Differences exist in the relationships between dietary linoleic and alpha-linolenic acids and their respective long-chain metabolites

Parenteral n-3 polyunsaturated fatty acids supplementation improves postoperative recovery for patients with Crohn's disease after bowel resection: a randomized, unblinded controlled clinical trial

BACKGROUND

The postoperative inflammatory response is associated with postoperative recovery in surgery. n-3 (ω-3) polyunsaturated fatty acids have been reported to lower inflammation. The postoperative role of parenteral n-3 polyunsaturated fatty acids supplementation on outcomes in Crohn's disease after bowel resection is unclear.

OBJECTIVES

We aimed to investigate the effects of postoperative parenteral n-3 polyunsaturated fatty acids supplementation in Crohn's disease.

METHODS

A prospective randomized, unblinded controlled clinical trial was conducted for patients with Crohn's disease who underwent bowel resection between May 2019 and February 2022. Postoperative complications, complete blood count, serum biochemical values, and cytokine concentrations were compared in patients with and without parenteral n-3 polyunsaturated fatty acids supplementation for 5 d postoperatively.

RESULTS

There were 268 patients randomly assigned in the analysis, with 134 in the control group (a mix of long-chain and medium-chain fats at 1.0 g/kg/d) and 134 in the treatment group (long-chain, medium-chain, and n-3 polyunsaturated fats at 1.2 g/kg/d). Twenty-six did not complete the allocated treatment, and 8 patients were lost to follow-up. The intention-to-treat analysis and the per-protocol analysis showed that there were a significant reduction in overall complication rates (22.4% compared with 49.3%; P < 0.001 and 21.8% compared with 38.2%; P = 0.006) and postoperative stay (8.8 ± 4.5 d compared with 11.2 ± 6.8 d; P = 0.001 and 8.7 ± 4.0 d compared with 11.5 ± 7.3 d; P < 0.001) in patients with parenteral n-3 polyunsaturated fatty acids supplementation compared with patients in the control group. In the secondary outcomes, the mean ± standard deviation of interleukin (IL)-6 (17.11 ± 2.14 pg/mL compared with 30.50 ± 5.14 pg/mL; P = 0.014), IL-1β (2.01 ± 0.05 pg/mL compared with 2.24 ± 0.09 pg/mL; P = 0.019), tumor necrosis factor-α (2.09 ± 0.06 pg/mL compared with 2.29 ± 0.06 pg/mL; P = 0.029), and C-reactive protein concentrations (51.3 ± 4.2 mg/L compared with 64.4 ± 5.3 mg/L; P = 0.050) on postoperative day 5 in the treatment group were much lower than those in the control group.

CONCLUSIONS

Parenteral n-3 polyunsaturated fatty acids supplementation promotes postoperative recovery in patients with Crohn's disease following bowel resection, with fewer complications and reduced inflammatory cytokines. This trial was registered at clinicaltrials.gov as NCT03901937 at https://classic.

CLINICALTRIALS

gov/ct2/show/NCT03901937?term=NCT03901937&cond=Crohn+Disease&draw=2&rank=1.

Twelve-month Studies on Perilla Oil Intake in Japanese Adults-Possible Supplement for Mental Health

Perilla oil (PO), rich in α-linolenic acid (LNA, C18:3, ω-3), is increasingly alleged to have numerous health benefits in humans. However, the current reports detailing the effects of PO on human mental health are not adequate. Therefore, in the current investigation we compared the effects of PO or placebo treatment on the mental condition of healthy adult Japanese volunteers. At baseline and after 12 months of treatment, mental health condition was assessed using the Zung Self-Rating Depression Scale (SDS) and Apathy Scale, and serum biochemical parameters were determined. From baseline to 12 months of intervention, both SDS depression and apathy scores improved significantly in the PO-administered group. Compared to those of control group, serum norepinephrine and serotonin levels after 12 months decreased in the PO-administered group. The enhanced mental state observed in PO-subjects was accompanied by LNA level increases in erythrocyte plasma membranes. Our data demonstrate that PO intake enhances blood LNA levels and may maintain healthy mental conditions in adult subjects.

Impact of dietary precursor ALA versus preformed DHA on fatty acid profiles of eggs, liver and adipose tissue and expression of genes associated with hepatic lipid metabolism in laying hens

Dietary omega-3 polyunsaturated fatty acids (n-3 PUFA), including alpha-linolenic acid (ALA) and preformed longer chain PUFA (LCPUFA, particularly docosahexaenoic acid, DHA) differ in their egg LCPUFA enrichment efficiency. However, mechanisms leading to these differences are unclear. To this end, omega-3 PUFA contents in different lipid classes, including triacylglycerol (TAG) and total phospholipid (PL) in yolk, liver and adipose, as well as the expression of key hepatic enzymes in lipid metabolism were evaluated in laying hens in response to changes in dietary supply. Seventy Lohmann hens (n=10/treatment) consumed either a control diet (0.03% total omega-3 PUFA), or the control with supplementation (0.20%, 0.40% and 0.60% total omega-3 PUFA) from either flaxseed oil or algal product, as sources of ALA (precursor) or DHA (preformed), respectively. The study was arranged in a completely randomized design, and data were analyzed using the Proc Mixed procedure of SAS. ALA accumulated as a function of intake (P<0.0001) in total and lipid classes of yolk, liver and adipose (TAG only) for ALA- and DHA-fed hens. Unlike flaxseed oil, preformed-DHA contributed to greater (P<0.0001) accumulation of LCPUFA in yolk total PL and TAG pool, as well as adipose TAG. This may relate to elevated (P<0.0001) expression of acyl-CoA synthetase (ACSL1). No difference in hepatic EPA level in total lipids was noted between both treatment groups; EPA_liver=2.1493x-0.0064; R²=0.70, P<0.0001 (x=dietary omega-3 PUFA). The latter result may highlight the role of hepatic EPA in the regulation of LCPUFA metabolism in laying hens.

Effects of postoperative parenteral nutrition with different lipid emulsions in patients undergoing major abdominal surgery

PURPOSE

This study was designed to investigate the effects of total parenteral nutrition (PN) using different lipid emulsions in patients undergoing major abdominal surgery.

METHODS

Fifty-two patients were randomized to receive soybean oil + medium chain triglycerides (MCT) (group I), soybean oil + olive oil (group II), soybean oil + olive oil + fish oil (group III) as a lipid source. PN was started on postoperative day 1 and patients were maintained on PN for a minimum period of 4 days. Laboratory variables (CRP, prealbumin, transferrin) were measured before surgery and on postoperative days.

RESULTS

Three treatment groups were included in the study. Patients in group I received long chain triglycerides (LCT) + LCT/MCT emulsion (%75 LCT + %25 LCT/MCT); Patients in group II received olive oil based emulsion (80% olive oil + 20% soybean oil, ClinOleic); Patients in group III received fish oil in addition to olive oil based emulsion (%85 ClinOleic + %15 Omegaven; Fresenius Kabi). The following 14 parameters were assessed: body weight, CRP, prealbumin, transferrin, tumor necrosis factor-α, interleukin-6, total antioxidant status, thiobarbituric acid reactive substances, oxidized low density lipoprotein-2, complete blood cell, international normalized ratio, D-dimer, activated partially thromboplastin time, prothrombin time. All other parameters showed no differences among the groups.

CONCLUSION

The results of our trial demonstrate a potential beneficial effect of soybean oil/olive oil based lipid emulsions for use in PN regarding inflammatory response and oxidant capacity in the treatment of patients.

A systematic review of the association between fish oil supplementation and the development of asthma exacerbations

A systematic review was conducted to examine the association between fish oil supplementation and the development of asthma exacerbations. Comprehensive literature reviews of recent fish oil studies were performed to evaluate alterations in asthma surrogate markers. Additionally, the relative compositions of the fish oils used in each study were analyzed. The results of the review were inconclusive, but provide a basis for future research methods.

Regulation of polyunsaturated fatty acid biosynthesis by seaweed fucoxanthin and its metabolite in cultured hepatocytes

The effects of a seaweed carotenoid, fucoxanthin, and its physiological metabolite, fucoxanthinol, on the biosynthesis of polyunsaturated fatty acids (PUFA) were investigated using cultured rat hepatoma BRL-3A. The metabolism of α-linolenic acid (18:3n-3) was suppressed by the addition of these carotenoids, resulting in a decrease in the content of eicosapentaenoic acid (20:5n-3), which suggested a down-regulation of metabolic enzymes such as fatty acid desaturase and elongase. An increase in the content of docosahexaenoic acid (22:6n-3), as observed in previous studies in vivo, might be a buffering action to maintain the membrane fluidity. The suppressive effect of fucoxanthinol on ∆6 fatty acid desaturase was not at the level of gene expression but due to specific modifications of the protein via a ubiquitin-proteasome system. A proteomic analysis revealed several factors such as phosphatidylethanolamine-binding protein that might be involved in the observed action of fucoxanthin. These findings will contribute to studies on the elucidation of the precise molecular mechanisms underlying the regulation of PUFA biosynthesis by fucoxanthin.

Bioconversion of α-linolenic acid into n-3 long-chain polyunsaturated fatty acid in hepatocytes and ad hoc cell culture optimisation

This study aimed to establish optimal conditions for a cell culture system that would allow the measurement of 18∶3n-3 (ALA) bioconversion into n-3 long-chain polyunsaturated fatty acid (n-3 LC-PUFA), and to determine the overall pathway kinetics. Using rat hepatocytes (FaO) as model cells, it was established that a maximum 20∶5n-3 (EPA) production from 50 µM ALA initial concentration was achieved after 3 days of incubation. Next, it was established that a gradual increase in the ALA concentration from 0 up to 125µM lead to a proportional increase in EPA, without concomitant increase in further elongated or desaturated products, such as 22∶5n-3 (DPA) and 22∶6n-3 (DHA) in 3 day incubations. Of interest, ALA bioconversion products were observed in the culture medium. Therefore, in vitro experiments disregarding the medium fatty acid content are underestimating the metabolism efficiency. The novel application of the fatty acid mass balance (FAMB) method on cell culture system (cells with medium) enabled quantifying the apparent enzymatic activities for the biosynthesis of n-3 LC-PUFA. The activity of the key enzymes was estimated and showed that, under these conditions, 50% (Km) of the theoretical maximal (V_max = 3654 µmol.g⁻¹ of cell protein.hour⁻¹) Fads2 activity on ALA can be achieved with 81 µM initial ALA. Interestingly, the apparent activity of Elovl2 (20∶5n-3 elongation) was the slowest amongst other biosynthesis steps. Therefore, the possible improvement of Elovl2 activity is suggested toward a more efficient DHA production from ALA. The present study proposed and described an ad hoc optimised cell culture conditions and methodology towards achieving a reliable experimental platform, using FAMB, to assist in studying the efficiency of ALA bioconversion into n-3 LC-PUFA in vitro. The FAMB proved to be a powerful and inexpensive method to generate a detailed description of the kinetics of n-3 LC-PUFA biosynthesis enzymes activities in vitro.

Effects of perilla oil on plasma concentrations of cardioprotective (n-3) fatty acids and lipid profiles in mice

The aim of this study was to examine the effects of perilla oil as well as several vegetable oils, including flaxseed oil, canola oil, and rice bran oil on plasma levels of cardioprotective (n-3) polyunsaturated fatty acids in mice by feeding each vegetable oil for a period of eight weeks. Concentrations of docosapentaenoic acid (DHA) and eicosapentaenoic acid (EPA), fish-based (n-3) polyunsaturated fatty acids, showed an increase in the plasma of mice fed perilla and flaxseed oils compared to those of mice in the control group (P < 0.05), whereas rice bran and canola oils did not alter plasma DPA and EPA concentrations. Arachidonic acid concentration was increased by feeding rice bran oil (P < 0.05), but not canola, flaxseed, or perilla oil. In addition, oleic acid, linoleic acid, and docosahexaenoic acid concentrations were altered by feeding dietary rice bran, canola, perilla, and flaxseed oils. Findings of this study showed that perilla oil, similar to flaxseed oil, is cardioprotective and could be used as an alternative to fish oil or even flaxseed oil in animal models.

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

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

β-Lactoglobulin as a molecular carrier of linoleate: characterization and effects on intestinal epithelial cells in vitro

The dairy protein β-lactoglobulin (βlg) is known to bind hydrophobic ligands such as fatty acids. In the present work, we investigated the biological activity in vitro of linoleate once complexed to bovine βlg. Binding of linoleate (C18:2) to bovine βlg was achieved by heating at 60 °C for 30 min at pH 7.4, resulting in a linoleate/βlg molar binding stoichiometry of 1.1, 2.1, and 3.4. Two types of binding sites were determined by ITC titrations. Binding of linoleate induced the formation of covalent dimers and trimers of βlg. The LD(50) on Caco-2 cells after 24 h was 58 μM linoleate. However, cell viability was unaffected when 200 μM linoleate was presented to the Caco-2 cells as part of the βlg complex. The Caco-2 cells did not increase mRNA transcript levels of long chain fatty acid transport genes, FATP4 and FABPpm, or increase levels of the cAMP signal, in response to the presence of 50 μM linoleate alone or as part of the βlg complex. Therefore, it is proposed that βlg can act as a molecular carrier and alter the bioaccessibility of linoleate/linoleic acid.

Restriction of meat, fish, and poultry in omnivores improves mood: a pilot randomized controlled trial

Background

Omnivorous diets are high in arachidonic acid (AA) compared to vegetarian diets. Research shows that high intakes of AA promote changes in brain that can disturb mood. Omnivores who eat fish regularly increase their intakes of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), fats that oppose the negative effects of AA in vivo. In a recent cross-sectional study, omnivores reported significantly worse mood than vegetarians despite higher intakes of EPA and DHA. This study investigated the impact of restricting meat, fish, and poultry on mood.

Findings

Thirty-nine omnivores were randomly assigned to a control group consuming meat, fish, and poultry daily (OMN); a group consuming fish 3-4 times weekly but avoiding meat and poultry (FISH), or a vegetarian group avoiding meat, fish, and poultry (VEG). At baseline and after two weeks, participants completed a food frequency questionnaire, the Profile of Mood States questionnaire and the Depression Anxiety and Stress Scales. After the diet intervention, VEG participants reduced their EPA, DHA, and AA intakes, while FISH participants increased their EPA and DHA intakes. Mood scores were unchanged for OMN or FISH participants, but several mood scores for VEG participants improved significantly after two weeks.

Conclusions

Restricting meat, fish, and poultry improved some domains of short-term mood state in modern omnivores. To our knowledge, this is the first trial to examine the impact of restricting meat, fish, and poultry on mood state in omnivores.

Effect of maternally supplied n-3 and n-6 oils on the fatty acid composition and mononuclear immune cell distribution of lymphatic tissue from the gastrointestinal tract of suckling piglets

Fatty acids are essential for immune cell function. Maternal dietary fatty acid supply influences body fat composition of their offspring. As a first step to study immunonutritional interactions at an early age of pigs, four sows were fed a diet containing sunflower oil or oil from seal blubber during pregnancy and lactation. Corresponding piglets were sacrificed at three consecutive time points in the suckling period and their mesenteric lymph nodes and spleen were analysed by gas chromatography for levels of fatty acid. At the same time mononuclear cells of these organs and of the intestinal lymphoid tissue from the jejunum were isolated and subpopulations characterised by flow cytometry. Levels of fatty acids from the lymphatic organs of the piglets were significantly influenced by the maternal diet. The concentration of the fatty acids 20:5n-3, 22:5n-3 and 22:6n-3 were higher in the spleen and mesenteric lymph node of piglets suckled to sows of the test diet. Additionally, suckling time affected the levels of some long chain polyunsaturated fatty acids. Dietary effects were seen on some subpopulations including CD4-CD8alpha+ lymphocytes of the mesenteric lymph nodes and CD4+CD8alpha+ lymphocytes of the lamina propria, which were higher in the group fed seal blubber oil. The levels of CD21+ B-cells were higher in the group fed sunflower oil. The results indicate that the maternal diet and suckling time affect the fatty acid status of the investigated lymphatic tissues of piglets, but may have minor effects on the investigated lymphocyte subpopulations.

Consumption of long-chain n-3 PUFA, α-linolenic acid and fish is associated with the prevalence of chronic kidney disease

Due to the anti-inflammatory properties of PUFA, it has been suggested that they may protect against kidney damage in adults. However, relatively few epidemiological studies have examined this hypothesis in human subjects. We investigated the association between dietary intakes of PUFA (n-3, n-6 and α-linolenic acid), fish and the prevalence of chronic kidney disease (CKD). A total of 2600 Blue Mountains Eye Study (1997-9) participants aged ≥ 50 years were analysed. Dietary data were collected using a semi-quantitative FFQ, and PUFA and fish intakes were calculated. Baseline biochemistry including serum creatinine was measured. Moderate CKD was defined as an estimated glomerular filtration rate of < 60 ml/min per 1·73 m2. Participants in the highest quartile of long-chain n-3 PUFA intake had a significantly reduced likelihood of having CKD compared with those in the lowest quartile of intake (multivariable-adjusted OR 0·69, 95 % CI 0·49, 0·99). α-Linolenic acid intake was positively associated with CKD (OR, per standard deviation increase in α-linolenic acid, 1·18, 95 % CI 1·05, 1·32). Total n-3 PUFA or total n-6 PUFA were not significantly associated with CKD. The highest compared with the lowest quartile of fish consumption was associated with a reduced likelihood of CKD (OR 0·68, 95 % CI 0·48, 0·97; P for trend = 0·02). The present study shows that an increased dietary intake of long-chain n-3 PUFA and fish reduces the prevalence of CKD. Hence, a diet rich in n-3 PUFA and fish could have a role in maintaining healthy kidney function, in addition to roles of these nutrients in the prevention and modulation of other diseases.

Omega-3 fatty acids and lipoprotein associated phospholipase A(2) in healthy older adult males and females

PURPOSE

Lipoprotein associated phospholipase A(2) (Lp-PLA(2)) is a novel inflammatory factor that has been independently associated with stroke and cardiovascular disease (CVD). Omega-3 fats have been implicated in reducing inflammation associated with CVD. The aim of this study was to determine if an 8-week isocaloric diet supplemented with eicosapentaenoic acid (EPA) and docosahexaenoic (DHA) in the form of fish oil or α-linolenic acid (ALA) in the form of flaxseed oil would alter Lp-PLA(2) among healthy adults ages 50 years and older.

METHODS

Fifty-nine healthy adults (~75% female, average age 61 years) were randomized to one of three groups with equal amounts of total fat intake. All capsules contained ~1 g of fat. The control group (n = 19) consumed olive oil capsules (~11 g/day); the ALA group (n = 20) consumed flaxseed oil capsules (~11 g/day) and the EPA/DHA group (n = 20) consumed fish oil capsules (~2 g/day + 9 g/day of olive oil). Fasting blood samples were obtained before and after the 8-week intervention for determination of Lp-PLA(2) mass and activity as well as lipid values.

RESULTS

We did not find any significant changes in Lp-PLA(2) mass or activity after the intervention in any of the groups; however, change in oxidized LDL was associated with change in Lp-PLA(2) mass (r = 0.37, p < 0.01).

CONCLUSION

Supplementing the diet with omega-3 fatty acids for 8-weeks did not influence Lp-PLA(2) activity or mass among older adults; altering oxidized LDL may be necessary to see changes in Lp-PLA(2) levels.

Alpha-linolenic acid and its conversion to longer chain n-3 fatty acids: benefits for human health and a role in maintaining tissue n-3 fatty acid levels

There is little doubt regarding the essential nature of alpha-linolenic acid (ALA), yet the capacity of dietary ALA to maintain adequate tissue levels of long chain n-3 fatty acids remains quite controversial. This simple point remains highly debated despite evidence that removal of dietary ALA promotes n-3 fatty acid inadequacy, including that of docosahexaenoic acid (DHA), and that many experiments demonstrate that dietary inclusion of ALA raises n-3 tissue fatty acid content, including DHA. Herein we propose, based upon our previous work and that of others, that ALA is elongated and desaturated in a tissue-dependent manner. One important concept is to recognize that ALA, like many other fatty acids, rapidly undergoes beta-oxidation and that the carbons are conserved and reused for synthesis of other products including cholesterol and fatty acids. This process and the differences between utilization of dietary DHA or liver-derived DHA as compared to ALA have led to the dogma that ALA is not a useful fatty acid for maintaining tissue long chain n-3 fatty acids, including DHA. Herein, we propose that indeed dietary ALA is a crucial dietary source of n-3 fatty acids and its dietary inclusion is critical for maintaining tissue long chain n-3 levels.

alpha-Linolenic acid supplementation and conversion to n-3 long-chain polyunsaturated fatty acids in humans

Blood levels of polyunsaturated fatty acids (PUFA) are considered biomarkers of status. Alpha-linolenic acid, ALA, the plant omega-3, is the dietary precursor for the long-chain omega-3 PUFA eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA), and docosahexaenoic acid (DHA). Studies in normal healthy adults consuming western diets, which are rich in linoleic acid (LA), show that supplemental ALA raises EPA and DPA status in the blood and in breast milk. However, ALA or EPA dietary supplements have little effect on blood or breast milk DHA levels, whereas consumption of preformed DHA is effective in raising blood DHA levels. Addition of ALA to the diets of formula-fed infants does raise DHA, but no level of ALA tested raises DHA to levels achievable with preformed DHA at intakes similar to typical human milk DHA supply. The DHA status of infants and adults consuming preformed DHA in their diets is, on average, greater than that of people who do not consume DHA. With no other changes in diet, improvement of blood DHA status can be achieved with dietary supplements of preformed DHA, but not with supplementation of ALA, EPA, or other precursors.

Optimization of the omega-3 extraction as a functional food from flaxseed

The fatty acid content, total lipid, refractive index, peroxide, iodine, acid and saponification values of Iranian linseed oil (Linum usitatissimum) were studied. For optimization of extraction conditions, this oil was extracted by solvents (petroleum benzene and methanol-water-petroleum benzene) in 1:2, 1:3 and 1:4 ratios at 2, 5 and 8 h. Then its fatty acid content, omega-3 content and extraction yield were determined. According to the statistical analysis, petroleum benzene in a ratio of 1:3 at 5 h was chosen for the higher fatty acid, extraction yield, and economical feasibility. For preservation of omega-3 ingredients, oil with specified characters containing 46.8% omega-3 was kept under a nitrogen atmosphere at -30 degrees C during 0, 7, 30, 60 and 90 days and its peroxide value was determined. Statistical analysis showed a significant difference in the average amount of peroxide value only on the first 7 days of storage, and its increase (8.30%) conformed to the international standard.

Fatty acid composition of adipose tissue and blood in humans and its use as a biomarker of dietary intake

Accurate assessment of fat intake is essential to examine the relationships between diet and disease risk but the process of estimating individual intakes of fat quality by dietary assessment is difficult. Tissue and blood fatty acids, because they are mainly derived from the diet, have been used as biomarkers of dietary intake for a number of years. We review evidence from a wide variety of cross-sectional and intervention studies and summarise typical values for fatty acid composition in adipose tissue and blood lipids and changes that can be expected in response to varying dietary intake. Studies in which dietary intake was strictly controlled confirm that fatty acid biomarkers can complement dietary assessment methodologies and have the potential to be used more quantitatively. Factors affecting adipose tissue and blood lipid composition are discussed, such as the physical properties of triacylglycerol, total dietary fat intake and endogenous fatty acid synthesis. The relationship between plasma lipoprotein concentrations and total plasma fatty acid composition, and the use of fatty acid ratios as indices of enzyme activity are also addressed.

Lowering plasma homocysteine concentrations of older men and women with folate, vitamin B-12, and vitamin B-6 does not affect the proportion of (n-3) long chain polyunsaturated fatty acids in plasma phosphatidylcholine

There is evidence to suggest that folate, homocysteine, or both affect the (n-3) long chain PUFA composition of tissues; however, this evidence is derived largely from experiments with animals and small observational studies in humans. Results from randomized controlled trials are needed. The objective of this study was to determine whether homocysteine lowering with a B vitamin supplement affects the proportion of (n-3) long-chain PUFA in plasma phosphatidylcholine. We conducted a double-blind, placebo-controlled, randomized clinical trial involving 253 participants, 65 y or older, with plasma homocysteine concentrations of at least 13 micromol/L. Participants in the vitamin group (n = 127) took a daily supplement containing 1000 microg folate, 500 microg vitamin B-12, and 10 mg vitamin B-6 for 2 y. The fatty acid composition of plasma phosphatidylcholine was measured at baseline and at 2 y. Plasma homocysteine concentrations during the course of the study were 4.4 micromol/L lower in the vitamin group than in the placebo group. The proportions of eicosapentaenoic, docosapentaenoic, and docosahexaenoic acids in plasma phosphatidylcholine did not differ between the vitamin and placebo groups at 2 y; the mean differences after adjusting for baseline values and sex were -0.03 (99% CI: -0.22, 0.16), 0.03 (99% CI: -0.03, 0.09), and -0.02 (99% CI: -0.27, 0.24) mol%, respectively. Lowering plasma homocysteine concentrations of older men and women with folate, vitamin B-12, and vitamin B-6 had no effect on the proportion of (n-3) long-chain PUFA in plasma phosphatidylcholine.

Long-term effect of dietary α-linolenic acid or decosahexaenoic acid on incorporation of decosahexaenoic acid in membranes and its influence on rat heart in vivo

The present study was designed to evaluate whether long-term intake of dietary α-linolenic acid (ALA), supplied as whole grain-extruded linseed, can increase endogenous production of n-3 long-chain polyunsaturated fatty acids (FAs) in healthy adult rats and influence the heart rate (HR) and adrenergic response in the same way as docosahexaenoic acid (DHA)-rich diets. DHA enrichment was evaluated using FA analysis of tissue phospholipids after 8, 16, 24, and 32 wk of feeding in male Wistar rats randomly assigned to three dietary groups ( n = 8 in each group): a reference fat diet (RFD), an ALA-rich (ALA) diet, and a DHA-rich (DHA) diet. At 1 wk before the animals were killed, under anesthesia, HR was measured from ECG recordings during an adrenergic stimulation challenge ( n = 8). There was a significant increase of DHA in the cardiac membrane in the ALA group compared with the RFD group. DHA content in the cardiac membrane was ∼10% in the ALA group vs. 20% in the DHA group and 4% in the RFD group. The cardiac FA profile was established after 2 mo and remained essentially unchanged thereafter. Regardless of the diet, DHA in the heart decreased with age. Nevertheless, DHA content in the heart remained at >15% in the DHA group and remained greater in older rats fed the ALA diet than in younger RFD-fed rats. Basal HR decreased in the ALA group (395 ± 24.9 beats/min) to a level between that of the DHA and RFD groups (375 ± 26.4 and 407 ± 36.7 beats/min, respectively). Both n-3 dietary intakes contribute to enhancement of the chronotropic response to adrenergic agonist stimulation. Regulation of HR by neurohumoral mediators may be controlled by lower content of DHA, e.g., by a dietary supply of extruded linseed (ALA).

Adiponectin levels are reduced, independent of polymorphisms in the adiponectin gene, after supplementation with alpha-linolenic acid among healthy adults

Our first aim was to determine whether an isocaloric intervention using alpha-linolenic acid (ALA) in the form of flaxseed oil would alter adiponectin levels among overweight, otherwise healthy, males and females, and our second aim was to test for any potential modification of this intervention by 2 single nucleotide polymorphisms (276 and 45) in the adiponectin gene. Subjects included healthy adult males and females (approximately 81% female; average age, 38 years) with increased waist circumference (mean, 99 cm) and body mass index (mean, 30 kg/m(2)) who were free of chronic disease, not taking medications, and sedentary. Subjects met weekly with a registered dietician for 8 weeks. The control subjects (n = 27) were instructed not to alter their habitual diet and the ALA group (n = 30) was instructed to follow an enriched ALA diet by using flaxseed oil capsules (increasing ALA to 5% of total energy intake) and to lower their dietary fat consumption by a commensurate amount. Diets were analyzed using the Food Intake and Analysis System (v. 3.0, University of Texas School of Public Health, 1998). Fasting blood samples were obtained before and after the 8-week intervention. We found significant decreases (P = .02) in adiponectin (10.12 microg/mL pre, 9.23 microg/mL post) in the ALA group as compared with the control group (7.93 microg/mL pre, 8.10 microg/mL post) after the intervention. We also saw a decline in adiponectin in all genotype groups with the greatest decline among those carrying the rare T allele of single nucleotide polymorphism 276. There were no significant changes in fasting insulin, glucose, or quantitative insulin sensitivity check index values as a result of this intervention. In conclusion, this study suggests that supplementing with ALA for 8 weeks may lower adiponectin levels among healthy individuals, and this effect appears to be independent of polymorphisms in the adiponectin gene. Although the change in adiponectin in response to the omega-3 fatty acids was not accompanied by any change in glucose, insulin, or quantitative insulin sensitivity check index, long-term implications of such a decrease should be considered in future studies.

Extremely limited synthesis of long chain polyunsaturates in adults: implications for their dietary essentiality and use as supplements

There is considerable interest in the potential impact of several polyunsaturated fatty acids (PUFAs) in mitigating the significant morbidity and mortality caused by degenerative diseases of the cardiovascular system and brain. Despite this interest, confusion surrounds the extent of conversion in humans of the parent PUFA, linoleic acid or α-linolenic acid (ALA), to their respective long-chain PUFA products. As a result, there is uncertainty about the potential benefits of ALA versus eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA). Some of the confusion arises because although mammals have the necessary enzymes to make the long-chain PUFA from the parent PUFA, in vivo studies in humans show that ≈5% of ALA is converted to EPA and <0.5% of ALA is converted to DHA. Because the capacity of this pathway is very low in healthy, nonvegetarian humans, even large amounts of dietary ALA have a negligible effect on plasma DHA, an effect paralleled in the ω6 PUFA by a negligible effect of dietary linoleic acid on plasma arachidonic acid. Despite this inefficient conversion, there are potential roles in human health for ALA and EPA that could be independent of their metabolism to DHA through the desaturation – chain elongation pathway.

Competition between 24:5n-3 and ALA for Δ6 desaturase may limit the accumulation of DHA in HepG2 cell membranes

The use of Delta 6 desaturase (D6D) twice in the conversion of alpha-linolenic acid (ALA; 18:3n-3) to docosahexaenoic acid (DHA; 22:6n-3) suggests that this enzyme may play a key regulatory role in the synthesis and accumulation of DHA from ALA. We examined this using an in vitro model of fatty acid metabolism to measure the accumulation of the long-chain metabolites of ALA in HepG2 cell phospholipids. The accumulation of ALA, eicosapentaenoic acid (20:5n-3), docosapentaenoic acid (22:5n-3), and 24:5n-3 in cell phospholipids was linearly related to the concentration of supplemented ALA over the range tested (1.8-72 microM). The accumulation of the post-D6D products of 22:5n-3, 24:6n-3 and DHA, in cell phospholipids was saturated at concentrations of >18 microM ALA. Supplementation of HepG2 cells with preformed DHA revealed that, although the accumulation of DHA in cell phospholipids approached saturation, the level of DHA in cell phospholipids was significantly greater compared with the accumulation of DHA from ALA, indicating that the accumulation of DHA from ALA was not limited by incorporation. The parallel pattern of accumulation of 24:6n-3 and DHA in response to increasing concentrations of ALA suggests that the competition between 24:5n-3 and ALA for D6D may contribute to the limited accumulation of DHA in cell membranes.

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.

Inflammatory markers are not altered by an eight week dietary α-linolenic acid intervention in healthy abdominally obese adult males and females

Atherogenesis is thought to be mediated by local and/or systemic production of pro-inflammatory cytokines and omega-3 fatty acids have been implicated in reducing these inflammatory markers. The objective of this study was to determine the effect of an isocaloric diet supplemented with a plant-based dietary omega-3 fatty acid [alpha-linolenic acid (ALA)] on interleukin-6, C-reactive protein, serum amyloid A, and tumor necrosis factor-alpha. Subjects included healthy adult males and females (approximately 79% female, average age 38 years) with increased waist circumference (mean WC=99 cm) and body mass index (mean BMI=29.8 kg/m(2)) who were free of chronic disease, not taking medications, and sedentary. Control subjects (n=24) did not to alter their habitual diet and the ALA group (n=27) followed an enriched ALA diet by using flaxseed oil capsules (increasing ALA to 5% of total energy intake) and lowered their dietary fat consumption by a commensurate amount. Fasting blood samples were obtained before and after the 8-week intervention. We found no significant changes in the inflammatory factors after this 8-week dietary intervention. This study suggests there are no beneficial effects of an 8-week ALA intervention on these inflammatory factors among young, healthy, overweight/obese subjects whose inflammatory factors are not significantly elevated.

Comparison of the effects of linseed oil and different doses of fish oil on mononuclear cell function in healthy human subjects

Studies on animal and human subjects have shown that greatly increasing the amount of linseed (also known as flaxseed) oil (rich in the n−3 polyunsaturated fatty acid (PUFA) α-linolenic acid (ALNA)) or fish oil (FO; rich in the long-chain n−3 PUFA eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)) in the diet can decrease a number of markers of immune function. The immunological effects of more modest doses of n−3 PUFA in human subjects are unclear, dose–response relationships between n−3 PUFA supply and immune function have not been established and whether ALNA has the same effects as its long-chain derivatives is not known. Therefore, the objective of the present study was to determine the effect of enriching the diet with different doses of FO or with a modest dose of ALNA on a range of functional responses of human monocytes and lymphocytes. In a randomised, placebo-controlled, double-blind, parallel study, forty healthy males aged 18–39 years were randomised to receive placebo or 3·5 g ALNA/d or 0·44, 0·94 or 1·9 g (EPA+DHA)/d in capsules for 12 weeks. The EPA:DHA ratio in the FO used was 1·0:2·5. ALNA supplementation increased the proportion of EPA but not DHA in plasma phospholipids. FO supplementation decreased the proportions of linoleic acid and arachidonic acid and increased the proportions of EPA and DHA in plasma phospholipids. The interventions did not alter circulating mononuclear cell subsets or the production of tumour necrosis factor-α, interleukin (IL) 1β, IL-2, IL-4, IL-10 or interferon-γ by stimulated mononuclear cells. There was little effect of the interventions on lymphocyte proliferation. The two higher doses of FO resulted in a significant decrease in IL-6 production by stimulated mononuclear cells. It is concluded that, with the exception of IL-6 production, a modest increase in intake of either ALNA or EPA+DHA does not influence the functional activity of mononuclear cells. The threshold of EPA+DHA intake that results in decreased IL-6 production is between 0·44 and 0·94 g/d.

Effects of hempseed and flaxseed oils on the profile of serum lipids, serum total and lipoprotein lipid concentrations and haemostatic factors

BACKGROUND

Both hempseed oil (HO) and flaxseed oil (FO) contain high amounts of essential fatty acids (FAs); i.e. linoleic acid (LA, 18:2n-6) and alpha-linolenic acid (ALA, 18:3n-3), but almost in opposite ratios. An excessive intake of one essential FA over the other may interfere with the metabolism of the other while the metabolisms of LA and ALA compete for the same enzymes. It is not known whether there is a difference between n-3 and n-6 FA of plant origin in the effects on serum lipid profile.

AIM OF THE STUDY

To compare the effects of HO and FO on the profile of serum lipids and fasting concentrations of serum total and lipoprotein lipids, plasma glucose and insulin, and haemostatic factors in healthy humans.

METHODS

Fourteen healthy volunteers participated in the study. A randomised, double-blind crossover design was used. The volunteers consumed HO and FO (30 ml/day) for 4 weeks each. The periods were separated by a 4-week washout period.

RESULTS

The HO period resulted in higher proportions of both LA and gamma-linolenic acid in serum cholesteryl esters (CE) and triglycerides (TG) as compared with the FO period (P < 0.001), whereas the FO period resulted in a higher proportion of ALA in both serum CE and TG as compared with the HO period (P < 0.001). The proportion of arachidonic acid in CE was lower after the FO period than after the HO period (P < 0.05). The HO period resulted in a lower total-to-HDL cholesterol ratio compared with the FO period (P = 0.065). No significant differences were found between the periods in measured values of fasting serum total or lipoprotein lipids, plasma glucose, insulin or hemostatic factors.

CONCLUSIONS

The effects of HO and FO on the profile of serum lipids differed significantly, with only minor effects on concentrations of fasting serum total or lipoprotein lipids, and no significant changes in concentrations of plasma glucose or insulin or in haemostatic factors.

Fatty acids in serum cholesteryl esters in relation to asthma and lung function in children

BACKGROUND

Dietary fatty acid intake has been proposed to contribute to asthma development with n-6 polyunsaturated fatty acids (PUFA) having a detrimental and n-3 PUFA a protective effect.

OBJECTIVE

The aim of our analysis was to explore the relationship between fatty acid composition of serum cholesteryl esters as marker of dietary intake and prevalence of asthma, impaired lung function and bronchial hyper-responsiveness in children.

METHODS

The study population consisted of 242 girls and 284 boys aged 8-11 years, living in Munich, Germany. Data were collected by parental questionnaire, lung function measurement and skin prick test according to the International Study of Asthma and Allergies in Childhood phase II protocol. Confounder-adjusted odds ratios (OR) with 95% confidence intervals (CI) were calculated for the association between quartiles of fatty acid concentration and health outcomes with the first quartile as reference.

RESULTS

n-3 PUFA: levels of eicosapentaenoic acid were not related to asthma and impaired lung function. Linolenic acid levels were positively associated with current asthma (OR for fourth quartile 3.35, 95% CI 1.29-8.66). Forced expiratory volume in 1 s (FEV(1)) values decreased with increasing levels of linolenic acid (p for trend=0.057). n-6 PUFA: there was a strong positive association between arachidonic acid levels and current asthma (OR(4th quartile) 4.54, 1.77-11.62) and a negative association with FEV(1) (P=0.036). In contrast, linoleic acid was negatively related to current asthma (OR(4th quartile) 0.34, 0.14-0.87) and FEV(1) values increased with increasing levels of linoleic acid (P=0.022). The ratio of measured n-6 to n-3 PUFA as well as levels of palmitic and oleic acid were not consistently related to asthma or lung function.

CONCLUSION

Our data do not support the hypothesis of a protective role of n-3 PUFA. Elevated arachidonic acid levels in children with asthma may be because of a disturbed balance in the metabolism of n-6 PUFA or may be secondary to inflammation in these patients.

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.

Long-chain conversion of [13C]linoleic acid and α-linolenic acid in response to marked changes in their dietary intake in men

We studied the long-chain conversion of [U-13C]alpha-linolenic acid (ALA) and linoleic acid (LA) and responses of erythrocyte phospholipid composition to variation in the dietary ratios of 18:3n-3 (ALA) and 18:2n-6 (LA) for 12 weeks in 38 moderately hyperlipidemic men. Diets were enriched with either flaxseed oil (FXO; 17 g/day ALA, n=21) or sunflower oil (SO; 17 g/day LA, n=17). The FXO diet induced increases in phospholipid ALA (>3-fold), 20:5n-3 [eicosapentaenoic acid (EPA), >2-fold], and 22:5n-3 [docosapentaenoic acid (DPA), 50%] but no change in 22:6n-3 [docosahexanoic acid (DHA)], LA, or 20:4n-6 [arachidonic acid (AA)]. The increases in EPA and DPA but not DHA were similar to those in subjects given the SO diet enriched with 3 g of EPA plus DHA from fish oil (n=19). The SO diet induced a small increase in LA but no change in AA. Long-chain conversion of [U-13C]ALA and [U-13C]LA, calculated from peak plasma 13C concentrations after simple modeling for tracer dilution in subsets from the FXO (n=6) and SO (n=5) diets, was similar but low for the two tracers (i.e., AA, 0.2%; EPA, 0.3%; and DPA, 0.02%) and varied directly with precursor concentrations and inversely with concentrations of fatty acids of the alternative series. [13C]DHA formation was very low (<0.01%) with no dietary influences.

Arachidonic acid in adipose tissue is associated with nonfatal acute myocardial infarction in the central valley of Costa Rica

Arachidonic acid (AA), a precursor of prothrombotic eicosanoids, is potentially atherogenic, but epidemiologic data are scarce. We evaluated the hypothesis that increased AA in adipose tissue is associated with increased risk of nonfatal acute myocardial infarction (MI), and if so, whether this association is related to dietary or adipose tissue linoleic acid. We studied the association between AA and MI in 466 cases of a first nonfatal acute MI, matched on age, gender, and residence to 466 population controls. Fatty acids (FA) were assessed by GC in adipose tissue samples collected from all subjects. Odds ratios (OR) and 95% CI were calculated from multivariate conditional logistic regression models. Subjects in the highest quintile of adipose tissue AA (0.64% of total FA) had a higher risk of nonfatal acute MI than those in the lowest quintile (0.29% of total FA), after adjusting for potential confounders including (n-3) and trans FAs (OR = 1.94, 95% CI: 1.07, 3.53, P for trend = 0.026). Adipose tissue AA was not correlated with dietary AA (r = 0.07), linoleic acid (r = 0.04), or other dietary (n-6) FAs, or with adipose tissue linoleic acid (r = -0.07). These data suggest that the association between MI and adipose tissue AA is not related to dietary intake of (n-6) FAs including linoleic acid. Better understanding of the metabolic factors that increase AA in adipose tissue is urgently needed.

Dietary intake of n-3 and n-6 fatty acids and the risk of prostate cancer

BACKGROUND

Laboratory studies have shown that n-3 fatty acids inhibit and n-6 fatty acids stimulate prostate tumor growth, but whether the dietary intake of these fatty acids affects prostate cancer risk in humans remains unclear.

OBJECTIVE

We prospectively evaluated the association between intakes of alpha-linolenic (ALA; 18:3n-3), eicosapentaenoic (EPA; 20:5n-3), docosahexaenoic (DHA; 22:6n-3), linoleic (LA; 18:2n-6), and arachidonic (AA; 20:4n-6) acids and prostate cancer risk.

DESIGN

A cohort of 47 866 US men aged 40-75 y with no cancer history in 1986 was followed for 14 y.

RESULTS

During follow-up, 2965 new cases of total prostate cancer were ascertained, 448 of which were advanced prostate cancer. ALA intake was unrelated to the risk of total prostate cancer. In contrast, the multivariate relative risks (RRs) of advanced prostate cancer from comparisons of extreme quintiles of ALA from nonanimal sources and ALA from meat and dairy sources were 2.02 (95% CI: 1.35, 3.03) and 1.53 (0.88, 2.66), respectively. EPA and DHA intakes were related to lower prostate cancer risk. The multivariate RRs of total and advanced prostate cancer from comparisons of extreme quintiles of the combination of EPA and DHA were 0.89 (0.77, 1.04) and 0.74 (0.49, 1.08), respectively. LA and AA intakes were unrelated to the risk of prostate cancer. The multivariate RR of advanced prostate cancer from a comparison of extreme quintiles of the ratio of LA to ALA was 0.62 (0.45, 0.86).

CONCLUSIONS

Increased dietary intakes of ALA may increase the risk of advanced prostate cancer. In contrast, EPA and DHA intakes may reduce the risk of total and advanced prostate cancer.

Effect of altered dietary n-3 fatty acid intake upon plasma lipid fatty acid composition, conversion of [13C]alpha-linolenic acid to longer-chain fatty acids and partitioning towards beta-oxidation in older men

The effect of increased dietary intakes of alpha-linolenic acid (ALNA) or eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) for 2 months upon plasma lipid composition and capacity for conversion of ALNA to longer-chain metabolites was investigated in healthy men (52 (SD 12) years). After a 4-week baseline period when the subjects substituted a control spread, a test meal containing [U-(13)C]ALNA (700 mg) was consumed to measure conversion to EPA, docosapentaenoic acid (DPA) and DHA over 48 h. Subjects were then randomised to one of three groups for 8 weeks before repeating the tracer study: (1) continued on same intake (control, n 5); (2) increased ALNA intake (10 g/d, n 4); (3) increased EPA+DHA intake (1.5 g/d, n 5). At baseline, apparent fractional conversion of labelled ALNA was: EPA 2.80, DPA 1.20 and DHA 0.04 %. After 8 weeks on the control diet, plasma lipid composition and [(13)C]ALNA conversion remained unchanged compared with baseline. The high-ALNA diet resulted in raised plasma triacylglycerol-EPA and -DPA concentrations and phosphatidylcholine-EPA concentration, whilst [(13)C]ALNA conversion was similar to baseline. The high-(EPA+DHA) diet raised plasma phosphatidylcholine-EPA and -DHA concentrations, decreased [(13)C]ALNA conversion to EPA (2-fold) and DPA (4-fold), whilst [(13)C]ALNA conversion to DHA was unchanged. The dietary interventions did not alter partitioning of ALNA towards beta-oxidation. The present results indicate ALNA conversion was down-regulated by increased product (EPA+DHA) availability, but was not up-regulated by increased substrate (ALNA) consumption. This suggests regulation of ALNA conversion may limit the influence of variations in dietary n-3 fatty acid intake on plasma lipid compositions.

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.

Dietary alpha-linolenic acid decreases C-reactive protein, serum amyloid A and interleukin-6 in dyslipidaemic patients

BACKGROUND

Inflammation plays an important role in the pathogenesis of coronary artery disease. We examined whether dietary supplementation with alpha-linolenic acid (ALA, 18:3n-3) affects the levels of inflammatory markers in dyslipidaemic patients.

METHODS

We recruited 76 male dyslipidaemic patients (mean age=51+/-8 years) following a typical Greek diet. They were randomly assigned either to 15 ml of linseed oil (rich in ALA) per day (n=50) or to 15 ml of safflower oil (rich in linoleic acid (LA, 18:2n-6)) per day (n=26). The ratio of n-6:n-3 in linseed oil supplemented group was 1.3:1 and in safflower oil supplemented group 13.2:1. Dietary intervention lasted for 3 months. Blood lipids and C-reactive protein (CRP), serum amyloid A (SAA), and interleukin-6 (IL-6) levels were determined prior and after intervention. CRP and SAA were measured by nephelometry and IL-6 by immunoassay.

RESULTS

Dietary supplementation with ALA decreased significantly CRP, SAA and IL-6 levels. The median decrease of CRP was 38% (1.24 vs. 0.93 mg/l, P=0.0008), of SAA 23.1% (3.24 vs. 2.39 mg/l, P=0.0001) and of IL-6 10.5% (2.18 vs. 1.7 pg/ml, P=0.01). The decrease of inflammatory markers was independent of lipid changes. Dietary supplementation with LA did not affect significantly CRP, SAA and IL-6 concentrations but decreased cholesterol levels.

CONCLUSIONS

Dietary supplementation with ALA for 3 months decreases significantly CRP, SAA and IL-6 levels in dyslipidaemic patients. This anti-inflammatory effect may provide a possible additional mechanism for the beneficial effect of plant n-3 polyunsaturated fatty acids in primary and secondary prevention of coronary artery disease.

Longitudinal study of fatty acids in plasma and erythrocyte phospholipids during pregnancy

AIM

To assess the modifications of the main fatty acids (FA) in plasma and red blood cells during pregnancy.

METHODS

A longitudinal study of 36 normal pregnant women was carried out with 3 cut-off points: first trimester, second trimester and third trimester. 14 FA in plasma and erythrocyte phospholipids were measured using capillary gas chromatography. Measurements were expressed in percentages and in absolute values.

RESULTS

In plasma there was a significant increase in the proportion of saturated FA and a decrease in the proportion of long chain polyunsaturated fatty acids (PUFA) both in the omega 6 (omega 6) and omega 3 (omega 3) series. On the other hand, in erythrocyte phospholipids there was a decrease in the proportion of eicosapentaenoic acid and an increase in that of docosahexaenoic acid. In the omega 6 series, dihomo-gamma-linolenic acid increased, whereas the omega 6 docosapentaenoic acid decreased.

CONCLUSION

There was a significant decrease in the proportion of omega 3 PUFA in plasma from the first to the third trimester. Thus, it is suggested that the omega 3 PUFA intake during pregnancy should be increased in the last trimester.

Incorporation of alpha-linolenic acid and linoleic acid into human respiratory epithelial cell lines

Animal and human studies designed to examine the effects of alpha-linolenic acid (ALA) and linoleic acid (LA) supplementation on the fatty acid composition of plasma and tissues have demonstrated a marked difference in incorporation into phospholipids of these 18-carbon precursors of the long-chain polyunsaturates. Whereas tissue phospholipid levels are linearly related to dietary ALA and LA, the levels of tissue LA can be 10-fold higher than tissue ALA even when dietary levels are equivalent. There is some dispute whether this disparity is due to ALA being more rapidly metabolized to its products or substantially oxidized by the liver, or whether LA but not ALA is readily incorporated into cellular phospholipids. We examined the level of incorporation of polyunsaturated fatty acids into human respiratory epithelial cell lines (A549, 16HBE) by determining the dose-dependent incorporation of ALA and LA as free fatty acid (5-150 microg FFA/mL). Cell membrane phospholipid ALA and LA were both increased up to approximately 20-30% total fatty acids, with a concomitant decrease predominantly in monounsaturated membrane fatty acids, before significant toxicity was observed (50 microg/mL). Our data support the concept that rather than any inherent inability by human cells to incorporate ALA into membrane phospholipids, the lack of ALA content in human and animal tissues in vivo is due to the rapid metabolism or oxidation of this fatty acid in the liver.

Modulation of human immune and inflammatory responses by dietary fatty acids

I review the effects of the amount and composition of dietary fat on indices of human immune and inflammatory responses. A reduction in the amount of fat intake enhanced several indices of immune response, including lymphocyte proliferation, natural-killer-cell activity, cytokine production, and delayed-type hypersensitivity. When total fat intake was held constant, an increase in the intake of linoleic acid (18:2 omega-6) or arachidonic acid (20:4 omega-6) by healthy human volunteers did not inhibit many indices of immune response tested but did increase the production of inflammatory eicosanoids (prostaglandin E2 and leukotriene B4). Supplementation of human diets with omega-3 fatty acids reduced several aspects of neutrophil, monocyte, and lymphocyte functions, including the production of inflammatory mediators. Most of the studies have indicated reductions in these functions, with a minimum of 1.2 g/d of supplementation with eicosapentaenoic acid and docosahexaenoic acid for 6 wk. However, other studies concomitantly supplementing with 205 mg/d of vitamin E did not find inhibition of immune-cell functions, even with larger amounts and longer durations of supplementation with these fatty acids. One study reported that supplementation with docosahexaenoic acid selectively inhibits inflammatory responses without inhibiting T- and B-cell functions. Despite some discrepancies, fish oils have been used successfully in the management of several inflammatory and autoimmune diseases. The potential for the use of fish oils in the management of these diseases is tremendous, even though further studies are needed to establish safe and adequate intake levels of omega-3 fatty acids.

Short-term supplementation of low-dose gamma-linolenic acid (GLA), alpha-linolenic acid (ALA), or GLA plus ALA does not augment LCP omega 3 status of Dutch vegans to an appreciable extent

Vegans do not consume meat and fish and have therefore low intakes of long chain polyunsaturated fatty acids (LCP). They may consequently have little negative feedback inhibition from dietary LCP on conversion of alpha -linolenic acid (ALA) to the LCP omega 3 eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids. We investigated whether supplementation of nine apparently healthy vegans with 2.01 g ALA (4 ml linseed oil), 1.17 g gamma-linolenic acid (GLA) (6 ml borage oil) or their combination increases the LCP omega 3 contents of erythrocytes (RBC) and platelets (PLT), and of plasma phospholipids (PL), cholesterol esters (CE) and triglycerides (TG). The supplements changed the dietary LA/ALA ratio (in g/g) from about 13.7 (baseline) to 6.8 (linseed oil), 14.3 (borage oil) and 6.4 (linseed + borage oil), respectively. ALA or GLA given as single supplements did not increase LCP omega 3 status, but their combination augmented LCP omega 3 (in CE) and EPA (in fasting TG) to a statistically significant, but nevertheless negligible, extent. We conclude that negative feedback inhibition by dietary LCP, if any, does not play an important role in the inability to augment notably DHA status by dietary ALA. The reach of a DHA plateau already at low dietary ALA intakes suggests that dietary DHA causes a non-functional DHA surplus, or is, alternatively, important for maintaining DHA status at a functionally relevant level.