The association and dose–response relationship between dietary intake of α -linolenic acid and risk of CHD: a systematic review and meta-analysis of cohort studies

Evaluating the health impact of increased linseed consumption in the Danish population

Consumption of linseeds has been suggested to have beneficial effects on human health. However, toxic constituents of linseed may compromise these benefits. We conducted a quantitative risk-benefit assessment to evaluate the overall health impact of increasing linseed intake up to 45 g/day in the Danish population (15-74 years). We quantified the risks associated with increased cadmium exposure and the benefits associated with increased intake of dietary fibre. Increased intakes of alpha-linoleic acid (ALA) were included in a sensitivity analysis. The overall health impact of different linseed intake scenarios was estimated in terms of Disability-Adjusted Life Years (DALYs). We found that the beneficial effects of linseed due to increased intake of dietary fibre outweighed the adverse health effects due to increased cadmium exposure in all scenarios. Up to 670 DALYs/100,000 individuals could be averted per year by increasing linseed consumption in the Danish population. The estimated beneficial health impact increased further when including ALA in the assessment. Different sources of uncertainty might affect the results, and more research is needed on both the health effects associated with intake of linseed and its constituents, and the bioavailability of ALA and cadmium from linseed to further improve the risk-benefit assessment.

Meta-analysis of the efficacy of ω-3 polyunsaturated fatty acids when treating patients with polycystic ovary syndrome

OBJECTIVE

To systematically assess the efficacy of ω-3 polyunsaturated fatty acids (PUFAs) when treating polycystic ovary syndrome (PCOS).

METHODS

This meta-analysis follows Preferred Reporting Items for Systematic Reviews and Meta-Analyses criteria. We searched PubMed, EMBASE, ScienceDirect, Cochrane Library, China journal full-text database, VIP full-text Database, Wanfang Database, and Chinese Biomedical Literature Data for clinical trials on ω-3 PUFAs' efficacy in treating PCOS. Two independent reviewers examined and analyzed studies, resolving inconsistencies through discussion. RevMan5.3 software performed heterogeneity-based fixed and random-effects meta-analysis. We assessed bias using the Cochrane bias risk assessment tool.

RESULTS

Our meta-analysis included 7 clinical control studies comprising 574 samples to evaluate the impact of ω-3 PUFAs on various metabolic markers in PCOS patients. We observed a significant reduction in total cholesterol (TC) and triglyceride (TG) levels (P < .05), along with a decrease in insulin resistance as measured by the Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) (P < .05). Testosterone (T) levels were also lowered in the study group post-treatment (P < .05). However, no notable effects were found on body mass index (BMI), fasting blood sugar (FBS), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and Ferriman-Gallwey (mFG) scores (P > .05). Publication bias was not detected, enhancing the robustness of our results. Our study suggests that ω-3 PUFAs could be beneficial in managing specific metabolic markers in PCOS, although the results showed marked heterogeneity.

CONCLUSION

In PCOS patients, PUFAs can enhance reproductive endocrine, glucose, and lipid levels. However, additional research and extended follow-up are required to confirm this.

Alpha-Linolenic Acid and Cardiovascular Events: A Narrative Review

Cardiovascular diseases (CVDs) represent the leading cause of global mortality with 1.7 million deaths a year. One of the alternative systems to drug therapy to minimize the risk of CVDs is represented by alpha-linolenic acid (ALA), an essential fatty acid of the omega-3 series, known for its cholesterol-lowering effect. The main purpose of this review is to analyze the effects of ALA and investigate the relevant omega-6/omega-3 ratio in order to maintain functionally beneficial effects. Concerning the lipid-lowering preventive effects, ALA may favorably affect the values of LDL-C and triglycerides in both adult and pediatric populations. Furthermore, ALA has shown protective effects against hypertension, contributing to balancing blood pressure through customary diet. According to the 2009 EFSA statement, dietary ALA may contribute to reducing the risk of CVDs, thanks to anti-hypertensive, anti-atherosclerotic and cardioprotective effects.

Beneficial Effects of Dietary Flaxseed Oil through Inflammation Pathways and Gut Microbiota in Streptozotocin-Induced Diabetic Mice

Flaxseed oil (FO) has displayed potential anti-diabetes properties by providing a high content of α-linolenic acid. However, the effects and mechanisms of FO on type 1 diabetes are still unclear. The present study aims to explore the effects of different doses of FO feeding on hepatic inflammation and gut microbiota in streptozotocin-induced diabetic mice. Forty-eight six-week-old C57BL/6J male mice were divided into a control group (CON), a diabetic group (MOD), a diabetes with 7.0% w/w FO feeding group (FO-L), and a diabetes with 10.5% w/w FO feeding group (FO-H) for six weeks. The 7.0% w/w and 10.5% w/w FO feeding groups exhibited potential recovery of the number and size of pancreas tissues. The fasting blood glucose level was significantly decreased only after 4 weeks of feeding with 10.5% w/w FO in diabetic mice. The 10.5% w/w FO feeding group significantly decreased the postprandial blood glucose level of mice in the OGTT test. Hepatic glycogen levels were dramatically upregulated in the mice fed with both 7.0% w/w and 10.5% w/w FO. FO feeding significantly attenuated hepatic LPS, TNF-α, and IL-1β levels. In addition, we observed that 7.0% w/w and 10.5% w/w FO feedings notably downregulated hepatic gene and protein expressions of TLR4, MyD88, and P65. Furthermore, only 10.5% FO regulated fecal microbiota by increasing the relative abundance of the Bacteroidetes phylum, Lactococcus family, and Muribaculaceae and Streptococcaceae family and genus in streptozotocin-induced diabetic mice. Therefore, we conclude that FO feeding plays a role in anti-inflammation via the regulation of hepatic LPS/TLR4/MyD88 pathways and gut microbiota. In addition, different doses of FO supplementation may exhibit varying mechanisms in streptozotocin-induced mice.

Oxylipin secretion by human CD3+ T lymphocytes in vitro is modified by the exogenous essential fatty acid ratio and life stage

Immune function changes across the life stages; for example, senior adults exhibit a tendency towards a weaker cell-mediated immune response and a stronger inflammatory response than younger adults. This might be partly mediated by changes in oxylipin synthesis across the life course. Oxylipins are oxidation products of polyunsaturated fatty acids (PUFAs) that modulate immune function and inflammation. A number of PUFAs are precursors to oxylipins, including the essential fatty acids (EFAs) linoleic acid (LA) and α-linolenic acid (ALA). LA and ALA are also substrates for synthesis of longer chain PUFAs. Studies with stable isotopes have shown that the relative amounts of LA and ALA can influence their partitioning by T lymphocytes between conversion to longer chain PUFAs and to oxylipins. It is not known whether the relative availability of EFA substrates influences the overall pattern of oxylipin secretion by human T cells or if this changes across the life stages. To address this, the oxylipin profile was determined in supernatants from resting and mitogen activated human CD3+ T cell cultures incubated in medium containing an EFA ratio of either 5:1 or 8:1 (LA : ALA). Furthermore, oxylipin profiles in supernatants of T cells from three life stages, namely fetal (derived from umbilical cord blood), adults and seniors, treated with the 5:1 EFA ratio were determined. The extracellular oxylipin profiles were affected more by the EFA ratio than mitogen stimulation such that n-3 PUFA-derived oxylipin concentrations were higher with the 5:1 EFA ratio than the 8:1 ratio, possibly due to PUFA precursor competition for lipoxygenases. 47 oxylipin species were measured in all cell culture supernatants. Extracellular oxylipin concentrations were generally higher for fetal T cells than for T cells from adult and senior donors, although the composition of oxylipins was similar across the life stages. The contribution of oxylipins towards an immunological phenotype might be due to the capacity of T cells to synthesize oxylipins rather than the nature of the oxylipins produced.

Fatty acids act on vascular endothelial cells and influence the development of cardiovascular disease

Endothelial cells (ECs) maintain the health of blood vessels and prevent the development of cardiovascular disease (CVD). Free saturated fatty acids (FAs) induce EC damage and increase the risk of CVD by promoting arteriosclerosis. Conversely, polyunsaturated FAs (PUFAs), such as docosahexaenoic acid, are thought to suppress EC damage induced during the early stages of CVD. This review describes the effects of multiple dietary FAs on EC disorders involved in the development of CVD. The roles of FAs in atherosclerosis and CVD were analyzed by evaluating articles published in PubMed, Science Direct, and Web of Science. Saturated FAs were found to induce EC damage by reducing the production and action of EC-derived nitric oxide. Oxidative stress, inflammation, and the renin-angiotensin system were found to be involved in EC disorder. Furthermore, n-3 PUFAs were found to reduce EC dysfunction and prevent the development of EC disorder. These results indicate that FAs may affect EC failure induced during the early stages of CVD and reduce the risk of developing the disease.

The Role of α-Linolenic Acid and Its Oxylipins in Human Cardiovascular Diseases

α-linolenic acid (ALA) is an essential C-18 n-3 polyunsaturated fatty acid (PUFA), which can be elongated to longer n-3 PUFAs, such as eicosapentaenoic acid (EPA). These long-chain n-3 PUFAs have anti-inflammatory and pro-resolution effects either directly or through their oxylipin metabolites. However, there is evidence that the conversion of ALA to the long-chain PUFAs is limited. On the other hand, there is evidence in humans that supplementation of ALA in the diet is associated with an improved lipid profile, a reduction in the inflammatory biomarker C-reactive protein (CRP) and a reduction in cardiovascular diseases (CVDs) and all-cause mortality. Studies investigating the cellular mechanism for these beneficial effects showed that ALA is metabolized to oxylipins through the Lipoxygenase (LOX), the Cyclooxygenase (COX) and the Cytochrome P450 (CYP450) pathways, leading to hydroperoxy-, epoxy-, mono- and dihydroxylated oxylipins. In several mouse and cell models, it has been shown that ALA and some of its oxylipins, including 9- and 13-hydroxy-octadecatrienoic acids (9-HOTrE and 13-HOTrE), have immunomodulating effects. Taken together, the current literature suggests a beneficial role for diets rich in ALA in human CVDs, however, it is not always clear whether the described effects are attributable to ALA, its oxylipins or other substances present in the supplemented diets.

α-Linolenic Acid Screened by Molecular Docking Attenuates Inflammation by Regulating Th1/Th2 Imbalance in Ovalbumin-Induced Mice of Allergic Rhinitis

α-Linolenic acid (ALA) is a natural essential fatty acid widely found in plant seed oils and beans, which shows positive anti-inflammatory and antiallergic effects. In our previous study, ALA was proven to bind tightly to the seven protein targets closely associated with allergic rhinitis (AR) by molecular docking, which indicates that ALA may have a potential role in the treatment of AR. A mouse model of AR induced by ovalbumin (OVA) was adopted in this study to explore the therapeutical effect and potential mechanism of ALA in treating AR. Results demonstrated that ALA remarkably relieved the nasal symptoms, reduced the OVA-sIgE level in the serum, relieved the histopathological injuries, and downregulated the mRNA expression levels of IL-6 and IL-1β in the nasal mucosa. ALA also remarkably moderated the imbalance of Th1/Th2 cells, increased the mRNA expression levels of T-bet and STAT1, and reduced GATA3 and STAT6. ALA was proven to have a substantial therapeutic effect on mice with AR, and the underlying mechanism was likely to be the regulation of Th1/Th2 imbalance through the JAK/T-bet/STAT1 and JAK/GATA3/STAT6 pathways. This study provides a specific experimental basis for the clinical use and drug development of ALA in the treatment of AR.

A New Evidence-Based Diet Score to Capture Associations of Food Consumption and Chronic Disease Risk

Previously, the attempt to compile German dietary guidelines into a diet score was predominantly not successful with regards to preventing chronic diseases in the EPIC-Potsdam study. Current guidelines were supplemented by the latest evidence from systematic reviews and expert papers published between 2010 and 2020 on the prevention potential of food groups on chronic diseases such as type 2 diabetes, cardiovascular diseases and cancer. A diet score was developed by scoring the food groups according to a recommended low, moderate or high intake. The relative validity and reliability of the diet score, assessed by a food frequency questionnaire, was investigated. The consideration of current evidence resulted in 10 key food groups being preventive of the chronic diseases of interest. They served as components in the diet score and were scored from 0 to 1 point, depending on their recommended intake, resulting in a maximum of 10 points. Both the reliability (r = 0.53) and relative validity (r = 0.43) were deemed sufficient to consider the diet score as a stable construct in future investigations. This new diet score can be a promising tool to investigate dietary intake in etiological research by concentrating on 10 key dietary determinants with evidence-based prevention potential for chronic diseases.

An Empirical Evaluation of the Impact Scenario of Pooling Bodies of Evidence from Randomized Controlled Trials and Cohort Studies in Nutrition Research

Only very few Cochrane nutrition reviews include cohort studies (CSs), but most evidence in nutrition research comes from CSs. We aimed to pool bodies of evidence (BoE) from randomized controlled trials (RCTs) derived from Cochrane reviews with matched BoE from CSs. The Cochrane Database of Systematic Reviews and MEDLINE were searched for systematic reviews (SRs) of RCTs and SRs of CSs. BoE from RCTs were pooled together with BoE from CSs using random-effects and common-effect models. Heterogeneity, 95% prediction intervals, contributed weight of BoE from RCTs to the pooled estimate, and whether integration of BoE from CSs modified the conclusion from BoE of RCTs were evaluated. Overall, 80 diet-disease outcome pairs based on 773 RCTs and 720 CSs were pooled. By pooling BoE from RCTs and CSs with a random-effects model, for 45 (56%) out of 80 diet-disease associations the 95% CI excluded no effect and showed mainly a reduced risk/inverse association. By pooling BoE from RCTs and CSs, median I2 = 46% and the median contributed weight of RCTs to the pooled estimates was 34%. The direction of effect between BoE from RCTs and pooled effect estimates was rarely opposite (n = 17; 21%). The integration of BoE from CSs modified the result (by examining the 95% CI) from BoE of RCTs in 35 (44%) of the 80 diet-disease associations. Our pooling scenario showed that the integration of BoE from CSs modified the conclusion from BoE of RCTs in nearly 50% of the associations, although the direction of effect was mainly concordant between BoE of RCTs and pooled estimates. Our findings provide insights for the potential impact of pooling both BoE in Cochrane nutrition reviews. CSs should be considered for inclusion in future Cochrane nutrition reviews, and we recommend analyzing RCTs and CSs in separate meta-analyses, or, if combined together, with a subgroup analysis.

Impact of α-Linolenic Acid, the Vegetable ω-3 Fatty Acid, on Cardiovascular Disease and Cognition

Given the evidence of the health benefits of plant-based diets and long-chain n-3 (ω-3) fatty acids, there is keen interest in better understanding the role of α-linolenic acid (ALA), a plant-derived n-3 fatty acid, on cardiometabolic diseases and cognition. There is increasing evidence for ALA largely based on its major food sources (i.e., walnuts and flaxseed); however, this lags behind our understanding of long-chain n-3 fatty acids. Meta-analyses of observational studies have shown that increasing dietary ALA is associated with a 10% lower risk of total cardiovascular disease and a 20% reduced risk of fatal coronary heart disease. Three randomized controlled trials (RCTs) [AlphaOmega trial, Prevención con Dieta Mediterránea (PREDIMED) trial, and Lyon Diet Heart Study] all showed benefits of diets high in ALA on cardiovascular-related outcomes, but the AlphaOmega trial, designed to specifically evaluate ALA effects, only showed a trend for benefit. RCTs have shown that dietary ALA reduced total cholesterol, LDL cholesterol, triglycerides, and blood pressure, and epidemiologic studies and some trials also have shown an anti-inflammatory effect of ALA, which collectively account for, in part, the cardiovascular benefits of ALA. A meta-analysis reported a trend toward diabetes risk reduction with both dietary and biomarker ALA. For metabolic syndrome and obesity, the evidence for ALA benefits is inconclusive. The role of ALA in cognition is in the early stages but shows promising evidence of counteracting cognitive impairment. Much has been learned about the health benefits of ALA and with additional research we will be better positioned to make strong evidence-based dietary recommendations for the reduction of many chronic diseases.

Dietary Intake and Biomarkers of α-Linolenic Acid and Mortality: A Meta-Analysis of Prospective Cohort Studies

Background: The association between α-linolenic acid (ALA) and mortality is inconsistent and has not been summarized systematically.

Objective: The purpose was to conduct a meta-analysis that synthesized the results of prospective cohort studies to investigate associations between ALA intake and mortality.

Methods: We conducted a comprehensive search on PubMed, Embase, and Web of Science databases on May 1, 2021, for relevant prospective cohort studies which reported associations of ALA (assessed by dietary surveys and/or ALA concentrations in body tissues) with mortality from all-cause, cardiovascular disease (CVD), and other diseases. Multivariable-adjusted relative risks (RRs) were pooled by a random or fixed-effects model.

Results: A total of 34 prospective cohort studies, of which 17 reported dietary ALA intake, 14 for ALA biomarkers, and the remaining 3 reported both of intake and biomarkers. The studies included 6,58,634 participants, and deaths were classified into all-cause mortality (56,898), CVD mortality (19,123), and other diseases mortality (19,061). Pooled RRs of ALA intake were 0.93 (95% CI: 0.86, 1.01, I² = 71.2%) for all-cause mortality, 0.90 (95% CI: 0.83, 0.98, I² = 22.1%) for CVD mortality, and 0.94 (95% CI: 0.83, 1.06, I² = 73.3%) for other diseases mortality. The two-stage random-effects dose-response analysis showed a linear relationship between dietary ALA intake and CVD-mortality and each 0.5% energy increment of ALA intake was associated with a 5% lower risk of CVD-mortality (RR: 0.95; 95% CI: 0.90, 1.00). Pooled RRs per SD increment of ALA biomarkers were 0.99 (95% CI: 0.96, 1.01, I² = 27%) for all-cause mortality, 1.00 (95% CI: 0.98, 1.03, I² = 0%) for CVD mortality and 0.98 (95% CI: 0.95, 1.01, I² = 0%) for other diseases mortality.

Conclusions: This meta-analysis summarizing the available prospective cohort studies indicated that ALA intake was associated with reduced risk of mortality, especially CVD mortality. Our findings suggest that ALA consumption may be beneficial for death prevention. Systematic Review Registration:https://www.crd.york.ac.uk/PROSPERO; identifier: CRD42021264532.

Dietary intake and biomarkers of alpha linolenic acid and risk of all cause, cardiovascular, and cancer mortality: systematic review and dose-response meta-analysis of cohort studies

OBJECTIVE

To examine the associations between dietary intake and tissue biomarkers of alpha linolenic acid (ALA) and risk of mortality from all causes, cardiovascular disease (CVD), and cancer.

DESIGN

Systematic review and meta-analysis of prospective cohort studies.

DATA SOURCES

PubMed, Scopus, ISI Web of Science, and Google Scholar to 30 April 2021.

STUDY SELECTION

Prospective cohort studies that reported the risk estimates for death from all causes, CVD, and cancer.

DATA SYNTHESIS

Summary relative risks and 95% confidence intervals were calculated for the highest versus lowest categories of ALA intake using random effects and fixed effects models. Linear and non-linear dose-response analyses were conducted to assess the dose-response associations between ALA intake and mortality.

RESULTS

41 articles from prospective cohort studies were included in this systematic review and meta-analysis, totalling 1 197 564 participants. During follow-up ranging from two to 32 years, 198 113 deaths from all causes, 62 773 from CVD, and 65 954 from cancer were recorded. High intake of ALA compared with low intake was significantly associated with a lower risk of deaths from all causes (pooled relative risk 0.90, 95% confidence interval 0.83 to 0.97, I2=77.8%, 15 studies), CVD (0.92, 0.86 to 0.99, I2=48.2%, n=16), and coronary heart disease (CHD) (0.89, 0.81 to 0.97, I2=5.6%, n=9), and a slightly higher risk of cancer mortality (1.06, 1.02 to 1.11, I2=3.8%, n=10). In the dose-response analysis, a 1 g/day increase in ALA intake (equivalent to one tablespoon of canola oil or 0.5 ounces of walnut) was associated with a 5% lower risk of all cause (0.95, 0.91 to 0.99, I2=76.2%, n=12) and CVD mortality (0.95, 0.91 to 0.98, I2=30.7%, n=14). The pooled relative risks for the highest compared with lowest tissue levels of ALA indicated a significant inverse association with all cause mortality (0.95, 0.90 to 0.99, I2=8.2%, n=26). Also, based on the dose-response analysis, each 1 standard deviation increment in blood concentrations of ALA was associated with a lower risk of CHD mortality (0.92, 0.86 to 0.98, I2=37.1%, n=14).

CONCLUSIONS

The findings show that dietary ALA intake is associated with a reduced risk of mortality from all causes, CVD, and CHD, and a slightly higher risk of cancer mortality, whereas higher blood levels of ALA are associated with a reduced risk of all cause and CHD mortality only.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42021229487.

The review of alpha-linolenic acid: Sources, metabolism, and pharmacology

α-linolenic acid (ALA, 18:3n-3) is a carboxylic acid composed of 18 carbon atoms and three cis double bonds, and is an essential fatty acid indispensable to the human body. This study aims to systematically review related studies on the dietary sources, metabolism, and pharmacological effects of ALA. Information on ALA was collected from the internet database PubMed, Elsevier, ResearchGate, Web of Science, Wiley Online Library, and Europe PMC using a combination of keywords including "pharmacology," "metabolism," "sources." The following findings are mainly contained. (a) ALA can only be ingested from food and then converted into eicosapentaenoic acid and docosahexaenoic acid in the body. (b) This conversion process is relatively limited and affected by many factors such as dose, gender, and disease. (c) Pharmacological research shows that ALA has the anti-metabolic syndrome, anticancer, antiinflammatory, anti-oxidant, anti-obesity, neuroprotection, and regulation of the intestinal flora properties. (d) There are the most studies that prove ALA has anti-metabolic syndrome effects, including experimental studies and clinical trials. (e) The therapeutic effect of ALA will be affected by the dosage. In short, ALA is expected to treat many diseases, but further high quality studies are needed to firmly establish the clinical efficacy of ALA.

Evaluating agreement between bodies of evidence from randomised controlled trials and cohort studies in nutrition research: meta-epidemiological study

OBJECTIVE

To evaluate the agreement between diet-disease effect estimates of bodies of evidence from randomised controlled trials and those from cohort studies in nutrition research, and to investigate potential factors for disagreement.

DESIGN

Meta-epidemiological study.

DATA SOURCES

Cochrane Database of Systematic Reviews, and Medline.

REVIEW METHODS

Population, intervention or exposure, comparator, outcome (PI/ECO) elements from a body of evidence from cohort studies (BoE(CS)) were matched with corresponding elements of a body of evidence from randomised controlled trials (BoE(RCT)). Pooled ratio of risk ratios or difference of mean differences across all diet-disease outcome pairs were calculated. Subgroup analyses were conducted to explore factors for disagreement. Heterogeneity was assessed through I2 and τ2. Prediction intervals were calculated to assess the range of possible values for the difference in the results between evidence from randomised controlled trials and evidence from cohort studies in future comparisons.

RESULTS

97 diet-disease outcome pairs (that is, matched BoE(RCT) and BoE(CS)) were identified overall. For binary outcomes, the pooled ratio of risk ratios comparing estimates from BoE(RCT) with BoE(CS) was 1.09 (95% confidence interval 1.04 to 1.14; I2=68%; τ2=0.021; 95% prediction interval 0.81 to 1.46). The prediction interval indicated that the difference could be much more substantial, in either direction. We further explored heterogeneity and found that PI/ECO dissimilarities, especially for the comparisons of dietary supplements in randomised controlled trials and nutrient status in cohort studies, explained most of the differences. When the type of intake or exposure between both types of evidence was identical, the estimates were similar. For continuous outcomes, small differences were observed between randomised controlled trials and cohort studies.

CONCLUSION

On average, the difference in pooled results between estimates from BoE(RCT) and BoE(CS) was small. But wide prediction intervals and some substantial statistical heterogeneity in cohort studies indicate that important differences or potential bias in individual comparisons or studies cannot be excluded. Observed differences were mainly driven by dissimilarities in population, intervention or exposure, comparator, and outcome. These findings could help researchers further understand the integration of such evidence into prospective nutrition evidence syntheses and improve evidence based dietary guidelines.

Composition of Dietary Fatty Acids and Health Risks in Japanese Youths

In the overall composition of dietary fatty acids (FAs), the quantity of each FA is interrelated with that of others. We examined the associations between dietary FA composition and cardiometabolic risk in Japanese youths. Risk factors (anthropometric characteristics, serum lipid and liver enzyme levels, and blood pressure) were measured in 5485 junior-high-school students. Dietary intake was assessed using a food frequency questionnaire. The mean saturated FA (SFA), monounsaturated FA (MUFA), omega-6 polyunsaturated FAs (PUFAs), and omega-3 PUFAs intake were 9.6%E, 10.3%E, 6.3%E, and 1.1%E, respectively. In compositional regression analysis controlled for confounders, a high intake of omega-6 PUFAs relative to others was associated with low low-density-lipoprotein cholesterol levels (LDL-C; p = 0.003), and relative SFA intake was associated with high levels of gamma-glutamyl transpeptidase (p = 0.019). Relative omega-3 PUFAs intake was associated with low blood pressure (p = 0.005–0.034) but had unfavorable effects on adiposity and alanine transaminase. Substitutional models showed similar results for omega-6 PUFAs on LDL-C, but MUFA had inconsistent effects on risk factors. The results from the compositional data analysis were consistent with previous studies and clinical practice/knowledge. Focusing on increasing omega-6 PUFAs in Japanese youths could have favorable consequences in the long term.

Dietary fatty acids and CHD: from specific recommendations to dietary patterns

Several countries have issued dietary recommendations about total and specific fatty acid (FA) intake for the prevention of CHD. For many years until today, controversies have existed especially about the deleterious effect or not of SFA, and the protective effect or not of n-3 PUFA, so that some authors have criticised these recommendations. There are many reasons for these controversies, including the different conclusions of prospective cohort studies compared with randomised clinical trials (RCT), and the contradictory conclusions of meta-analyses depending on the quality, number and type of studies included. The interrelationships between different FA in the diet make it difficult to analyse the specific effect of a particular class of FA on CHD. Furthermore, based on clinical practice and effectiveness of population-based prevention, it is very difficult at the individual level to assess in personal dietary intake the actual percentage and/or amount of SFA contained in each meal or consumed daily/weekly. In this critical narrative review, we try to answer the question of whether it would not be more relevant, in 2020, to promote dietary patterns, rather than FA intake recommendations. We critically analyse past and recent data on the association of FA with CHD, then propose that the Mediterranean diet and Japanese diet should be revitalised for Westerners and Asian populations, respectively. This does not exclude the usefulness of continuing research about effects of FA towards CHD, and accepting that what seems true today might be revised, at least partially tomorrow.

Intake and metabolism of omega-3 and omega-6 polyunsaturated fatty acids: nutritional implications for cardiometabolic diseases

Prospective observational studies support the use of long-chain omega-3 polyunsaturated fatty acids (PUFAs) in the primary prevention of atherosclerotic cardiovascular disease; however, randomised controlled trials, have often reported neutral findings. There is a long history of debate about the potential harmful effects of a high intake of omega-6 PUFAs, although this idea is not supported by prospective observational studies or randomised controlled trials. Health effects of PUFAs might be influenced by Δ-5 and Δ-6 desaturases, the key enzymes in the metabolism of PUFAs. The activity of these enzymes and modulation by variants in encoding genes (FADS1-2-3 gene cluster) are linked to several cardiometabolic traits. This Review will further consider non-genetic determinants of desaturase activity, which have the potential to modify the availability of PUFAs to tissues. Finally, we discuss the consequences of altered desaturase activity in the context of PUFA intake, that is, gene-diet interactions and their clinical and public health implications.

Time Course and Sex Effects of α-Linolenic Acid-Rich and DHA-Rich Supplements on Human Plasma Oxylipins: A Randomized Double-Blind Crossover Trial

BACKGROUND

Differences in health effects of dietary α-linolenic acid (ALA) and DHA are mediated at least in part by differences in their effects on oxylipins.

OBJECTIVES

Time course and sex differences of plasma oxylipins in response to ALA- compared with DHA-rich supplements were examined.

METHODS

Healthy men and women, aged 19-34 y and BMI 18-28 kg/m2, were provided with capsules containing ∼4 g/d of ALA or DHA in a randomized double-blind crossover study with >6-wk wash-in and wash-out phases. Plasma PUFA and oxylipin (primary outcome) concentrations at days 0, 1, 3, 7, 14, and 28 of supplementation were analyzed by GC and HPLC-MS/MS, respectively. Sex differences, supplementation and time effects, and days to plateau were analyzed.

RESULTS

ALA supplementation doubled ALA concentrations, but had no effects on ALA oxylipins after 28 d, whereas DHA supplementation tripled both DHA and its oxylipins. Increases in DHA oxylipins were detected as early as day 1, and a plateau was reached by days 5-7 for 11 of 12 individual DHA oxylipins and for total DHA oxylipins. Nine individual DHA oxylipins reached a plateau in females with DHA supplementation, compared with only 4 in males. A similar time course and sex difference pattern occurred with EPA and its oxylipins with DHA supplementation. DHA compared with ALA supplementation also resulted in higher concentrations of 4 individual arachidonic acids, 1 linoleic acid, and 1 dihomo-γ-linolenic acid oxylipin, despite not increasing the concentrations of these fatty acids, further demonstrating that oxylipins do not always reflect their precursor PUFA.

CONCLUSIONS

DHA compared with a similar dose of ALA has greater effects on both n-3 and n-6 oxylipins in young, healthy adults, with differences in response to DHA supplementation occurring earlier and being greater in females. These findings can help explain differences in dietary effects of ALA and DHA.This study was registered at clinicaltrials.gov as NCT02317588.

Erythrocyte Membrane Polyunsaturated Fatty Acids Are Associated with Incidence of Metabolic Syndrome in Middle-Aged and Elderly People-An 8.8-Year Prospective Study

BACKGROUND

The total and specific types of polyunsaturated fatty acids (PUFAs) related to metabolic syndrome (MetS) remain inconsistent.

OBJECTIVE

We assessed the association of erythrocyte n-3 and n-6 PUFAs with MetS and the components of MetS in a cohort population.

METHODS

This prospective analysis included 2754 participants (aged 40-75 y) from the Guangzhou Nutrition and Health Study (2008-2019) in China. Erythrocyte PUFAs at baseline were measured using gas chromatography. MetS was assessed every 3 y according to the updated National Cholesterol Education Program Adult Treatment Panel III criteria. Multivariable Cox proportional hazard models were used to evaluate HRs and 95% CIs.

RESULTS

We identified 716 incident cases of MetS. The primary analyses showed that the HRs (95% CIs) of MetS (tertile 3 versus 1) were 0.67 (0.56, 0.80) for n-3 PUFAs and 0.70 (0.58, 0.85) for n-6 PUFAs (all Ps trend <0.001). The secondary outcomes showed that, higher erythrocyte very-long-chain (VLC) PUFAs [20:3n-3, docosapentaenoic acid (DPA), docosahexaenoic acid (DHA), arachidonic acid (ARA), and 22:4n-6], but lower α-linolenic acid (ALA) and γ-linolenic acid (GLA), tended to be associated with lower incidences of MetS and its components; among individual MetS components, the associations of PUFAs were more pronounced for hypertriglyceridemia (HTG) and hypertension, followed by low high-density lipoproten (HDL) cholesterol. Significantly higher concentrations of n-3 PUFAs (total, DPA, and DHA) and n-6 PUFAs (total, ARA, and 22:4) were observed in participants with improved (versus progressed) status of MetS (all Ps trend ≤0.003).

CONCLUSION

This study reveals that higher erythrocyte VLC n-3 and n-6 PUFAs, but lower 18-carbon PUFAs (ALA and GLA), are associated with lower risks of MetS components (HTG, hypertension, and low HDL cholesterol) and thereby lower MetS incidence in Chinese adults.

Comparative exploration of free fatty acids in donkey colostrum and mature milk based on a metabolomics approach

Donkey milk is an ideal substitute for human milk owing to its similar composition. Nevertheless, changes in the composition and related metabolic pathways of free fatty acids (FFA) in donkey milk between colostrum and mature milk have not been studied well. In this study, metabolomic methods based on gas chromatography tandem time-of-flight mass spectrometry (GC-TOF-MS) were used to explore and compare FFA in donkey colostrum (DC) and mature milk (DMM). A total of 24 FFA were characterized and quantified in DC and in DMM. Of these, 11 FFA differed significantly between DC and DMM, and there were 6 key differential metabolic pathways. These results demonstrated that the composition of FFA in donkey milk changed with lactation stage. The interactions and metabolic pathways were further analyzed to explore the mechanisms that altered the milk composition during lactation. Our results provide insights into the changes in milk of the nonruminant mammals during lactation. The results provide practical information for the development of donkey milk products and a foundation for future research on specific milk nutrients.

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.

Association between erythrocyte membrane n-3 and n-6 polyunsaturated fatty acids and carotid atherosclerosis: A prospective study

BACKGROUND AND AIMS

The relationship of polyunsaturated fatty acids (PUFAs) with cardiovascular risk is still controversial. We aimed to determine whether erythrocyte n-3 and n-6 PUFAs are related to the risk of carotid atherosclerosis.

METHODS

From 2008 to 2019, baseline erythrocyte n-3 and n-6 PUFAs were determined in a cohort of 4040 Chinese adults (40-75 ys). The intima-media thickness (IMT) at the common carotid artery (CCA) and bifurcation of the carotid artery (BIF) and carotid plaque were assessed using ultrasonography at baseline and every 3 years.

RESULTS

During a median follow-up of 8.8 years, we identified the following newly diagnosed cases: 535 cases of CCAIMT thickening, 654 cases of BIFIMT thickening, and 850 cases of carotid plaque. Higher erythrocyte docosahexaenoic acid (DHA) and arachidonic acid (ARA) and lower gamma-linolenic acid (GLA) were associated with decreased risks of BIFIMT thickening. N-3 eicosatrienoic acid (ETrA), docosapentaenoic acid (DPA), and n-6 dodecylthioacetic acid (DTA) presented a significant beneficial association with carotid IMT thickening in the short-term (2.8 y) follow-up (all p trend <0.02), although the association was attenuated in the relatively long-term (8.8 y) follow-up. In addition, carotid plaque risk was found to be inversely associated with ETrA and DHA but positively associated with alpha-linolenic acid (ALA). N-6 linolenic acid (LA) and eicosadienoic acid (EDA) were not significantly associated with carotid atherosclerosis risk.

CONCLUSIONS

Higher erythrocyte very-long-chain n-3 and n-6 PUFAs (especially DHA and ARA) and lower erythrocyte GLA are associated with lower carotid atherosclerosis risk, suggesting potential cardioprotective roles of very-long-chain PUFAs.

Polarization of Macrophages in Human Adipose Tissue is Related to the Fatty Acid Spectrum in Membrane Phospholipids

Residential macrophages in adipose tissue play a pivotal role in the development of inflammation not only within this tissue, but also affect the proinflammatory status of the whole body. Data on human adipose tissue inflammation and the role of macrophages are rather scarce. We previously documented that the proportion of proinflammatory macrophages in human adipose tissue correlates closely with non-HDL cholesterol concentrations. We hypothesized that this is due to the identical influence of diet on both parameters and decided to analyze the fatty acid spectrum in cell membrane phospholipids of the same individuals as a parameter of the diet consumed. Proinflammatory and anti-inflammatory macrophages were isolated from human adipose tissue (n = 43) and determined by flow cytometry as CD14+CD16+CD36^high and CD14+CD16−CD163+, respectively. The spectrum of fatty acids in phospholipids in the cell membranes of specimens of the same adipose tissue was analyzed, and the proportion of proinflammatory macrophage increased with the proportions of palmitic and palmitoleic acids. Contrariwise, these macrophages decreased with increasing alpha-linolenic acid, total n-3 fatty acids, n-3/n-6 ratio, and eicosatetraenoic acid. A mirror picture was documented for the proportion of anti-inflammatory macrophages. The dietary score, obtained using a food frequency questionnaire, documented a positive relation to proinflammatory macrophages in individuals who consumed predominantly vegetable fat and fish, and individuals who consumed diets based on animal fat without fish and nut consumption. he present data support our hypothesis that macrophage polarization in human visceral adipose tissue is related to fatty acid metabolism, cell membrane composition, and diet consumed. It is suggested that fatty acid metabolism might participate also in inflammation and the risk of developing cardiovascular disease.

Marine and plant-based n-3 PUFA and atherosclerotic cardiovascular disease

n-3 PUFA may exert favourable effects on several processes that may inhibit the atherosclerotic process. However, the role of n-3 PUFA in lowering the risk of atherosclerotic CVD (ASCVD) has been fiercely debated. In the present paper, we summarise the main findings from previous follow-up studies of intake and studies using adipose tissue as an objective biomarker to investigate exposure to n-3 PUFA in relation to ASCVD risk and discuss some perspectives for further research. The majority of previous studies investigating intake of marine- and plant-based n-3 PUFA have focused on CHD while other ASCVD such as ischaemic stroke and peripheral artery disease have been less studied. However, recent data from Danish Diet, Cancer and Health cohort suggest that marine n-3 PUFA may be inversely associated with risk of myocardial infarction, ischaemic stroke and peripheral arterial disease caused by atherosclerosis. The effect of the plant-derived n-3 PUFA α-linolenic acid on ASCVD is less clear and several gaps in the literature remain to be explored.