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

The effect of flaxseed oil consumtion on blood pressure among patients with metabolic syndrome and related disorders: A systematic review and meta-analysis of randomized clinical trials

We systematically reviewed randomized clinical trials (RCTs) to elucidate the overall effects of flaxseed oil consumption on blood pressure (BP) in patients with metabolic syndrome and related disorders. PubMed, Scopus, Cochrane Library, and ISI Web of Science databases were systematically searched until March 31, 2020, to find RCTs that examined the effect of flaxseed oil consumption on BP. Weighed mean difference (WMD) was pooled using a random-effects model. Standard methods were used for the assessment of heterogeneity, sensitivity analysis, and publication bias. Meta-analysis of five trials (6 arms) showed significant reductions in systolic (WMD: -3.86 mmHg, 95% CI: -7.59 to -0.13, p = .04) BP (SBP) after flaxseed oil consumption. However, the overall effect illustrated no significant change in diastolic (WMD: -1.71 mmHg, 95% CI: -3.67 to 0.26, p = .09) BP (DBP) in the intervention group compared with the control group. Our findings revealed that flaxseed oil consumption has favorable effects on SBP in patients with metabolic syndrome and related disorders. However, further investigations are needed to provide more reliable evidence.

Omega-3 Polyunsaturated Fatty Acids Intake and Blood Pressure: A Dose-Response Meta-Analysis of Randomized Controlled Trials

Background Current evidence might support the use of omega-3 fatty acids (preferably docosahexaenoic acid and eicosapentaenoic acid) for lowering blood pressure (BP), but the strength and shape of the dose-response relationship remains unclear. Methods and Results This study included randomized controlled trials published before May 7, 2021, that involved participants aged ≥18 years, and examined an association between omega-3 fatty acids (docosahexaenoic acid, eicosapentaenoic acid, or both) and BP. A random-effects 1-stage cubic spline regression model was used to predict the average dose-response association between daily omega-3 fatty acid intake and changes in BP. We also conducted stratified analyses to examine differences by prespecified subgroups. Seventy-one trials were included, involving 4973 individuals with a combined docosahexaenoic acid+eicosapentaenoic acid dose of 2.8 g/d (interquartile range, 1.3 g/d to 3.6 g/d). A nonlinear association was found overall or in most subgroups, depicted as J-shaped dose-response curves. The optimal intake in both systolic BP and diastolic BP reductions (mm Hg) were obtained by moderate doses between 2 g/d (systolic BP, -2.61 [95% CI, -3.57 to -1.65]; diastolic BP, -1.64 [95% CI, -2.29 to -0.99]) and 3 g/d (systolic BP, -2.61 [95% CI, -3.52 to -1.69]; diastolic BP, -1.80 [95% CI, -2.38 to -1.23]). Subgroup studies revealed stronger and approximately linear dose-response relations among hypertensive, hyperlipidemic, and older populations. Conclusions This dose-response meta-analysis demonstrates that the optimal combined intake of omega-3 fatty acids for BP lowering is likely between 2 g/d and 3 g/d. Doses of omega-3 fatty acid intake above the recommended 3 g/d may be associated with additional benefits in lowering BP among groups at high risk for cardiovascular diseases.

Leukocyte Activation and Antioxidative Defense Are Interrelated and Moderately Modified by n-3 Polyunsaturated Fatty Acid-Enriched Eggs Consumption-Double-Blind Controlled Randomized Clinical Study

This placebo-controlled, double-blind, randomized, interventional study investigated the effects of low/intermediate doses of n-3 polyunsaturated fatty acids (PUFAs) on the endothelial function, markers of leukocyte activation, and oxidative status following dietary intake of n-3 PUFA-enriched hen eggs in young healthy individuals. Twenty young healthy adults of both sexes who consumed n-3 PUFA-enriched hen eggs (two eggs per day, for three weeks, total of approximately 407 mg/day n-3 PUFAs) or regular eggs (two eggs per day for three weeks, total of approximately 75 mg/day n-3 PUFAs) participated in this study. Skin microvascular endothelium-independent and endothelium-dependent vasodilation were assessed by laser Doppler flowmetry. Serum lipid profile and content of free fatty acids, markers of leukocyte activation, biochemical parameters of oxidative stress, as well as antioxidative enzymes serum activity were measured before and after respective dietary protocol. The results of this study revealed significant differences in the markers of leukocyte activation (such as CD11a/LFA-1) and antioxidative defense, which are related to increased intake of n-3 PUFAs, providing the evidence that consumption of nutritionally enriched hen eggs may affect physiological processes related to oxidative balance. The absence of significant changes in microvascular reactivity following supplementation with a low-intermediate dose of n-3 PUFAs, unlike in our previous studies where functional eggs contained ~1 g of n-3 PUFA, suggests the existence of a dose-dependent effect.

Anti-Inflammatory Potential of n-3 Polyunsaturated Fatty Acids Enriched Hen Eggs Consumption in Improving Microvascular Endothelial Function of Healthy Individuals-Clinical Trial

The effects of consumption of n-3 polyunsaturated fatty acids (n-3 PUFAs) enriched hen eggs on endothelium-dependent and endothelium-independent vasodilation in microcirculation, and on endothelial activation and inflammation were determined in young healthy individuals. Control group (N = 21) ate three regular hen eggs/daily (249 mg n-3 PUFAs/day), and n-3 PUFAs group (N = 19) ate three n-3 PUFAs enriched hen eggs/daily (1053 g n-3 PUFAs/day) for 3 weeks. Skin microvascular blood flow in response to iontophoresis of acetylcholine (AChID; endothelium-dependent) and sodium nitroprusside (SNPID; endothelium-independent) was assessed by laser Doppler flowmetry. Blood pressure (BP), body composition, body fluid status, serum lipid and free fatty acids profile, and inflammatory and endothelial activation markers were measured before and after respective dietary protocol. Results: Serum n-3 PUFAs concentration significantly increased, AChID significantly improved, and SNPID remained unchanged in n-3 PUFAs group, while none was changed in Control group. Interferon-γ (pro-inflammatory) significantly decreased and interleukin-10 (anti-inflammatory) significantly increased in n-3 PUFAs. BP, fat free mass, and total body water significantly decreased, while fat mass, interleukin-17A (pro-inflammatory), interleukin-10 and vascular endothelial growth factor A significantly increased in the Control group. Other measured parameters remained unchanged in both groups. Favorable anti-inflammatory properties of n-3 PUFAs consumption potentially contribute to the improvement of microvascular endothelium-dependent vasodilation in healthy individuals.

Flaxseed and Its Components in Treatment of Hyperlipidemia and Cardiovascular Disease

This paper describes the effects of flaxseed and its components (flax oil, secoisolariciresinoldiglucoside[SDG], flax lignan complex [FLC], and flax fibers] on serum lipids (total cholesterol [TC], low-density lipoprotein-cholesterol [LDL-C], high-density lipoprotein cholesterol [HDL-C], and triglycerides [TG]) in animals and humans. Ordinary flaxseed reduces TG, TC, LDL-C, and TC/HDL-C levels in a dose-dependent manner in animals. In humans, it reduces serum lipids in hypercholesterolemicpatients but has no effects in normocholesterolemicpatients. Flax oil has variable effects on serum lipids in normo- and hypercholesterolemic animals. Flax oil treatment, with a dosage containing greater than 25 g/day of α-linolenic acid, reduces serum lipids in humans. Although FLC reduces serum lipids and raises serum HDL-C in animals, its effects on serum lipids in humans are small and variable. Flax fibers exert small effects on serum lipids in humans. Crop Development Centre (CDC)-flaxseed, which contains low concentrations of α-linolenic acid, has significant lipid lowering effects in animals. Pure SDG has potent hypolipidemic effects and raises HDL-C. In conclusion, flaxseed and pure SDG have significant lipid-lowering effects in animals and humans, while other components of flaxseed have small and variable effects.

Effects of eicosapentaenoic acid and docosahexaenoic acid versus α-linolenic acid supplementation on cardiometabolic risk factors: a meta-analysis of randomized controlled trials

Previous randomized controlled trials (RCTs) made direct comparisons between EPA/DHA versus ALA on improving cardiovascular risk factors and have reached inconsistent findings. The aim of this meta-analysis was to compare the effects of EPA/DHA vs. ALA supplementation on cardiometabolic disturbances. Databases including MEDLINE, Embase, PubMed and Cochrane Trials were searched until December 2019. The pooled effects (weighted mean difference, WMD) of outcomes with moderate and high heterogeneity were calculated with a random-effects model, while low heterogeneity was calculated with a fixed-effect model. Fourteen RCTs with 1137 participants who met the eligibility criteria were pooled. Compared with participants supplemented with ALA, those who received EPA/DHA supplementation experienced a greater reduction in triglycerides (TG) (WMD -0.191 mmol l-1; 95% CI -0.249, -0.133) but a greater increase in high-density lipoprotein (HDL) (WMD 0.033 mmol l-1; 95% CI 0.004, 0.062), low-density lipoprotein (LDL) (WMD 0.130 mmol l-1; 95% CI 0.006, 0.253) and total cholesterol (TC) (WMD 0.179 mmol l-1; 95% CI 0.006, 0.352). In subgroup analyses, the WMD for TG was much lower in trials with participants >40 years old (-0.246 mmol l-1; 95% CI -0.325, -0.167). When DHA and EPA were separately administered, modest increases in HDL were observed in trials that used DHA as a supplement (0.161 mmol l-1; 95% CI 0.017, 0.304), but not in trials using EPA (0.040 mmol l-1; 95% CI -0.132, 0.212). In conclusion, dietary EPA/DHA supplementation improved the TG and HDL status but increased LDL levels in comparison with ALA.

Modulation of endothelial cell responses and vascular function by dietary fatty acids

Healthy and functional endothelial cells play important roles in maintaining vascular homeostasis, whereas endothelial dysfunction initiates and exacerbates vascular disease progression. Interventional studies with dietary fatty acids have shown that these molecules have varying effects on vascular function. It is hypothesized that the actions of dietary fatty acids on vascular function may be mediated in part through endothelial cells. This review summarizes the results of studies that have examined the acute and chronic effects of dietary fatty acids on endothelial function and vascular properties in humans, as well as the potential mechanisms by which n-3 polyunsaturated fatty acids regulate endothelial function. Altogether, this article provides an extensive review of how fatty acids contribute to vascular function through their ability to modulate endothelial cells and discusses relationships between dietary fatty acids and endothelial cells in the context of vascular dysfunction.

Dietary Fat and Blood Pressure

PURPOSE OF REVIEW

Do dietary fats lower blood pressure? This review covers total fats, individual fatty acids and foods that provide specific fats.

RECENT FINDINGS

Evidence for blood pressure lowering is stronger for supplements providing individual marine fatty acids than for fish intake since data on fish consumption are scarce. Such effects are more readily apparent in hypertensive than normal subjects. Biological mechanisms to support linkage between dietary fish oils and blood pressure are plausible. Information on other dietary fatty acids (saturates, linoleic acid, alpha-linolenic acid) is mostly less robust and therefore inconclusive. However, findings with respect to consumption of dairy foods especially of the low-fat variety do suggest association with lower blood pressures. Apart from marine fatty acids which have mostly been significantly associated with clinically modest blood pressure-lowering, the effects of other dietary fatty acids are inconsistent or clinically minor. Consumption of dairy especially of yoghurt has been linked with lower blood pressure despite the relatively high saturated fat content but the mechanism is unclear.

Use of Combined Methodologies in Assessing Food Beliefs and Habits of Elderly Greeks in Greece

This study is part of a wider cross-cultural study of food habits and health in later life. Two general approaches have been incorporated into the survey instrument: (1) rapid assessment procedures (open-ended questions) to elicit information on food and health beliefs, and (2) a questionnaire approach (coded answers for scoring) to elicit information on health, lifestyle, and usual food intake. By combining the qualitative anthropological approach on food beliefs with the conventional survey method for gathering food-intake data, it was possible to examine underlying reasons for observed food habits and consumption of various foodstuffs in 104 Greeks 70 years old or over in a town near Athens in 1988. More than 75% of the subjects believed that meat should not be eaten more than once a week because it is bad for health, that fish should be eaten twice a week because it is good for the heart, and that legumes are essential for longevity and should be eaten at least twice a week. They believed that fruit should be eaten in moderation and is not essential to health - that oranges raise blood pressure and should be avoided by the elderly, but that grapes, when eaten exclusively in large quantities, can cure all illnesses. When these beliefs were compared to actual intake, consumption in most cases, except that of legumes, was compatible with the beliefs. If the C;reek elderly community were to be targeted for health promotion, their beliefs would need to be taken into consideration to facilitate programme implementation.

Effect ofα-linolenic acid on 24-h ambulatory blood pressure in untreated high-normal and stage I hypertensive subjects

Results of intervention studies on the effects ofα-linolenic acid (ALA; C18 : 3n-3) on blood pressure (BP) are conflicting. Discrepancies between studies may be due to differences in study population, as subjects with increased baseline BP levels may be more responsive. Therefore, we examined specifically the effects of ALA on 24-h ambulatory blood pressure (ABP) in (pre-)hypertensive subjects. In a double-blind, randomised, placebo-controlled parallel study, fifty-nine overweight and obese adults (forty males and nineteen females) with (pre-)hypertension (mean age of 60 (sd8) years) received daily 10 g refined cold-pressed flaxseed oil, providing 4·7 g (approximately 2 % of energy) ALA (n29) or 10 g of high-oleic sunflower oil as control (n30) for 12 weeks. Compliance was excellent as indicated by vial count and plasma phospholipid fatty-acid composition. Compared with control, the changes of –1·4 mmHg in mean arterial pressure (MAP; 24 h ABP) after flaxseed oil intake (95 % CI –4·8, 2·0 mmHg,P=0·40) of –1·5 mmHg in systolic BP (95 % CI –6·0, 3·0 mmHg,P=0·51) and of –1·4 mmHg in diastolic BP (95 % CI –4·2, 1·4 mmHg,P=0·31) were not statistically significant. Also, no effects were found for office BP and for MAP, systolic BP, and diastolic BP when daytime and night-time BP were analysed separately and for night-time dipping. In conclusion, high intake of ALA, about 3–5 times recommended daily intakes, for 12 weeks does not significantly affect BP in subjects with (pre-)hypertension.

Effects of Flaxseed Oil on Serum Lipids and Atherosclerosis in Hypercholesterolemic Rabbits

Objective: Flaxseed oil has very high content of ox-linolenic acid (C18:3n-3, omega-3 [n-3] fatty acid). Based on the usefulness of n-3 fatty acid in fish oil against cardiovascular diseases, flaxseed oil is marketed as a health food. The n-3 fatty acid in flaxseed oil is different than that of fish oil. Indirect evidence suggests that the omega-3 fatty acid in flaxseed oil is not effective in lowering serum lipids and hypercholesterolemic atherosclerosis. The effects of flaxseed oil on serum lipids and hypercholesterolemic atherosclerosis are not known. An investigation, therefore, was made of flaxseed oil on high-cholesterol diet-induced atherosclerosis, serum lipids (triglycerides, total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, risk ratio of total cholesterol to high-density lipoprotein cholesterol), serum and aortic malondialdehyde, an index of levels of reactive oxygen species, aortic chemiluminescence (a measure of antioxidant reserve), and reactive oxygen species-producing activity of white blood cell chemiluminescence in rabbits.

Methods: The rabbits were assigned to four groups: Group I, regular diet (control); Group II, 5% flaxseed oil in regular diet; Group III, 0.5% cholesterol diet; Group IV, diet containing 0.5% cholesterol and 5% flaxseed oil. Blood samples were collected before and after 4 and 8 weeks of experimental diets for measurement of serum lipids, serum malondialdehyde, and white blood cell chemiluminescence. At the end of 8 weeks of the experimental diet, aortas were removed for measurement of atherosclerotic plaques, aortic malondialdehyde, and antioxidant reserve.

Results: Serum total cholesterol, triglycerides, and low-density and high-density lipoprotein cholesterol, and risk ratio of total cholesterol to high-density lipoprotein cholesterol, were elevated to a similar extent in Groups III and IV compared to Groups I and II. The extent of atherosclerosis in Groups III and IV was similar (56.74% ± 11.14% vs 58.01% ± 10.95%). Groups III and IV both had similar increases in serum and aortic malondialdehyde and antioxidant reserve. Reactive oxygen species-producing activity of white blood cells increased in Group III, and flaxseed oil prevented the cholesterol-induced increase in white blood cell chemiluminescence in Group IV.

Conclusion: These results suggest that flaxseed oil does not produce an alteration in serum lipids or in the extent of hypercholesterolemic atherosclerosis; however, it decreases white blood cell chemiluminescence. The ineffectiveness of flaxseed oil was associated with its ineffectiveness in altering the levels of oxidative stress.

Dietary supplementation with docosahexanoic acid (DHA) increases red blood cell membrane flexibility in mice with sickle cell disease

Humans and mice with sickle cell disease (SCD) have rigid red blood cells (RBCs). Omega-3 fatty acids, such as docosahexanoic acid (DHA), may influence RBC deformability via incorporation into the RBC membrane. In this study, sickle cell (SS) mice were fed natural ingredient rodent diets supplemented with 3% DHA (DHA diet) or a control diet matched in total fat (CTRL diet). After 8weeks of feeding, we examined the RBCs for: 1) stiffness, as measured by atomic force microscopy; 2) deformability, as measured by ektacytometry; and 3) percent irreversibly sickled RBCs on peripheral blood smears. Using atomic force microscopy, it is found that stiffness is increased and deformability decreased in RBCs from SS mice fed CTRL diet compared to wild-type mice. In contrast, RBCs from SS mice fed DHA diet had markedly decreased stiffness and increased deformability compared to RBCs from SS mice fed CTRL diet. Furthermore, examination of peripheral blood smears revealed less irreversibly sickled RBCs in SS mice fed DHA diet as compared to CTRL diet. In summary, our findings indicate that DHA supplementation improves RBC flexibility and reduces irreversibly sickled cells by 40% in SS mice. These results point to potential therapeutic benefits of dietary omega-3 fatty acids in SCD.

Plant compared with marine n-3 fatty acid effects on cardiovascular risk factors and outcomes: what is the verdict?

Plants provide α-linolenic acid [ALA; 18:3n-3 (18:3ω-3)], which can be converted via eicosapentaenoic acid (EPA; 20:5n-3) to docosahexaenoic acid (DHA; 22:6n-3), which is required for normal visual and cognitive function. Dietary ALA is provided mainly by vegetable oils, especially soybean and rapeseed oils, but is destroyed by partial hydrogenation; it is also present in high amounts in walnuts and flaxseed. Dietary EPA and DHA are provided mainly by fish and so are absent from vegan diets and only present in trace amounts in vegetarian diets. Vegetarians and vegans have lower proportions of DHA in blood and tissue lipids compared with omnivores. High intakes of EPA and DHA (typically in the range of 3-5 g/d) but not ALA have favorable effects on several cardiovascular disease (CVD) risk factors and have been postulated to delay arterial aging and cardiovascular mortality, but these intakes are beyond the range of normal dietary intake. Arterial stiffness, which is a measure of arterial aging, appears to be lower in vegans than in omnivores; and risk of CVD in vegetarians and vegans is approximately one-third that in omnivores. Prospective cohort studies showed higher intakes of EPA+DHA, and less consistently ALA, to be associated with a lower risk of CVD, especially fatal coronary heart disease, but meta-analyses of randomized controlled trials of supplementation of EPA+DHA or ALA in secondary prevention of CVD showed no clear benefit. Current evidence is insufficient to warrant advising vegans and vegetarians to supplement their diets with EPA or DHA for CVD prevention.

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.

Fish oil supplementation alters circulating eicosanoid concentrations in young healthy men

OBJECTIVE

Increasing omega-3 fatty acid (FA) intake, particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), is associated with numerous health benefits; however, the benefits on inflammation appear to vary depending on the study population examined. While improvements in inflammatory status have been reported in the elderly, there is less evidence regarding the effects of fish oil supplementation on inflammation in young adults. The goal of the present study was to examine the influence of fish oil supplementation on lipid metabolites and the inflammatory status of young healthy men.

MATERIALS/METHODS

Fasted serum samples were collected from 10 young healthy males (23.4 ± 1.7 years) before and after a 3-month supplementation of fish-oil containing 2.0g EPA and 1.0g DHA. Samples were analyzed to investigate changes in FA profiles, bioclinical parameters (e.g. triglyceride and hs-CRP), and a panel of 26 eicosanoids. Paired t-tests were used to evaluate changes between the time points.

RESULTS

Serum triglycerides decreased (P=0.0006) while the proportion of HDL-c (relative to total cholesterol) increased significantly (P=0.0495) after fish oil supplementation. Specific monounsaturated and polyunsaturated FA levels were changed following supplementation, including reductions in palmitoleic and oleic acid, and, as expected, increases in EPA and DHA. We also observed increases in eicosanoids, namely prostaglandin-F2α (P<0.0001) and thromboxane-B2 (P=0.0296), after fish oil supplementation.

CONCLUSIONS

A 3-month fish oil supplementation in young healthy men improved circulating triglyceride levels and the HDL-c ratio while, concomitantly, increasing the concentrations of two eicosanoids (prostaglandin-F2α and thromboxane-B2). This suggests that fish oil supplementation does have significant benefits in young healthy adults and that specific omega-6-derived eicosanoids can help to further our understanding regarding the beneficial link between omega-3 FA and inflammation.

Oxidation of marine omega-3 supplements and human health

Marine omega-3 rich oils are used by more than a third of American adults for a wide range of purported benefits including prevention of cardiovascular disease. These oils are highly prone to oxidation to lipid peroxides and other secondary oxidation products. Oxidized oils may have altered biological activity making them ineffective or harmful, though there is also evidence that some beneficial effects of marine oils could be mediated through lipid peroxides. To date, human clinical trials have not reported the oxidative status of the trial oil. This makes it impossible to understand the importance of oxidation to efficacy or harm. However, animal studies show that oxidized lipid products can cause harm. Oxidation of trial oils may be responsible for the conflicting omega-3 trial literature, including the prevention of cardiovascular disease. The oxidative state of an oil can be simply determined by the peroxide value and anisidine value assays. We recommend that all clinical trials investigating omega-3 harms or benefits report the results of these assays; this will enable better understanding of the benefits and harms of omega-3 and the clinical importance of oxidized supplements.

Do FADS genotypes enhance our knowledge about fatty acid related phenotypes?

Several physiological processes, such as visual and cognitive development in early life, are dependent on the availability of long-chain polyunsaturated fatty acids (LC-PUFAs). Furthermore, the concentration of LC-PUFAs in phospholipids has been associated with numerous complex diseases like cardiovascular disease, atopic disease and metabolic syndrome. The level and composition of LC-PUFAs in the human body is mainly dependent on their dietary intake or on the intake of fatty acid precursors, which are endogenously elongated and desaturated to physiologically active LC-PUFAs. The delta-5 and delta-6 desaturase are the most important enzymes in this reaction cascade. In the last few years, several studies have reported an association between single nucleotide polymorphisms (SNPs) in the two desaturase encoding genes (FADS1 and FADS2) and the concentration of omega-6 and omega-3 fatty acids. This shows that beside nutrition, genetic factors play an important role in the regulation of LC-PUFAs as well. This review focuses on current knowledge of the impact of FADS genotypes on LC-PUFA and lipid metabolism and discusses their influence on infant intellectual development, neurological conditions, metabolic disease as well as cardiovascular disease.

Meta-analysis of the effects of flaxseed interventions on blood lipids

BACKGROUND

Several clinical trials have investigated the effects of flaxseed and flaxseed-derived products (flaxseed oil or lignans) on blood lipids; however, the findings have been inconsistent.

OBJECTIVE

We aimed to identify and quantify the effectiveness of flaxseed and its derivatives on blood lipid profiles.

DESIGN

A comprehensive literature search was performed on the basis of English reports of randomized controlled trials of flaxseed or its derivatives on lipid profiles in adults, which were published from January 1990 to October 2008. Attempts also were made to access unpublished data. Study quality was assessed by using the Jadad score, and a meta-analysis was conducted.

RESULTS

Twenty-eight studies were included. Flaxseed interventions reduced total and LDL cholesterol by 0.10 mmol/L (95% CI: -0.20, 0.00 mmol/L) and 0.08 mmol/L (95% CI: -0.16, 0.00 mmol/L), respectively; significant reductions were observed with whole flaxseed (-0.21 and -0.16 mmol/L, respectively) and lignan (-0.28 and -0.16 mmol/L, respectively) supplements but not with flaxseed oil. The cholesterol-lowering effects were more apparent in females (particularly postmenopausal women), individuals with high initial cholesterol concentrations, and studies with higher Jadad scores. No significant changes were found in the concentrations of HDL cholesterol and triglycerides.

CONCLUSIONS

Flaxseed significantly reduced circulating total and LDL-cholesterol concentrations, but the changes were dependent on the type of intervention, sex, and initial lipid profiles of the subjects. Further studies are needed to determine the efficiency of flaxseed on lipid profiles in men and premenopausal women and to explore its potential benefits on other cardiometabolic risk factors and prevention of cardiovascular disease.

Does genetic variation in the Delta6-desaturase promoter modify the association between alpha-linolenic acid and the prevalence of metabolic syndrome?

BACKGROUND

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are associated with protection against components of the metabolic syndrome, but the role of alpha-linolenic acid (ALA), the metabolic precursor of EPA and DHA, has not been studied. The Delta(6)-desaturase enzyme converts ALA into EPA and DHA, and genetic variation in the Delta(6)-desaturase gene (FADS2) may affect this conversion.

OBJECTIVES

We hypothesize that high ALA is associated with a lower prevalence of the metabolic syndrome and that genetic variation in FADS2 modifies this association.

DESIGN

We studied 1815 Costa Rican adults. Adipose tissue ALA was used as a biomarker of intake, and metabolic syndrome was identified with the definition from the National Cholesterol Education Program, Adult Treatment Panel III. Prevalence ratios (PRs) and 95% CIs were estimated from binomial regression models, and the likelihood ratio was used to test for effect modification.

RESULTS

High concentrations of adipose tissue ALA were associated with lower PRs of the metabolic syndrome compared with low ALA (0.81; 95% CI: 0.66, 1.00, for the comparison between the highest and the lowest quintiles; P for trend < 0.02). Higher concentrations of adipose tissue ALA were associated with a lower PR among homozygote (0.67; 95% CI: 0.53, 0.86) and heterozygote (0.84; 95% CI: 0.72, 0.99) carriers of the FADS2 T allele, but not among homozygote carriers of the deletion variant allele (0.99; 95% CI: 0.78, 1.27; P for interaction: 0.08).

CONCLUSIONS

Elevated ALA concentrations in adipose tissue are associated with lower prevalence of the metabolic syndrome. A lack of association among homozygote carriers of the FADS2 deletion allele suggests that this association may be due in part to the conversion of ALA into EPA.

Benefits of fish oil supplementation in hyperlipidemia: a systematic review and meta-analysis

BACKGROUND

Fish oils have been widely reported as a useful supplement to reduce fasting blood triglyceride levels in individuals with hyperlipidemia. We performed an updated meta-analysis to quantitatively evaluate all the randomized trials of fish oils in hyperlipidemic subjects.

METHODS

We conducted a systematic literature search using several electronic databases supplemented by manual searches of published reference lists, review articles and conference abstracts. We included all placebo-controlled randomized trials of parallel design that evaluated any of the main blood lipid outcomes: total, high-density lipoprotein (HDL) and low-density lipoprotein (LDL) cholesterol or triglycerides (TG). Data were pooled using DerSimonian-Laird's random effects model.

RESULTS

The final analysis comprised of 47 studies in otherwise untreated subjects showed that taking fish oils (weighted average daily intake of 3.25 g of EPA and/or DHA) produced a clinically significant reduction of TG (-0.34 mmol/L, 95% CI: -0.41 to -0.27), no change in total cholesterol (-0.01 mmol/L, 95% CI: -0.03 to 0.01) and very slight increases in HDL (0.01 mmol/L, 95% CI: 0.00 to 0.02) and LDL cholesterol (0.06 mmol/L, 95% CI: 0.03 to 0.09). The reduction of TG correlated with both EPA+DHA intake and initial TG level.

CONCLUSION

Fish oil supplementation produces a clinically significant dose-dependent reduction of fasting blood TG but not total, HDL or LDL cholesterol in hyperlipidemic subjects.

Dietary α-linolenic acid and health-related outcomes: a metabolic perspective

α-Linolenic acid (αLNA; 18: 3n-3) is essential in the human diet, probably because it is the substrate for the synthesis of longer-chain, more unsaturatedn-3 fatty acids, principally EPA (20: 5n-3) and DHA (22: 6n-3), which confer important biophysical properties on cell membranes and so are required for tissue function. The extent to which this molecular transformation occurs in man is controversial. The present paper reviews the recent literature on the metabolism of αLNA in man, including the use of dietary αLNA in β-oxidation, recycling of carbon by fatty acid synthesisde novoand conversion to longer-chain PUFA. Sex differences in αLNA metabolism and the possible biological consequences are discussed. Increased consumption of EPA and DHA in fish oil has a number of well-characterised beneficial effects on health. The present paper also reviews the efficacy of increased αLNA consumption in increasing the concentrations of EPA and DHA in blood and cell lipid pools, and the extent to which such dietary interventions might be protective against CVD and inflammation. Although the effects on CVD risk factors and inflammatory markers are variable, where beneficial effects have been reported these are weaker than have been achieved from increasing consumption of EPA+DHA or linoleic acid. Overall, the limited capacity for conversion to longer-chainn-3 fatty acids, and the lack of efficacy in ameliorating CVD risk factors and inflammatory markers in man suggests that increased consumption of αLNA may be of little benefit in altering EPA+DHA status or in improving health outcomes compared with other dietary interventions.

Bio F1B hamster: a unique animal model with reduced lipoprotein lipase activity to investigate nutrient mediated regulation of lipoprotein metabolism

Background

Bio F₁B hamster is an inbred hybrid strain that is highly susceptible to diet-induced atherosclerosis. We previously reported that feeding a high fat fish oil diet to Bio F₁B hamster caused severe hyperlipidaemia. In this study we compared the effects of various diets in the Bio F₁B hamster and the Golden Syrian hamster, which is an outbred hamster strain to investigate whether genetic background plays an important role in dietary fat mediated regulation of lipoprotein metabolism. We further investigated the mechanisms behind diet-induced hyperlipidaemia in F₁B hamster.

Methods

The Bio F₁B and Golden Syrian hamsters, 8 weeks old, were fed high fat diets rich in either monounsaturated fatty acids, an n-6: n-3 ratio of 5 or a fish oil diet for 4 weeks. Animals were fasted overnight and blood and tissue samples were collected. Plasma was fractionated into various lipoprotein fractions and assayed for triacylglycerol and cholesterol concentrations. Plasma lipoprotein lipase activity was measured using radioisotope method. Microsomal triglyceride transfer protein activity was measured in the liver and intestine. Plasma apolipoproteinB48, -B100 and apolipoprotein E was measured using Western blots. Two-way ANOVA was used to determine the effect of diet type and animal strain.

Results

The fish oil fed F₁B hamsters showed milky plasma after a 14-hour fast. Fish oil feeding caused accumulation of apolipoproteinB48 containing lipoprotein particles suggesting hindrance of triglyceride-rich lipoprotein clearance. There was no significant effect of diet or strain on hepatic or intestinal microsomal triglyceride transfer protein activity indicating that hyperlipidaemia is not due to an increase in the assembly or secretion of lipoprotein particles. F₁B hamsters showed significantly reduced levels of lipoprotein lipase activity, which was inhibited by fish oil feeding.

Conclusion

Evidence is presented for the first time that alterations in lipoprotein lipase activity and mRNA levels contribute to varied response of these hamsters to dietary fat, highlighting the importance of genetic background in the regulation of lipid and lipoprotein metabolism by dietary fats. Bio F₁B hamster may prove to be an important animal model to investigate nutrient mediated regulation of metabolic parameters under lipoprotein lipase deficiency.

A review of omega-3 ethyl esters for cardiovascular prevention and treatment of increased blood triglyceride levels

The two marine omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), prevalent in fish and fish oils, have been investigated as a strategy towards prophylaxis of atherosclerosis. While the results with fish and fish oils have been not as clear cut, the data generated with the purified ethyl ester forms of these two fatty acids are consistent. Although slight differences in biological activity exist between EPA and DHA, both exert a number of positive actions against atherosclerosis and its complications. EPA and DHA as ethyl esters inhibit platelet aggregability, and reduce serum triglycerides, while leaving other serum lipids essentially unaltered. Glucose metabolism has been studied extensively, and no adverse effects were seen. Pro-atherogenic cytokines are reduced, as are markers of endothelial activation. Endothelial function is improved, vascular occlusion is reduced, and the course of coronary atherosclerosis is mitigated. Heart rate is reduced, and heart rate variability is increased by EPA and DHA. An antiarrhythmic effect can be demonstrated on the supraventricular and the ventricular level. More importantly, two large studies showed reductions in clinical endpoints like sudden cardiac death or major adverse cardiac events. As a consequence, relevant cardiac societies recommend using 1 g/day of EPA and DHA for cardiovascular prevention, after a myocardial infarction and for prevention of sudden cardiac death.

Replacement of linoleic acid with α-linolenic acid does not alter blood lipids in normolipidaemic men

The effect of partial dietary replacement of linoleic acid (18:2n-6; linoleic acid-rich diet) with α-linolenic acid (18:3n-3; α-linolenic acid-rich diet) on plasma lipids was investigated in twenty-nine healthy young men. After a 2-week stabilization period subjects were randomly assigned to either the α-linolenic acid-rich diet group (n15), receiving a mean of 10.1 g of α-linolenic acid and 12.1 g of linoleic acid/d, or the linoleic acid-rich diet group (n14), receiving a mean of 1.0 g of α-linolenic acid and 21.0 g of linoleic acid/d, for a 6-week test period. Blood samples were taken at the commencement of the stabilization period and at the start (week 0), midpoint (week 3) and endpoint (week 6) of the test period and plasma lipids analysed. The changes occurring on the linoleic acid-rich diet and α-linolenic acid-rich diet were compared but no significant differences in the changes in plasma total cholesterol, LDL-cholesterol, HDL-cholesterol, the subfractions HDL2and HDL3or triacylglycerols were found. These results indicate that dietary replacement of linoleic acid with α-linolenic acid in the diet of healthy male subjects offers similar cardioprotective benefits with respect to lipid metabolism.

Dietary supplementation with flaxseed oil lowers blood pressure in dyslipidaemic patients

OBJECTIVE

Alpha-linolenic acid (ALA) is the natural precursor of the cardioprotective long-chain n-3 fatty acids. Available data indicate a possible beneficial effect of ALA on cardiovascular disease (CVD), but the response of various CVD risk factors to increased ALA intake is not well characterized. The purpose of the present study was to examine the effect of increased ALA intake on blood pressure in man. DESIGN, SETTING, SUBJECTS AND INTERVENTIONS: We used a prospective, two-group, parallel-arm design to examine the effect of a 12-week dietary supplementation with flaxseed oil, rich in ALA (8 g/day), on blood pressure in middle-aged dyslipidaemic men (n=59). The diet of the control group was supplemented with safflower oil, containing the equivalent n-6 fatty acid (11 g/day linoleic acid (LA); n=28). Arterial blood pressure was measured at the beginning and at the end of the dietary intervention period.

RESULTS

Supplementation with ALA resulted in significantly lower systolic and diastolic blood pressure levels compared with LA (P=0.016 and P=0.011, respectively, from analysis of variance (ANOVA) for repeated measures).

CONCLUSIONS

We observed a hypotensive effect of ALA, which may constitute another mechanism accounting in part for the apparent cardioprotective effect of this n-3 fatty acid.

Effects of altering the ratio of dietary n-6 to n-3 fatty acids on insulin sensitivity, lipoprotein size, and postprandial lipemia in men and postmenopausal women aged 45-70 y: the OPTILIP Study

BACKGROUND

Insulin resistance is associated with elevated plasma triacylglycerol, low HDL concentrations, elevated postprandial lipemia, and a predominance of small, dense LDLs (sdLDLs). It has been hypothesized that the dietary ratio of n-6 to n-3 (n-6:n-3) polyunsaturated fatty acids (PUFAs) may have favorable effects on these risk factors by increasing insulin sensitivity.

OBJECTIVE

The objective was to measure changes in insulin sensitivity, lipoprotein size, and postprandial lipemia after a 6-mo alteration in n-6:n-3.

DESIGN

In a randomized, parallel design in 258 subjects aged 45-70 y, we compared 4 diets providing 6% of energy as PUFAs with an n-6:n-3 between 5:1 and 3:1 with a control diet that had an n-6:n-3 of 10:1. The diets were enriched in alpha-linolenic acid, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), or both. Insulin sensitivity was assessed with the homeostatic model assessment of insulin resistance and the revised quantitative insulin sensitivity test.

RESULTS

Dietary intervention did not influence insulin sensitivity or postprandial lipase activities. Fasting and postprandial triacylglycerol concentrations were lower, and the proportion of sdLDLs decreased (by 12.7%; 95% CI: -22.9%, 2.4%), with an n-6:n-3 of approximately 3:1, which was achieved by the addition of long-chain n-3 PUFAs (EPA and DHA).

CONCLUSIONS

Decreasing the n-6:n-3 does not influence insulin sensitivity or lipase activities in older subjects. The reduction in plasma triacylglycerol after an increased intake of n-3 long-chain PUFAs results in favorable changes in LDL size.

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.

Effect of alpha linolenic acid on cardiovascular risk markers: a systematic review

OBJECTIVE

To determine whether dietary supplementation with alpha linolenic acid (ALA) can modify established and emerging cardiovascular risk markers.

DESIGN

Systematic review and meta-analysis of randomised controlled trials identified by a search of Medline, Embase, Cochrane Controlled Trials Register (CENTRAL), and the metaRegister of Controlled Trials (mRCT).

PATIENTS

All human studies were reviewed.

MAIN OUTCOME MEASURES

Changes in concentrations of total cholesterol, low density lipoprotein (LDL) cholesterol, high density lipoprotein (HDL) cholesterol, very low density lipoprotein (VLDL) cholesterol, triglyceride, fibrinogen, and fasting plasma glucose, and changes in body mass index, weight, and systolic and diastolic blood pressure.

RESULTS

14 studies with minimum treatment duration of four weeks were reviewed. ALA had a significant effect on three of the 32 outcomes examined in these studies. Concentrations of fibrinogen (0.17 micromol/l, 95% confidence interval (CI) -0.30 to -0.04, p = 0.01) and fasting plasma glucose (0.20 mmol/l, 95% CI -0.30 to -0.10, p < 0.01) were reduced. There was a small but clinically unimportant decrease in HDL (0.01 mmol/l, 95% CI -0.02 to 0.00, p < 0.01). Treatment with ALA did not significantly modify total cholesterol, triglycerides, weight, body mass index, LDL, diastolic blood pressure, systolic blood pressure, VLDL, and apolipoprotein B.

CONCLUSIONS

Although ALA supplementation may cause small decreases in fibrinogen concentrations and fasting plasma glucose, most cardiovascular risk markers do not appear to be affected. Further trials are needed, but dietary supplementation with ALA to reduce cardiovascular disease cannot be recommended.

Apolipoprotein E genotype in dyslipidemic patients and response of blood lipids and inflammatory markers to alpha-linolenic Acid

The objective of this study was to determine the effect of alpha-linolenic acid (ALA) supplementation on blood lipids and inflammatory markers, in relation to apolipoprotein (apo) E genotype. The diets of 50 dyslipidemic male patients were supplemented with 15 mL of flaxseed oil per day for 12 weeks. Retrospectively, 3 apo E genotype variants were found (epsilon2/epsilon3, n=7; epsilon3/epsilon3, n=33; epsilon3/epsilon4, n=10). No significant differences were found among apo E genotypes in any variables at baseline. ALA supplementation produced a small but significant decrease in high-density lipoprotein cholesterol (from 1.12 to 1.08 mmol/L, 43 to 42 mg/dL; p=0.008) and apo A-I levels (from 1.28 to 1.24 g/L, p=0.036) in the epsilon3/epsilon3 homozygotes. In addition, ALA supplementation resulted in a significant decrease in the serum concentration of serum amyloid A (SAA) (p=0.014), C-reactive protein (CRP) (p=0.013), macrophage colony-stimulating factor (MCSF) (p<0.001), and interleukin (IL)-6 (p=0.028). Serum SAA and MCSF were also significantly decreased in the epsilon3/epsilon4 group (p=0.005 and p=0.017, respectively). In contrast, ALA produced no effects on any of the inflammatory markers in the epsilon2/epsilon3 group. ALA may have beneficial effects on inflammation in dyslipidemic carriers of the apo epsilon3/epsilon3 and epsilon3/epsilon4 genotypes, but not in carriers of the epsilon2 allele.

Dietary Linolenic Acid Is Associated With a Lower Prevalence of Hypertension in the NHLBI Family Heart Study

Dietary linolenic acid has been shown to be associated with coronary artery disease. However, limited data are available on its effects on blood pressure. We used data from 4594 white participants (aged 25 to 93 years) in the National Heart, Lung, and Blood Institute (NHLBI) Family Heart Study to evaluate whether dietary linolenic acid was associated with prevalent hypertension and resting blood pressure. We used generalized estimating equations to determine the prevalence odds ratios (ORs) of hypertension and adjusted means of systolic and diastolic blood pressure across quartiles of linolenic acid. Mean dietary linolenic acid intake was 0.81±0.35 g per day for men and 0.69±0.29 g per day for women. From the lowest to the highest quartile of linolenic acid, multivariable adjusted ORs (95% confidence interval [CI]) for hypertension were 1.0 (reference), 0.73 (0.56 to 0.95), 0.71 (0.53 to 0.95), and 0.67 (0.47 to 0.96), respectively ( P for trend 0.04), controlling for age, sex, energy intake, body mass index, risk group, study site, education, smoking, alcohol intake, exercise, and history of coronary artery disease and diabetes mellitus. Dietary linolenic acid was related inversely to resting systolic ( P for trend 0.03) but not diastolic blood pressure ( P for trend 0.43). Linoleic acid, an omega-6 fatty acid, was not associated with prevalent hypertension or blood pressure. These data suggest that dietary linolenic acid is associated with a lower prevalence of hypertension and lower systolic blood pressure in white subjects.

Dietary n-6 and n-3 fatty acid balance and cardiovascular health

Epidemiological and clinical studies have established that the n-6 fatty acid, linoleic acid (LA), and the n-3 fatty acids, linolenic acid (LNA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) collectively protect against coronary heart disease (CHD). LA is the major dietary fatty acid regulating low-density lipoprotein (LDL)-C metabolism by downregulating LDL-C production and enhancing its clearance. Further, the available mass of LA is a critical factor determining the hyperlipemic effects of other dietary fat components, such as saturated and trans fatty acids, as well as cholesterol. By contrast, n-3 fatty acids, especially EPA and DHA, are potent antiarryhthmic agents. EPA and DHA also improve vascular endothelial function and help lower blood pressure, platelet sensitivity, and the serum triglyceride level. The distinct functions of these two families make the balance between dietary n-6 and n-3 fatty acids an important consideration influencing cardiovascular health. Based on published literature describing practical dietary intakes, we suggest that consumption of ~6% en LA, 0.75% en LNA, and 0.25% en EPA + DHA represents adequate and achievable intakes for most healthy adults. This corresponds to an n-6/n-3 ratio of ~6:1. However, the absolute mass of essential fatty acids consumed, rather than their n-6/n-3 ratio, should be the first consideration when contemplating lifelong dietary habits affecting cardiovascular benefit from their intake.

Effects of dietary alpha linolenic acid on cholesterol metabolism in male and female hamsters of the LPN strain

N-3 polyunsaturated fatty acids and estrogens are recognized as protective factors of atherosclerosis, however their interactions on cholesterol metabolism remain unclear. Male and female hamsters were fed for 9 weeks diets containing 12.5% lipids and rich in either alpha-linolenic acid ("linseed" diet) or saturated fatty acids ("butter" diet). Hamsters fed the "linseed" diet exhibited lower plasma concentrations of cholesterol (-29%), total LDL (-35%) and HDL (-17%), glucose (-20%), insulin (-40%) and of the LDL-cholesterol/HDL-cholesterol ratio (-27%) than those fed the "butter" diet. In the liver, cholesterol content was 2.7-fold lower in response to the "linseed" diet, whereas the concentration of HDL receptor (SR-BI) and the activities of HMGCoA reductase and cholesterol 7alpha-hydroxylase were 30 to 50% higher than with the "butter" diet. By contrast, the LDL receptor concentration did not vary with the diet. Females exhibited higher concentration of LDL (+24%), lower concentration of plasma triglycerides (-34%), total VLDL (-46%) and VLDL-cholesterol (-37%) and of biliary phospholipids (-19%). Besides, there was also an interaction between gender and diet: in males fed the "butter" diet, plasma triglycerides and VLDL concentration, were 2 to 4 fold higher than in the other groups. These data suggest that gene and/or metabolic regulations by fatty acids could interact with that of sex hormones and explain why males are more sensitive to dietary fatty acids.

Flaxseed and cardiovascular risk

Flaxseed has recently gained attention in the area of cardiovascular disease primarily because it is the richest known source of both alpha-linolenic acid (ALA) and the phytoestrogen, lignans, as well as being a good source of soluble fiber. Human studies have shown that flaxseed can modestly reduce serum total and low-density lipoprotein cholesterol concentrations, reduce postprandial glucose absorption, decrease some markers of inflammation, and raise serum levels of the omega-3 fatty acids, ALA and eicosapentaenoic acid. Data on the antiplatelet, antioxidant, and hypotensive effects of flaxseed, however, are inconclusive. More research is needed to define the role of this functional food in reducing cardiovascular risk.

Alpha-linolenic acid metabolism in men and women: nutritional and biological implications

PURPOSE OF REVIEW

This review critically evaluates current knowledge of alpha-linolenic acid metabolism in adult humans based on the findings of studies using stable isotope tracers and on increased dietary alpha-linolenic acid intake. The relative roles of alpha-linolenic acid and of longer-chain polyunsaturated fatty acids in cell structure and function are discussed together with an overview of the major metabolic fates of alpha-linolenic acid. The extent of partitioning towards beta-oxidation and carbon recycling in humans is described. The use and limitations of stable isotope tracers to estimate alpha-linolenic acid desaturation and elongation are discussed. A consensus view of the extent of alpha-linolenic acid conversion to longer-chain fatty acids in humans is presented. The extent to which increasing dietary alpha-linolenic acid intake alters the concentrations of longer-chain n-3 fatty acids is described. The biological and nutritional implications of these findings are discussed.

RECENT FINDINGS

Conversion of alpha-linolenic acid to eicosapentaenoic acid is limited in men and further transformation to docosahexaenoic acid is very low. A lower proportion of alpha-linolenic acid is used as a substrate for beta-oxidation in women compared with men, while the fractional conversion to longer-chain fatty acids is greater, possibly due to the regulatory effects of oestrogen.

SUMMARY

Overall, alpha-linolenic acid appears to be a limited source of longer-chain n-3 fatty acids in man and so adequate intakes of preformed n-3 polyunsaturated fatty acids, in particular docosahexaenoic acid, may be important for maintaining optimal tissue function. Capacity to upregulate alpha-linolenic acid transformation in women may be important for meeting the demands of the fetus and neonate for docosahexaenoic acid.