generally lower in the various phospholipids/tissues of the animals given fish oil or the n-3 fatty acid concentrate; the levels of 22:5n-6 and 22:4n-6 were markedly affected in this regard. These results indicate that dietary n-3 fatty acids (as EPA plus DHA) can greatly affect the fatty acid compositions of the various membrane phospholipids in nervous tissues within a relatively short time. These biochemical alterations may be important for functional changes including altered membrane fluidity, cellular responses, ion transport and the biosyntheses of AA- and EPA-derived prostaglandins and leukotrienes.     

Dietary flavonoids increase plasma very long-chain (n-3) fatty acids in rats

Flavonoids probably contribute to the health benefits associated with the consumption of fruit and vegetables. However, the mechanisms by which they exert their effects are not fully elucidated. PUFA of the (n-3) series also have health benefits. Epidemiological and clinical studies have suggested that wine flavonoids may interact with the metabolism of (n-3) PUFA and increase their blood and cell levels. The present studies in rats were designed to assess whether flavonoids actually increase plasma levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), the main very long-chain (n-3) PUFA. Rats were fed a corn-derived anthocyanin (ACN)-rich (ACN-rich) or ACN-free diet with constant intakes of plant and marine (n-3) PUFA for 8 wk (Expt. 1). Plasma fatty acids were measured by GC. The ACN-rich diet contained ~0.24 ± 0.01 mg of ACN/g pellets. There were no significant differences between groups in the main saturated, monounsaturated, and (n-6) fatty acids. In contrast, plasma EPA and DHA were greater in the ACN-rich diet group than in the ACN-free diet group (P < 0.05). We obtained similar results in 2 subsequent experiments in which rats were administered palm oil (80 μL/d) and consumed the ACN-rich or ACN-free diet (Expt. 2) or were supplemented with fish oil (60 mg/d, providing 35 mg DHA and 12 mg EPA) and consumed the ACN-rich or ACN-free diet (Expt. 3). In both experiments, plasma EPA and DHA were significantly greater in the ACN-rich diet group. These studies demonstrate that the consumption of flavonoids increases plasma very long-chain (n-3) PUFA levels. These data confirm previous clinical and epidemiological studies and provide new insights into the health benefits of flavonoids.     

Docosahexaenoic acid is superior to eicosapentaenoic acid as the essential fatty acid for growth of grouper, Epinephelus malabaricus.

Juvenile grouper (Epinephelus malabaricus) were fed seven experimental diets, one control diet and one reference diet for 12 wk to determine the dietary requirement of grouper for docosahexaenoic (DHA) and eicosapentaenoic (EPA) acids. Each of the seven diets contained 1 g/100 g DHA and EPA in various combinations and 9 g/100 g tristearin. The control diet contained 1 g/100 g trilinolenin and trilinolein (3:1, wt/wt), and no supplemental EPA or DHA. The reference diet contained only natural oils from a mixture of cod liver oil, linseed oil and safflower oil at a ratio of 2:1:1 (wt/wt/wt). Significant differences (P < 0.05) in growth were observed among the dietary treatments but not in survival rate or relative liver weight. Only the diet with the highest DHA/EPA ratio (3:1) promoted significantly greater growth than the control diet. Purified EPA and DHA did not perform better in promoting growth than did the impure EPA and DHA oils. Enhanced growth was observed when the dietary DHA/EPA ratio was greater than 1, indicating that DHA was superior to EPA in promoting fish growth. Neutral lipid (NL) was the predominant lipid fraction (>70%) in both liver and muscle. Tissue NL/polar lipid did not differ among groups except the reference diet group that had a higher ratio (P < 0.05). DHA and EPA levels in the grouper tissues, especially muscle, were highly reflective of dietary levels of DHA and EPA, indicating that direct incorporation was likely. In addition, the 20:1(n-9), concentration in NL fractions seems to be an appropriate indicator of dietary essential fatty acid deficiency in grouper.     

n-3 fatty acids of marine origin lower systolic blood pressure and triglycerides but raise LDL cholesterol compared with n-3 and n-6 fatty acids from plants

We compared the cardiovascular risk-reduction potential of three major polyunsaturated fatty acids in a double-blind study. Thirty-three normotensive and mildly hypercholesterolemic men were randomly allocated to one of three diets supplemented with linoleic acid (14.3 g/d), alpha-linolenic acid (9.2 g/d), or eicosapentaenoic acid (EPA) plus docosahexaenoic acid (DHA) (3.4 g/d). Diets were matched to provide similar amounts of the major classes of fatty acids and cholesterol. Blood pressure and plasma lipids were measured for 6 wk after a 3-wk run-in period on the linoleic acid supplement. For the diet supplemented with EPA plus DHA compared with the linoleic acid diet systolic blood pressure fell 5.1 mm Hg (p = 0.01); plasma triglyceride and VLDL cholesterol fell by 39% (p = 0.001) and 49% (p = 0.01), respectively; and LDL cholesterol rose by 9% (p = 0.01). There were no significant changes with the diet supplemented with alpha-linolenic acid. The net effect on cardiovascular risk therefore is complex and the systolic blood pressure reduction was substantial.     

Supplementing lactating women with flaxseed oil does not increase docosahexaenoic acid in their milk

BACKGROUND: Flaxseed oil is a rich source of 18:3n-3 (alpha-linolenic acid, or ALA), which is ultimately converted to 22:6n-3 (docosahexaenoic acid, or DHA), a fatty acid important for the development of the infant brain and retina. OBJECTIVE: The objective of this study was to determine the effect of flaxseed oil supplementation on the breast-milk, plasma, and erythrocyte contents of DHA and other n-3 fatty acids in lactating women. DESIGN: Seven women took 20 g flaxseed oil (10.7 g ALA) daily for 4 wk. Breast-milk and blood samples were collected weekly before, during, and after supplementation and were analyzed for fatty acid composition. RESULTS: Breast milk, plasma, and erythrocyte ALA increased significantly over time (P < 0.001) and after 2 and 4 wk of supplementation (P < 0.05). Over time, 20:5n-3 (eicosapentaenoic acid, or EPA) increased significantly in breast milk (P = 0.004) and in plasma (P < 0.001). In addition, plasma EPA increased significantly (P < 0.05) after 2 and 4 wk of supplementation. There were significant increases over time in breast-milk 22:5n-3 (docosapentaenoic acid, or DPA) (P < 0.02), plasma DPA (P < 0.001), and erythrocyte DPA (P < 0.01). No significant changes were observed in breast-milk, plasma, or erythrocyte DHA contents after flaxseed oil supplementation. CONCLUSIONS: Dietary flaxseed oil increased the breast-milk, plasma, and erythrocyte contents of the n-3 fatty acids ALA, EPA, and DPA but had no effect on breast-milk, plasma, or erythrocyte DHA contents.     

多不饱和脂肪酸对小鼠瘦素表达的影响

目的探讨多不饱和脂肪酸(PUFAs)对瘦素表达的影响。方法使用4w龄C57BL/6J雌性小鼠,分别给予不同种类高脂饲料(18%脂肪,供能比为36%)喂养-高脂豆油饲料、高脂鱼油饲料和高脂豆油:鱼油(5:1)混合饲料,以正常饲料(6%脂肪来自豆油,供能比为12%)为对照,小鼠自由进食,喂养时间为4个月。同时进行了PUFAs对体外培养3T3-L1细胞分化的干预实验,在细胞被诱导分化D5,在培养基中分别加入油酸(OA,C18:1n-9)、花生四烯酸(AA,C20:4n-6)、二十碳五烯酸(EPA,C20:5n-3)和二十二碳六烯酸(DHA,22:6n-3,0.125mmol/L)培养12h。采用酶联免疫吸附试验(ELISA)观察小鼠血浆和细胞培养基中瘦素及瘦素受体(sOB-R)表达的变化。结果鱼油组、豆油:鱼油组以及豆油组之间血浆瘦素水平(15.97±1.41,10.37±0.98和5.81±2.95μg/L)均存在显著性差异(鱼油>豆油:鱼油>豆油);与正常对照组(14.96±6.62μg/L)比,鱼油组血浆瘦素水平未发生明显变化。血浆sOB-R水平在4组饲料之间未见显著性差异。细胞培养显示,与对照组(18.70±0.67μg/gprot)比,在培养基中加入EPA和DHA后瘦素表达量(30.19±7.11和28.18±4.87μg/gprot)明显增多;而加入OA和AA对瘦素表达(19.75±6.11和24.48±9.84μg/gprot)无影响。值得注意的是,未能检测到细胞培养基中sOB-R的表达。结论饲料PUFAs对小鼠瘦素表达具有调节功能,但鱼油n-3PUFAs和豆油n-6PUFAs的作用不同。     

Decreasing linoleic acid with constant alpha-linolenic acid in dietary fats increases (n-3) eicosapentaenoic acid in plasma phospholipids in healthy men

High linoleic acid (LA) intakes have been suggested to reduce alpha-linolenic acid [ALA, 18:3(n-3)] metabolism to eicosapentaenoic acid [EPA, 20:5(n-3)] and docosahexaenoic acid [DHA, 22:6(n-3)], and favor high arachidonic acid [ARA, 20:4(n-6)]. We used a randomized cross-over study with men (n = 22) to compare the effect of replacing vegetable oils high in LA with oils low in LA in foods, while maintaining constant ALA, for 4 wk each, on plasma (n-3) fatty acids. Nonvegetable sources of fat, except fish and seafoods, were unrestricted. We determined plasma phospholipid fatty acids at wk 0, 2, 4, 6, and 8, and triglycerides, cholesterol, serum CRP, and IL-6, and platelet aggregation at wk 0, 4, and 8. LA and ALA intakes were 3.8 +/- 0.12% and 1.0 +/- 0.05%, and 10.5 +/- 0.53% and 1.1 +/- 0.06% energy with LA:ALA ratios of 4:0 and 10:1 during the low and high LA diets, respectively. The plasma phospholipid LA was higher and EPA was lower during the high than during the low LA diet period (P < 0.001), but DHA declined over the 8-wk period (r = -0.425, P < 0.001). The plasma phospholipid ARA:EPA ratios were (mean +/- SEM) 20.7 +/- 1.52 and 12.9 +/- 1.01 after 4 wk consuming the high or low LA diets, respectively (P < 0.001); LA was inversely associated with EPA (r = -0.729, P < 0.001) but positively associated with ARA:EPA (r = 0.432, P < 0.001). LA intake did not influence ALA, ARA, DPA, DHA, or total, LDL or HDL cholesterol, CRP or IL-6, or platelet aggregation. In conclusion, high LA intakes decrease plasma phospholipid EPA and increase the ARA:EPA ratio, but do not favor higher ARA.     

Influence of fish oil on ruminal biohydrogenation of C18 unsaturated fatty acids

Dietary cis-9, trans-11-conjugated linoleic acid (CLA) is generally thought to be beneficial for human health. Fish oil added to ruminant diets increases the CLA concentration of milk and meat, an increase thought to arise from alterations in ruminal biohydrogenation of unsaturated fatty acids. To investigate the mechanism for this effect, in vitro incubations were carried out with ruminal digesta and the main biohydrogenating ruminal bacterium, Butyrivibrio fibrisolvens. Linoleic acid (LA) or alpha-linolenic acid (LNA) was incubated (1.67 g/l) with strained ruminal digesta from sheep receiving a 50:50 grass hay-concentrate ration. Adding fish oil (up to 4.17 g/l) tended to decrease the initial rate of LA (P=0.025) and LNA (P=0.137) disappearance, decreased (P<0.05) the transient accumulation of conjugated isomers of both fatty acids, and increased (P<0.05) the accumulation of trans-11-18:1. Concentrations of EPA (20:5n-3) or DHA (22:6n-3), the major fatty acids in fish oil, were low (100 mg/l or less) after incubation of fish oil with ruminal digesta. Addition of EPA or DHA (50 mg/l) to pure cultures inhibited the growth and isomerase activity of B. fibrisolvens, while fish oil had no effect. In contrast, similar concentrations of EPA and DHA had no effect on biohydrogenation of LA by mixed digesta, while the addition of LA prevented metabolism of EPA and DHA. Neither EPA nor DHA was metabolised by B. fibrisolvens in pure culture. Thus, fish oil inhibits ruminal biohydrogenation by a mechanism which can be interpreted partly, but not entirely, in terms of its effects on B. fibrisolvens.     

Flaxseed oil increases the plasma concentrations of cardioprotective (n-3) fatty acids in humans

Alpha-linolenic acid (ALA) is a major dietary (n-3) fatty acid. ALA is converted to longer-chain (n-3) PUFA, such as eicosapentaenoic acid (EPA) and possibly docosahexaenoic acid (DHA). EPA and DHA are fish-based (n-3) fatty acids that have proven cardioprotective properties. We studied the effect of daily supplementation with 3 g of ALA on the plasma concentration of long-chain (n-3) fatty acids in a predominantly African-American population with chronic illness. In a randomized, double-blind trial, 56 participants were given 3 g ALA/d from flaxseed oil capsules (n = 31) or olive oil placebo capsules (n = 25). Plasma EPA levels at 12 wk in the flaxseed oil group increased by 60%, from 24.09 +/- 16.71 to 38.56 +/- 28.92 micromol/L (P = 0.004), whereas no change occurred in the olive oil group. Plasma docosapentaenoic acid (DPA) levels in the flaxseed oil group increased by 25% from 19.94 +/- 9.22 to 27.03 +/- 17.17 micromol/L (P = 0.03) with no change in the olive oil group. Plasma DHA levels did not change in either group. This study demonstrates the efficacy of the conversion of ALA to EPA and DPA in a minority population with chronic disease. ALA may be an alternative to fish oil; however, additional clinical trials with ALA are warranted.