EFFECT OF LINOLENIC ACID UPON THE METABOLISM OF LINOLEIC ACID

Arachidonic acid in aging: New roles for old players

BACKGROUND

Arachidonic acid (AA), one of the most ubiquitous polyunsaturated fatty acids (PUFAs), provides fluidity to mammalian cell membranes. It is derived from linoleic acid (LA) and can be transformed into various bioactive metabolites, including prostaglandins (PGs), thromboxanes (TXs), lipoxins (LXs), hydroxy-eicosatetraenoic acids (HETEs), leukotrienes (LTs), and epoxyeicosatrienoic acids (EETs), by different pathways. All these processes are involved in AA metabolism. Currently, in the context of an increasingly visible aging world population, several scholars have revealed the essential role of AA metabolism in osteoporosis, chronic obstructive pulmonary disease, and many other aging diseases.

AIM OF REVIEW

Although there are some reviews describing the role of AA in some specific diseases, there seems to be no or little information on the role of AA metabolism in aging tissues or organs. This review scrutinizes and highlights the role of AA metabolism in aging and provides a new idea for strategies for treating aging-related diseases.

KEY SCIENTIFIC CONCEPTS OF REVIEW

As a member of lipid metabolism, AA metabolism regulates the important lipids that interfere with the aging in several ways. We present a comprehensivereviewofthe role ofAA metabolism in aging, with the aim of relieving the extreme suffering of families and the heavy economic burden on society caused by age-related diseases. We also collected and summarized data on anti-aging therapies associated with AA metabolism, with the expectation of identifying a novel and efficient way to protect against aging.

Complexity of understanding the role of dietary and erythrocyte docosahexaenoic acid (DHA) on the cognitive performance of school-age children

Background

Early childhood is a period of rapid brain development, with increases in synapses rich in the omega-3 (ω-3) fatty acid, DHA (22:6ω-3) continuing well beyond infancy. Despite the importance of DHA to neural phospholipids, the requirement of dietary DHA for neurodevelopment remains unclear.

Objectives

The aim was to assess the dietary DHA and DHA status of young children, and determine the association with cognitive performance.

Methods

This was a cross-sectional study of healthy children (5-6 y), some of whom were enrolled in a follow-up of a clinical trial (NCT00620672). Dietary intake data (n = 285) were assessed with a food-frequency questionnaire (FFQ) and three 24-h recalls. Family characteristics were collected by questionnaire, and anthropometric data measured. Venous blood was collected, cognitive performance assessed using several age-appropriate tools including the Kaufman Assessment Battery for Children. The relation between dietary DHA, RBC DHA, and child neurodevelopment test scores was determined using Pearson's correlation or Spearman's rho, and quintiles of test scores compared by Mann-Whitney U test.

Results

Child DHA intakes were highly variable, with a stronger association between RBC DHA and DHA intake assessed by FFQ (rho = 0.383, P < 0.001) compared with one or three 24-h recalls. Observed ethnic differences in DHA intake status as well as neurodevelopmental test scores led to analysis of the association between DHA intake and status with neurodevelopment test scores for White children only (n = 190). Child RBC DHA status was associated with neurodevelopment test scores, including language (rho = 0.211, P = 0.009) and short-term memory (rho = 0.187, P = 0.019), but only short-term memory was associated with dietary DHA (rho = 0.221, P = 0.003).

Conclusions

Child RBC DHA but not dietary DHA was associated with multiple tests of cognitive performance. In addition, DHA intake was only moderately associated with RBC DHA, raising complex questions on the relation between diet, DHA transfer to membrane lipids, and neural function.

Neurodevelopment, nutrition and genetics. A contemporary retrospective on neurocognitive health on the occasion of the 100th anniversary of the National Institute of Nutrition, Hyderabad, India

In celebration of the centenary of the National Institute of Nutrition (NIN), Hyderabad, India (1918-2018), a symposium highlighted the progress in nutrition knowledge made over the century, as well as major gaps in implementation of that knowledge. Brain famine caused by a shortage of nutrients required for perinatal brain development has unfortunately become a global reality, even as protein-calorie famine was largely averted by the development of high yield crops. While malnutrition remains widespread, the neglect of global food policies that support brain development and maintenance are most alarming. Brain disorders now top the list of the global burden of disease, even with obesity rising throughout the world. Neurocognitive health, remarkably, is seldom listed among the non-communicable diseases (NCDs) and is therefore seldom considered as a component of food policy. Most notably, the health of mothers before conception and through pregnancy as mediated by proper nutrition has been neglected by the current focus on early death in non-neurocognitive NCDs, thereby compromising intellectual development of the ensuing generations. Foods with balanced essential fatty acids and ample absorbable micronutrients are plentiful for populations with access to shore-based foods, but deficient only a few kilometres away from the sea. Sustained access to brain supportive foods is a priority for India and throughout the world to enable each child to develop to their intellectual potential, and support a prosperous, just, and peaceful world. Nutrition education and food policy should place the nutritional requirements for the brain on top of the list of priorities.

Interpreting Clinical Trials With Omega-3 Supplements in the Context of Ancestry and FADS Genetic Variation

Human diets in developed countries such as the US have changed dramatically over the past 75 years, leading to increased obesity, inflammation, and cardiometabolic dysfunction. Evidence over the past decade indicates that the interaction of genetic variation with changes in the intake of 18-carbon essential dietary omega-6 (n-6) and omega-3 (n-3) polyunsaturated fatty acids (PUFA), linoleic acid (LA) and α-linolenic acid (ALA), respectively, has impacted numerous molecular and clinical phenotypes. Interactions are particularly relevant with the FADS1 and FADS2 genes, which encode key fatty acid desaturases in the pathway that converts LA and ALA to their long chain (≥20 carbons), highly unsaturated fatty acid (HUFA) counterparts. These gene by nutrient interactions affect the levels and balance of n-6 and n-3 HUFA that in turn are converted to a wide array of lipids with signaling roles, including eicosanoids, docosanoids, other oxylipins and endocannabinoids. With few exceptions, n-6 HUFA are precursors of pro-inflammatory/pro-thrombotic signaling lipids, and n-3 HUFA are generally anti-inflammatory/anti-thrombotic. We and others have demonstrated that African ancestry populations have much higher frequencies (vs. European-, Asian- or indigenous Americas-ancestry populations) of a FADS “derived” haplotype that is associated with the efficient conversion of high levels of dietary n-6 PUFA to pro-inflammatory n-6 HUFA. By contrast, an “ancestral” haplotype, carrying alleles associated with a limited capacity to synthesize HUFA, which can lead to n-3 HUFA deficiency, is found at high frequency in certain Hispanic populations and is nearly fixed in several indigenous populations from the Americas. Based on these observations, a focused secondary subgroup analysis of the VITAL n-3 HUFA supplementation trial stratifying the data based on self-reported ancestry revealed that African Americans may benefit from n-3 HUFA supplementation, and both ancestry and FADS variability should be factored into future clinical trials design.

Tissue-Specific Content of Polyunsaturated Fatty Acids in (n-3) Deficiency State of Rats

The dietary intake of fatty acids (FAs) affects the composition and distribution of FAs in the body. Here, a first-generation (n-3)-deficiency study was conducted by keeping young (age 21 ± 2 days) Sprague-Dawley male rats on a peanut-oil-based diet for 33 days after weaning in order to compare the effect of mild (n-3)-deficiency on the lipid composition of different organs and feces. Soybean-oil-based diet was used as a control. The plasma FA levels corresponded to FAs levels in the organs. Lower docosahexaenoic acid (DHA) content was detected in the plasma, brain, testis, visceral fat, heart, and lungs of the (n-3)-deficient group, whereas the DHA content of the eye and feces did not differ between the experimental groups. The DHA content of the brains of the (n-3)-deficient group was 86% of the DHA content of the brains of the (n-3)-adequate group. The DHA level of the organs was affected in the order of visceral fat > liver triacylglycerols > lung > heart > liver phospholipids > testis > eye > brain, with brain being least affected. The low levels of (n-3) FAs in the liver, brain, eye, heart, and lung were offset by an increase in the (n-6) FAs, mainly arachidonic acid. These results indicate that, in rats, adequate maternal nutrition during pregnancy and weaning does not provide enough (n-3) FAs for 33 days of an (n-3)-deficient diet. Results of this study can be used also to evaluate the conditions needed to reach mild (n-3) deficiency in the first generation of rats and to evaluate the feasibility to collect data from a variety of organs or only selected ones.

Reducing Disease Activity of Inflammatory Bowel Disease by Consumption of Plant-Based Foods and Nutrients

Inflammatory bowel disease is a chronic and recurring inflammatory condition of the gastrointestinal tract encompassing ulcerative colitis and Crohn's disease. Although the pathogenesis of inflammatory bowel disease remains to be fully elucidated, environmental factors such as diet are believed to play a pivotal role in the onset and management of inflammatory bowel disease. Diet is thought to play an essential role in intestinal inflammation due to its regulatory effects on the microbiota, gut immune system, and epithelial barrier function. Although the evidence remains insufficient to draw firm conclusions on the role of specific dietary components in gastrointestinal diseases, studies have suggested that a Western diet with high intakes of total fats, omega-6 fatty acids, and meat have been associated with intestinal inflammation and relapse of inflammatory bowel disease. In contrast to a Western diet, plant-based diets often result in a reduced intake of total fats and meats and an increased intake of plant fibers which may contribute to reduced intestinal inflammation. This review critically examines the influence of plant-based dietary components on the clinical disease course of inflammatory bowel disease. Furthermore, this review discusses the benefits and possible limitations of plant-derived dietary components in the treatment of inflammatory bowel disease while addressing the principal type of disease and the anatomic site of inflammation within the gastrointestinal tract. Finally, this review points out important directions for future research on the role of diet in inflammatory bowel disease. A better understanding of the role of diet and intestinal inflammation may pave the way for novel dietary interventions and specific foods- or food supplements, which can support the treatment of inflammatory bowel disease.

Impact of Amerind ancestry and FADS genetic variation on omega-3 deficiency and cardiometabolic traits in Hispanic populations

Long chain polyunsaturated fatty acids (LC-PUFAs) have critical signaling roles that regulate dyslipidemia and inflammation. Genetic variation in the FADS gene cluster accounts for a large portion of interindividual differences in circulating and tissue levels of LC-PUFAs, with the genotypes most strongly predictive of low LC-PUFA levels at strikingly higher frequencies in Amerind ancestry populations. In this study, we examined relationships between genetic ancestry and FADS variation in 1102 Hispanic American participants from the Multi-Ethnic Study of Atherosclerosis. We demonstrate strong negative associations between Amerind genetic ancestry and LC-PUFA levels. The FADS rs174537 single nucleotide polymorphism (SNP) accounted for much of the AI ancestry effect on LC-PUFAs, especially for low levels of n-3 LC-PUFAs. Rs174537 was also strongly associated with several metabolic, inflammatory and anthropomorphic traits including circulating triglycerides (TGs) and E-selectin in MESA Hispanics. Our study demonstrates that Amerind ancestry provides a useful and readily available tool to identify individuals most likely to have FADS-related n-3 LC-PUFA deficiencies and associated cardiovascular risk.

Perspective: Moving Toward Desirable Linoleic Acid Content in Infant Formula

Infant formula should provide the appropriate nutrients and adequate energy to facilitate healthy infant growth and development. If conclusive data on quantitative nutrient requirements are not available, the composition of human milk (HM) can provide some initial guidance on the infant formula composition. This paper provides a narrative review of the current knowledge, unresolved questions, and future research needs in the area of HM fatty acid (FA) composition, with a particular focus on exploring appropriate intake levels of the essential FA linoleic acid (LA) in infant formula. The paper highlights a clear gap in clinical evidence as to the impact of LA levels in HM or formula on infant outcomes, such as growth, development, and long-term health. The available preclinical information suggests potential disadvantages of high LA intake in the early postnatal period. We recommend performing well-designed clinical intervention trials to create clarity on optimal levels of LA to achieve positive impacts on both short-term growth and development and long-term functional health outcomes.

Fatty Acid Desaturase 1 Influences Hepatic Lipid Homeostasis by Modulating the PPARα-FGF21 Axis

The fatty acid desaturase 1 (FADS1), also known as delta-5 desaturase (D5D), is one of the rate-limiting enzymes involved in the desaturation and elongation cascade of polyunsaturated fatty acids (PUFAs) to generate long-chain PUFAs (LC-PUFAs). Reduced function of D5D and decreased hepatic FADS1 expression, as well as low levels of LC-PUFAs, were associated with nonalcoholic fatty liver disease. However, the causal role of D5D in hepatic lipid homeostasis remains unclear. In this study, we hypothesized that down-regulation of FADS1 increases susceptibility to hepatic lipid accumulation. We used in vitro and in vivo models to test this hypothesis and to delineate the molecular mechanisms mediating the effect of reduced FADS1 function. Our study demonstrated that FADS1 knockdown significantly reduced cellular levels of LC-PUFAs and increased lipid accumulation and lipid droplet formation in HepG2 cells. The lipid accumulation was associated with significant alterations in multiple pathways involved in lipid homeostasis, especially fatty acid oxidation. These effects were demonstrated to be mediated by the reduced function of the peroxisome proliferator-activated receptor alpha (PPARα)-fibroblast growth factor 21 (FGF21) axis, which can be reversed by treatment with docosahexaenoic acid, PPARα agonist, or FGF21. In vivo, FADS1-knockout mice fed with high-fat diet developed increased hepatic steatosis as compared with their wild-type littermates. Molecular analyses of the mouse liver tissue largely corroborated the observations in vitro, especially along with reduced protein expression of PPARα and FGF21. Conclusion: Collectively, these results suggest that dysregulation in FADS1 alters liver lipid homeostasis in the liver by down-regulating the PPARα-FGF21 signaling axis.

Polyunsaturated fatty acid biosynthesis pathway and genetics. implications for interindividual variability in prothrombotic, inflammatory conditions such as COVID-19✰,✰✰,★,★★

COVID-19 symptoms vary from silence to rapid death, the latter mediated by both a cytokine storm and a thrombotic storm. SARS-CoV (2003) induces Cox-2, catalyzing the synthesis, from highly unsaturated fatty acids (HUFA), of eicosanoids and docosanoids that mediate both inflammation and thrombosis. HUFA balance between arachidonic acid (AA) and other HUFA is a likely determinant of net signaling to induce a healthy or runaway physiological response. AA levels are determined by a non-protein coding regulatory polymorphisms that mostly affect the expression of FADS1, located in the FADS gene cluster on chromosome 11. Major and minor haplotypes in Europeans, and a specific functional insertion-deletion (Indel), rs66698963, consistently show major differences in circulating AA (>50%) and in the balance between AA and other HUFA (47-84%) in free living humans; the indel is evolutionarily selective, probably based on diet. The pattern of fatty acid responses is fully consistent with specific genetic modulation of desaturation at the FADS1-mediated 20:3→20:4 step. Well established principles of net tissue HUFA levels indicate that the high linoleic acid and low alpha-linoleic acid in populations drive the net balance of HUFA for any individual. We predict that fast desaturators (insertion allele at rs66698963; major haplotype in Europeans) are predisposed to higher risk and pathological responses to SARS-CoV-2 could be reduced with high dose omega-3 HUFA.

Dynamic interactions of n-3 and n-6 fatty acid nutrients

Careful handling of data on fatty acid composition is needed when interpreting evidence for the influence of dietary n-3 and n-6 essential fatty acids on brain function and health conditions. The relative dietary supplies of competing n-3 and n-6 nutrients determine the balance of 20- and 22-carbon n-3 and n-6 highly unsaturated fatty acids (HUFA) which accumulate competitively at the 2-position of tissue phospholipids. In turn, the HUFA balance expressed as the %n-6 in HUFA affects the likely intensity of n-6 eicosanoid actions in diverse health conditions. As a result, measures of HUFA balance are important, valid biomarkers for designing and monitoring successful preventive nutrition interventions. Successful interventions must also consider the ability of fatty acid ligands to saturate binding sites of enzymes and receptors and give paradoxical dose-response results.

Validation of an equation predicting highly unsaturated fatty acid (HUFA) compositions of human blood fractions from dietary intakes of both HUFAs and their precursors

Proportions of omega-3 (n-3) and omega-6 (n-6) in 20- and 22-carbon highly unsaturated fatty acids with 3 or more double bonds (HUFA) accumulated in tissue HUFA (e.g., the %n-6 in HUFA) are biomarkers reflecting intakes of n-6 and n-3 fatty acids. An empirical equation, referred to here as the Lands' Equation, was developed previously to use dietary intakes of n-6 and n-3 HUFA and their 18-carbon precursors to estimate the %n-6 in HUFA of humans. From the PubMed database, we identified clinical trials reporting (a) dietary intake of at least linoleic acid (18:2n-6) and alpha-linolenic acid (18:3n-3), and (b) the amounts of at least arachidonic acid (20:4n-6), eicosapentaenoic acid (20:5n-3), and docosahexaenoic acid (22:6n-3) in lipids of plasma, serum, or red blood cell. Linear regression analyses comparing reported and predicted %n-6 in HUFA gave a correlation coefficient of 0.73 (p<0.000000) for 34 studies with 92 subject groups. These results indicate that circulating HUFA compositions can be reliably estimated from dietary intake data that not only includes n-3 and n-6 HUFA consumption, but also includes consumption of 18 carbon n-3 and n-6 precursor fatty acids.

Best practices for the design, laboratory analysis, and reporting of trials involving fatty acids

Fatty acids are among the most studied nutrients in human metabolism and health. Endogenous fatty acid status influences health and disease via multiple mechanisms at all stages of the life cycle. Despite widespread interest, attempts to summarize the results of multiple studies addressing similar fatty acid-related outcomes via meta-analyses and systematic reviews have been disappointing, largely because of heterogeneity in study design, sampling, and laboratory and data analyses. Our purpose is to recommend best practices for fatty acid clinical nutrition and medical studies. Key issues in study design include judicious choice of sampled endogenous pools for fatty acid analysis, considering relevant physiologic state, duration of intervention and/or observation, consideration of specific fatty acid dynamics to link intake and endogenous concentrations, and interpretation of results with respect to known fatty acid ranges. Key laboratory considerations include proper sample storage, use of sample preparation methods known to be fit-for-purpose via published validation studies, detailed reporting or methods to establish proper fatty acid identification, and quantitative analysis, including calibration of differential response, quality control procedures, and reporting of data on a minimal set of fatty acids to enable comprehensive interpretation. We present a checklist of recommendations for fatty acid best practices to facilitate design, review, and evaluation of studies with the intention of improving study reproducibility.

Highly unsaturated fatty acids (HUFA) mediate and monitor food's impact on health

A hyperbolic, saturable, competitive dynamic of ligand binding to metabolic enzymes and lipid mediator receptors gives non-linear dose-response interactions that need careful management when planning or interpreting nutrient-based interventions. Relatively indiscriminate metabolism during accumulation of HUFA from n-3 and n-6 nutrients allows the amounts of n-3 and n-6 nutrients to determine the HUFA balance accumulated in tissue phospholipids. However, when HUFA-based eicosanoid actions are more intense with n-6 than n-3 mediators, they cause healthy physiology to shift toward pathophysiology. The proportion of n-6 in tissue HUFA directly relates to the severity of conditions caused by excessive n-6 actions. In the absence of n-3 nutrients, dietary linoleate (18:2n-6) has a very narrow therapeutic window below 1 percent of food energy, and it is widened by n-3 nutrients. The predictable quantitative dynamics of competing n-3 and n-6 nutrients allows design of successful preventive nutrition protocols that confirm and extend the epidemiologically observed benefits of n-3 nutrients.

Is there A Role for Alpha-Linolenic Acid in the Fetal Programming of Health?

The role of ω3 alpha linolenic acid (ALA) in the maternal diet during pregnancy and lactation, and its effect on the prevention of disease and programming of health in offspring, is largely unknown. Compared to ALA, ω3 docosahexaenoic (DHA) and eicosapentaenoic (EPA) acids have been more widely researched due to their direct implication in fetal neural development. In this literature search we found that ALA, the essential ω3 fatty acid and metabolic precursor of DHA and EPA has been, paradoxically, almost unexplored. In light of new and evolving findings, this review proposes that ALA may have an intrinsic role, beyond the role as metabolic parent of DHA and EPA, during fetal development as a regulator of gene programming for the prevention of metabolic disease and promotion of health in offspring.

Kinetics of omega-3 polyunsaturated fatty acids when co-administered with saturated or omega-6 fats

OBJECTIVE

Absorption of long chain omega-3 polyunsaturated fatty acids (LCn-3PUFA) has been shown to be potentiated when consumed with a high fat meal. However, the effect of different dietary fats on n-3PUFA absorption and postprandial kinetics has not been previously studied.

METHOD

In a randomized cross-over design intervention, postprandial incorporation of LCn-3PUFA into plasma lipids following consumption of a meal rich in either saturated fat or omega-6 polyunsaturated fatty acids (n-6PUFA) was investigated. Healthy adult male and female subjects (n=26) were fed an isocaloric meal containing equivalent amount of either butter or sunflower seed oil supplemented with 1.8grams of LCn-3PUFA (300mg eicosapentaenoic acid, 20:5n-3 and 1500mg docosahexaenoic acid, 22:6n-3).

RESULTS

Postprandial plasma lipids were enriched with saturated fatty acids and linoleic acid (18:2n-6) following consumption of the butter and the sunflower oil containing meals respectively. The increase in plasma 20:5n-3 and 22:6n-3 levels over the 6hour study period was similar in both the saturated and the n-6 fat groups.

CONCLUSION

These results suggest that the expected competition between LCn-3PUFA and n-6PUFA at the absorption level is unlikely; therefore competition at the enzymatic level should be primarily responsible for differences in their metabolic and clinical effects. Trial registered with the Australia New Zealand Trial registry as ACTRN12612000654853.

Omega-3 PUFAs Lower the Propensity for Arachidonic Acid Cascade Overreactions

A productive view of the benefits from omega-3 (n-3) nutrients is that the dietary essential omega-6 (n-6) linoleic acid has a very narrow therapeutic window which is widened by n-3 nutrients. The benefit from moderate physiological actions of the arachidonic acid cascade can easily shift to harm from excessive pathophysiological actions. Recognizing the factors that predispose the cascade to an unwanted overactivity gives a rational approach for arranging beneficial interactions between the n-3 and n-6 essential nutrients that are initial components of the cascade. Much detailed evidence for harmful cascade actions was collected by pharmaceutical companies as they developed drugs to decrease those actions. A remaining challenge is to understand the factors that predispose the cascade toward unwanted outcomes and create the need for therapeutic interventions. Such understanding involves recognizing the similar dynamics for dietary n-3 and n-6 nutrients in forming the immediate precursors of the cascade plus the more vigorous actions of the n-6 precursor, arachidonic acid, in forming potent mediators that amplify unwanted cascade outcomes. Tools have been developed to aid deliberate day-to-day quantitative management of the propensity for cascade overactivity in ways that can decrease the need for drug treatments.

Balancing proportions of competing omega-3 and omega-6 highly unsaturated fatty acids (HUFA) in tissue lipids

People eating different balances of omega-3 and omega-6 nutrients develop predictably different proportions of competing highly unsaturated fatty acids (HUFA) in their tissue lipids. While epidemiological studies have associated wide differences in HUFA balance with disease severity, some clinical studies that did not examine wide differences failed to confirm the association. We examined the degree to which the relative amount of arachidonic acid, the major precursor of omega-6 eicosanoids, differs among people who have widely different dietary intakes of omega-3 and omega-6 nutrients. Gas chromatographic analyses of human blood samples describe the balance among n-3 and n-6 HUFA for different individuals. The proportion of the omega-6 arachidonic acid, from which potent eicosanoids are formed, is not constant. It ranges from 30% to 70% of HUFA while the competing n-3 HUFA range from 60% to 10% of HUFA. Significant differences in clinical outcomes between control and intervention groups have been seen when using dietary interventions that shift the balance of n-3 and n-6 nutrients far enough to create a biologically significant difference in the HUFA balance.

Historical perspectives on the impact of n-3 and n-6 nutrients on health

Current public advice from the Food and Nutrition Board (FNB) about essential fatty acids (EFA) has limited quantitative details about three processes: (1) similar dynamics for n-3 linolenic and n-6 linoleic polyunsaturated fatty acids (PUFA) in maintaining 20- and 22-carbon n-3 and n-6 highly unsaturated fatty acids (HUFA) in tissues; (2) different dynamics for tissue n-3 and n-6 HUFA during formation and action of hormone-like eicosanoids; (3) simultaneous formation of non-esterified fatty acids (NEFA) and low density lipoprotein (LDL) from very low density lipoprotein (VLDL) formed from excess food energy and secreted by the liver. This report reviews evidence that public health may benefit from advice to eat less n-6 nutrients, more n-3 nutrients and fewer calories per meal. Explicit data for linoleic acid fit an Estimated Average Requirement (EAR) near 0.1 percent of daily food energy (en%) meeting needs of half the individuals in a group, a Recommended Dietary Allowance (RDA) near 0.5 en% meeting needs of 97-98 percent of individuals, and a Tolerable Upper Intake Level (UL) near 2 en% having no likely risk of adverse health effects. Quantitative tools help design and monitor explicit interventions that could beneficially replace imprecise advice on "healthy foods" with explicit preventive nutrition.

Dietary linoleic acid elevates the endocannabinoids 2-AG and anandamide and promotes weight gain in mice fed a low fat diet

Dietary intake of linoleic acid (LNA, 18:2n-6) has increased dramatically during the 20th century and is associated with greater prevalence of obesity. The endocannabinoid system is involved in regulation of energy balance and a sustained hyperactivity of the endocannabinoid system may contribute to obesity. Arachidonic acid (ARA, 20:4n-6) is the precursor for 2-AG and anandamide (AEA), and we sought to determine if low fat diets (LFD) could be made obesogenic by increasing the endocannabinoid precursor pool of ARA, causing excessive endocannabinoid signaling leading to weight gain and a metabolic profile associated with obesity. Mice (C57BL/6j, 6 weeks of age) were fed 1 en% LNA and 8 en% LNA in low fat (12.5 en%) and medium fat diets (MFD, 35 en%) for 16 weeks. We found that increasing dietary LNA from 1 to 8 en% in LFD and MFD significantly increased ARA in phospholipids (ARA–PL), elevated 2-AG and AEA in liver, elevated plasma leptin, and resulted in larger adipocytes and more macrophage infiltration in adipose tissue. In LFD, dietary LNA of 8 en% increased feed efficiency and caused greater weight gain than in an isocaloric reduction to 1 en% LNA. Increasing dietary LNA from 1 to 8 en% elevates liver endocannabinoid levels and increases the risk of developing obesity. Thus a high dietary content of LNA (8 en%) increases the adipogenic properties of a low fat diet.

Maternal milk DHA content predicts cognitive performance in a sample of 28 nations

Convergent evidence from neuronal biology and hominin brain hypertrophy suggests that omega-3 fatty acids are a limiting resource for neural and cognitive development in Homo sapiens, and therefore that children from populations with higher omega-3 availability should display superior cognitive performance. Using multiple regression, we tested this prediction in a sample of 28 countries, with Programme for International Student Assessment (PISA) math scores in 2009 as an index of cognitive performance, and country-specific breast milk levels of omega-3 docosahexaenoic acid (DHA) as an index of omega-3 availability. Breast milk DHA makes a highly significant contribution to math scores (β = 0.462, P = 0.006), greater in magnitude than the control variables of per capita Gross Domestic Product (PCGDP) and educational expenditures per pupil. Together, dietary fish (positively) and total fat (negatively) explain 61% of the variance in maternal milk DHA in a larger sample of 39 countries.

Interactions of linoleic and alpha-linolenic acids in the development of fatty acid alterations in cystic fibrosis

Patients with cystic fibrosis (CF) exhibit characteristic polyunsaturated fatty acid abnormalities, including low linoleic acid and high arachidonic acid levels that are thought to contribute to the pathophysiology of this disease. Recent studies indicate that changes in fatty acid metabolism are responsible for these abnormalities. This study examines the role of fatty acid substrate concentrations in the development of these alterations in a cultured cell model of CF. By incubating cells with varying concentrations of exogenous fatty acids, it shows that increasing the concentration of substrates from the parallel n-3 and n-6 polyunsaturated fatty acid pathways (linoleic acid and alpha-linolenic acid, respectively) not only increases formation of the products in that pathway, but also reduces metabolism in the parallel pathway. In particular, we demonstrate that high levels of linoleic acid and low levels of alpha-linolenic acid are required to observe the typical fatty acid alterations of cystic fibrosis. These results shed light on the mechanisms of fatty acid metabolic abnormalities in cystic fibrosis. They also have implications for the nutritional therapy of CF, highlighting the importance of specific fatty acid content, and in understanding the anti-inflammatory effects of n-3 fatty acids.

Δ-6 Desaturase substrate competition: dietary linoleic acid (18:2n-6) has only trivial effects on α-linolenic acid (18:3n-3) bioconversion in the teleost rainbow trout

It is generally accepted that, in vertebrates, omega-3 (n-3) and omega-6 (n-6) poly-unsaturated fatty acids (PUFA) compete for Δ-6 desaturase enzyme in order to be bioconverted into long-chain PUFA (LC-PUFA). However, recent studies into teleost fatty acid metabolism suggest that these metabolic processes may not conform entirely to what has been previously observed in mammals and other animal models. Recent work on rainbow trout has led us to question specifically if linoleic acid (LA, 18∶2n-6) and α-linolenic acid (ALA, 18∶3n-3) (Δ-6 desaturase substrates) are in direct competition for access to Δ-6 desaturase. Two experimental diets were formulated with fixed levels of ALA, while LA levels were varied (high and low) to examine if increased availability of LA would result in decreased bioconversion of ALA to its LC-PUFA products through substrate competition. No significant difference in ALA metabolism towards n-3 LC-PUFA was exhibited between diets while significant differences were observed in LA metabolism towards n-6 LC-PUFA. These results are evidence for minor if any competition between substrates for Δ-6 desaturase, suggesting that, paradoxically, the activity of Δ-6 desaturase on n-3 and n-6 substrates is independent. These results call for a paradigm shift in the way we approach teleost fatty acid metabolism. The findings are also important with regard to diet formulation in the aquaculture industry as they indicate that there should be no concern for possible substrate competition between 18∶3n-3 and 18∶2n-6, when aiming at increased n-3 LC-PUFA bioconversion in vivo.

Selective sensitization of tumors to chemotherapy by marine-derived lipids: a review

Despite great improvements, a significant proportion of cancer patients still die, mainly because of the development of metastases. At this stage, current treatments still rely heavily on conventional chemotherapy for most cancers. The efficacy of chemotherapy is dose-dependent, which is limited by toxicity to non-tumor tissues, as a result of its poor tumor selectivity. To improve survival length and preserve quality of life, the challenge is to develop approaches aimed at increasing chemotherapy toxicity to tumor tissue while not affecting non-tumor tissues. Marine-derived lipids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), have the potential to differentially sensitize tissues to chemotherapy. These lipids enhance the cytotoxicity of 15 anticancer drugs (antimetabolites, alkylating or intercalating agents, microtubule stabilizers, Abl tyrosine kinase inhibitor and arsenic trioxide) to a variety of cancer cell lines or tumors in animals, used as models for breast, prostate, colonic, lung, cervical, ovarian cancers, neuroblastomas, leukemia or lymphomas. However, DHA and EPA do not sensitize non-tumor tissues to anticancer drugs, which suggests that the effect of these lipids is tumor selective. Two phase II clinical trials already support these results, and randomized, phase III trials are ongoing. In this review, we discuss the double-faceted properties of these lipids, and then focus on their potential for transfer to the patient in the light of current therapeutic strategies. Should their beneficial effects be confirmed, the consequences could be considerable by opening up the prospect of systematic supplementation during cancer treatment, a significant shift in current cancer therapeutic paradigms.

EPA and DHA--protein, not fat is "where it's at"?

Guidelines and recommendations for the dietary intake of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are topics of debate. Recently, EPA and DHA intakes have been demonstrated to be associated with dietary protein intakes and not dietary fat intakes that are distinct from α-linolenic acid. We presently confirm these observations in a secondary analysis of baseline dietary intake data for the validation of a food frequency questionnaire (n=99). DHA intakes measured by both 3 d dietary record and food frequency questionnaire and EPA intakes measured by food frequency questionnaire were positively correlated with protein intakes. EPA and DHA were not associated with fat intakes in either assessment, while ?-linolenic acid was positively correlated with fat intakes. Future recommendations regarding the intake of omega-3 polyunsaturated fatty acids, and EPA and DHA specifically, should consider these associations that provide insight on dietary sources of EPA and DHA in the food supply.

Using 3-6 differences in essential fatty acids rather than 3/6 ratios gives useful food balance scores

BACKGROUND

The vitamin-like omega-3 and omega-6 essential fatty acids are converted in the body to a large family of hormones which act at selective receptors that occur on nearly every cell and tissue. A relative omega-3 deficit allows overabundant actions of omega-6 hormones to develop into health disorders. People need simple, explicit information on the balance of essential fatty acids in their foods to avoid accumulating unintended imbalances in their tissue omega-3 and omega-6 fatty acids.

RESULTS

We developed an Omega 3-6 Balance Food Score that summarizes in a single value the balance among eleven omega-3 and omega-6 essential fatty acids in a food. The value allows a quantitative estimate of the impact of each food item on the proportions of omega-3 and omega-6 that will accumulate in the 20- and 22-carbon highly unsaturated fatty acids of blood, which is an important health risk assessment biomarker.

CONCLUSIONS

The impact of an individual food item upon a useful health risk assessment biomarker is easily evident in a simple, explicit value for the balance among eleven essential fatty acids nutrients. Foods with more positive Omega 3-6 Balance Food Scores will increase the percent of omega-3 in the biomarker, whereas those with more negative Scores will increase the percent of omega-6 in the biomarker.

Gestational age dependent changes of the fetal brain, liver and adipose tissue fatty acid compositions in a population with high fish intakes

INTRODUCTION

There are no data on the intrauterine fatty acid (FA) compositions of brain, liver and adipose tissue of infants born to women with high fish intakes.

SUBJECTS AND METHODS

We analyzed the brain (n=18), liver (n=14) and adipose tissue (n=11) FA compositions of 20 stillborn infants with different gestational ages (range 8-38 weeks) born to Tanzanian women with low linoleic acid (LA) intakes and high intakes of docosahexaenoic (DHA) and arachidonic (AA) acids from local fish.

RESULTS AND DISCUSSION

With advancing gestation, brain saturated-FA (SAFA; in g/100g FA), polyunsaturated-FA (PUFA), DHA, 20:3ω6, 22:4ω6 and 22:5ω6 increased, while monounsaturated-FA (MUFA), 20:3ω9, 22:3ω9 and AA decreased. Decreasing brain AA might be caused by increasing AA-metabolism to 20:3ω6, 22:4ω6 and 22:5ω6. In the liver, SAFA, PUFA and LA increased, while MUFA decreased with gestation. The steep increase of (mostly de novo synthesized) SAFA in adipose tissue coincided with relative decreases of MUFA, PUFA, DHA, LA and AA with advancing gestation. Compared to Western infants, the currently studied African infants had higher DHA, lower AA, and a higher DHA/AA-ratio in brain and adipose tissue, while the LA content of adipose tissue was lower.

CONCLUSION

The low LA and high DHA and AA intakes by the mothers of these infants might support optimal α-linolenic (ALA) vs. LA competition for Δ5D and Δ6D-activities and DHA vs. AA antagonism. Conversely, the Western diet, characterized by high LA and lower DHA and AA intakes, might disturb these evolutionary conserved mechanisms aiming at an optimal ω3/ω6-balance.

α-Linolenate reduces the dietary requirement for linoleate in the growing rat

BACKGROUND

We hypothesized that due to the absence of a dietary source of omega-3 fatty acids, the essential fatty acid (EFA) deficiency model leads to an overestimate of linoleic acid (LA) requirements.

METHODS

over 7wk, young rats consumed an EFA diet containing either 0en% linoleate (0LA) and 0en% α-linolenate (0LNA) or a diet containing 0.5en% LNA plus one of seven levels of added LA (0.12-4.0en%; n=6/group).

RESULTS

Rats consuming the 0LA-0LNA diet had the lowest final body weight, 34-68% lower LA and arachidonate in plasma and liver, 87% lower LA in epididymal fat, and an 8-20 fold higher eicosatrienoate in plasma, liver and muscle lipids. 0.5LNA completely prevented the lower growth and partly prevented the rise in eicosatrienoate seen in the 0LA-0LNA group.

CONCLUSION

Providing dietary LNA at 0.5 en% reduces the rat's physiological requirement for LA by an estimated factor of at least four (0.5en% instead of 2en%). Since LA requirements in humans are also based on the same flawed model of EFA deficiency, it is plausible that they too have been overestimated and should therefore be reinvestigated.

Omega-3 fatty acids and metabolic syndrome: effects and emerging mechanisms of action

Epidemiological, human, animal, and cell culture studies show that n-3 fatty acids, especially α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), reduce the risk factors of cardiovascular diseases. EPA and DHA, rather than ALA, have been the focus of research on the n-3 fatty acids, probably due to the relatively inefficient conversion of ALA to EPA and DHA in rodents and humans. This review will assess our current understanding of the effects and potential mechanisms of actions of individual n-3 fatty acids on multiple risk factors of metabolic syndrome. Evidence for pharmacological responses and the mechanism of action of each of the n-3 fatty acid trio will be discussed for the major risk factors of metabolic syndrome, especially adiposity, dyslipidemia, insulin resistance and diabetes, hypertension, oxidative stress, and inflammation. Metabolism of n-3 and n-6 fatty acids as well as the interactions of n-3 fatty acids with nutrients, gene expression, and disease states will be addressed to provide a rationale for the use of n-3 fatty acids to reduce the risk factors of metabolic syndrome.

Allometric scaling of dietary linoleic acid on changes in tissue arachidonic acid using human equivalent diets in mice

Background

It is hypothesized that dietary linoleic acid (LA) promotes chronic and acute diseases in humans by enriching tissues with arachidonic acid (AA), its downstream metabolite, and dietary studies with rodents have been useful for validation. However, levels of LA in research diets of rodents, as published in the literature, are notoriously erratic making interspecies comparisons unreliable. Therefore, the ability to extrapolate the biological effects of dietary LA from experimental rodents to humans necessitates an allometric scaling model that is rooted within a human equivalent context.

Methods

To determine the physiological response of dietary LA on tissue AA, a mathematical model for extrapolating nutrients based on energy was used, as opposed to differences in body weight. C57BL/6J mice were divided into 9 groups fed a background diet equivalent to that of the US diet (% energy) with supplemental doses of LA or AA. Changes in the phospholipid fatty acid compositions were monitored in plasma and erythrocytes and compared to data from humans supplemented with equivalent doses of LA or AA.

Results

Increasing dietary LA had little effect on tissue AA, while supplementing diets with AA significantly increased tissue AA levels, importantly recapitulating results from human trials.

Conclusions

Thus, interspecies comparisons for dietary LA between rodents and humans can be achieved when rodents are provided human equivalent doses based on differences in metabolic activity as defined by energy consumption.

Animal studies of the functional consequences of suboptimal polyunsaturated fatty acid status during pregnancy, lactation and early post-natal life

Scores of animal studies demonstrate that seed oils replete with linoleic acid and very low in linolenic acid fed as the exclusive source of fat through pregnancy and lactation result in visual, cognitive, and behavioural deficits in the offspring. Commodity peanut, sunflower, and safflower oils fed to mother rats, guinea pigs, rhesus monkeys, and baboons induce predictable changes in tissue polyunsaturated fatty acid composition that are abnormal in free-living land mammals as well as changes in neurotransmitter levels, catecholamines, and signalling compounds compared with animals with a supply of ω3 polyunsaturated fatty acid. These diets consistently induce functional deficits in electroretinograms, reflex responses, reward or avoidance induced learning, maze learning, behaviour, and motor development compared with ω3 replete groups. Boosting neural tissue docosahexaenoic acid (DHA) by feeding preformed DHA enhances visual and cognitive function. Though no human randomized controlled trials on minimal ω3 requirements in pregnancy and lactation have been conducted, the weight of animal evidence compellingly shows that randomizing pregnant or lactating humans to diets that include high linoleate oils as the sole source of fat would be frankly unethical because they would result in suboptimal child development. Increasing use of commodity ω3-deficient oils in developing countries, many in the name of heart health, will limit brain development of the next generation and can be easily corrected at minimal expense by substituting high oleic acid versions of these same oils, in many cases blended with small amounts of α-linolenic acid oils like flax or perilla oil. Inclusion of DHA in these diets is likely to further enhance visual and neural development.

Elevated plasma fibrinogen caused by inadequate alpha-linolenic acid intake can be reduced by replacing fat with canola-type rapeseed oil

The effects of canola-type rapeseed oil (RSO) on serum lipids, plasma fibrinogen, lipid oxidation and fatty acids were studied in three groups of subjects, two of which had not been consuming fish in their habitual diets. Forty-two volunteers (35 women, 7 men, 16-62 years) replaced fat with RSO for 6 weeks in a parallel design. The average cholesterol and fibrinogen concentrations were 5.0 mmol/l and 2.6 g/l, respectively. The intake of alpha-linolenic acid (alpha-LLA) was doubled. Efficient competitive inhibition by alpha-LLA was seen as a decrease in long-chain (LC) n-6 PUFA at 3 weeks. Elevated fibrinogen (2.6-3.9 g/l) decreased by 0.95 g/l at 6 weeks. Docosahexaenoic acid (22:6n-3) in plasma phospholipids increased at low fibrinogen levels only. The associations and changes in plasma C18 and LC PUFA followed the competitive and metabolic principles of the body, and especially in the case of n-3 PUFA according to the recycling pathway.

Low dietary fish-oil threshold for myocardial membrane n-3 PUFA enrichment independent of n-6 PUFA intake in rats

Long chain n-3 PUFA docosahexaenoic acid (DHA) is important for heart and brain function. Investigations of biologically plausible mechanisms using animal models associate cardioprotection with DHA incorporation into myocardial membranes that are largely derived from supra-physiological fish oil (FO) intake. We measured the incorporation of DHA into myocardial membranes of rats from low dietary FO intake within human dietary range and quantitatively assessed the influence of dietary n-6 PUFA. With rats fed diets containing 0.16%-5% FO, equal to 0.12%-8.7% energy (%en) as eicosapentaenoic acid (EPA) and DHA (EPA+DHA), and either 1.5%en or 7.5%en n-6 PUFA (linoleic acid) for four weeks, dietary n-6:n-3 PUFA ratios ranged from 74 to 0.3. Myocardial DHA concentration increased in a log-linear fashion with a dietary threshold of 0.019%en as EPA+DHA and half maximal dietary [EPA+DHA] equal to 0.29%en (95% CI, 0.23-0.35). Dietary linoleic acid intake did not influence myocardial DHA. Myocardial membranes are sensitive to absolute dietary intake of long chain n-3 PUFA at low %en in the rat, equivalent to a human intake of one meal of fatty fish per week or less. The dietary ratio of n-6:n-3 PUFA has no influence on long chain n-3 PUFA cellular incorporation from dietary fish oil.

Membrane fatty acid composition of rat skeletal muscle is most responsive to the balance of dietary n-3 and n-6 PUFA

The present study quantifies the relationships between diet fatty acid profile and fatty acid composition of rat skeletal muscle phospholipids. Young adult male Sprague–Dawley rats were fed, for 8 weeks, on one of twelve moderate-fat diets (25 % of total energy) differing only in fatty acid profile. SFA content ranged from 8–88 % of total fatty acids, MUFA 6–65 %, total PUFA 4–81 %, n-6 PUFA 3–70 % and n-3 PUFA 1–70 %. Diet PUFA included only essential fatty acids 18 : 2n-6 and 18 : 3n-3. The balance between n-3 and n-6 PUFA (PUFA balance) in the diet ranged from 1 : 99 to 86 : 14 % n-3 PUFA:n-6 PUFA. The slope of muscle phospholipid composition plotted against diet composition quantifies the response of muscle membrane composition to dietary fat (0, no response; 1, complete conformity with diet). The resulting slopes were 0·02 (SFA), 0·10 (PUFA), 0·11 (MUFA), 0·14 (n-3 PUFA) and 0·23 (n-6 PUFA). The response to PUFA balance was biphasic with a slope of 0·98 below 10 % diet PUFA balance and 0·16 above 10 %. Thus, low diet PUFA balance has greater influence on muscle composition than 18-carbon n-3 or n-6 PUFA individually. Equations provided may allow prediction of muscle composition for other diet studies. Diet PUFA balance dramatically affects muscle 20 : 4n-6 and 22 : 6n-3. This may have significant implications for some disease states in human subjects.

Novel fatty acid desaturase 3 (FADS3) transcripts generated by alternative splicing

Fatty acid desaturase 1 and 2 (FADS1 and FADS2) code for the key desaturase enzymes involved in the biosynthesis of long chain polyunsaturated fatty acids in mammals. FADS3 shares close sequence homology to FADS1 and FADS2 but the function of its gene product remains unknown. Alternative transcripts (AT) generated by alternative splicing (AS) are increasingly recognized as an important mechanism enabling a single gene to code for multiple gene products. We report the first AT of a FADS gene, FADS3, generated by AS. Aided by ORF Finder, we identified putative coding regions of eight AT for FADS3 with 1.34 kb (classical splicing), 1.14 (AT1), 0.77 (AT2), 1.25 (AT3), 0.51 (AT4), 0.74 (AT6), and 1.11 (AT7). In addition we identified a 0.51 kb length transcript (AT5) that has a termination codon within intron 8-9. The expression of each AT was analyzed in baboon neonate tissues and in differentiated and undifferentiated human SK-N-SH neuroblastoma cells. FADS3 AT are expressed in 12 neonate baboon tissues and showed reciprocal increases and decreases in expression changes in response to human neuronal cell differentiation. FADS3 AT, conserved in primates and under metabolic control in human cells, are a putative mediator of LCPUFA biosynthesis and/or regulation.

Recent trends in the advanced analysis of bioactive fatty acids

The consumption of dietary fats have been long associated to chronic diseases such as obesity, diabetes, cancer, arthritis, asthma, and cardiovascular disease; although some controversy still exists in the role of dietary fats in human health, certain fats have demonstrated their positive effect in the modulation of abnormal fatty acid and eicosanoid metabolism, both of them associated to chronic diseases. Among the different fats, some fatty acids can be used as functional ingredients such as alpha-linolenic acid (ALA), arachidonic acid (AA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), gamma-linolenic acid (GLA), stearidonic acid (STA) and conjugated linoleic acid (CLA), among others. The present review is focused on recent developments in FAs analysis, covering sample preparation methods such as extraction, fractionation and derivatization as well as new advances in chromatographic methods such as GC and HPLC. Special attention is paid to trans fatty acids due its increasing interest for the food industry.

Dietary linoleic acid has no effect on arachidonic acid, but increases n-6 eicosadienoic acid, and lowers dihomo-gamma-linolenic and eicosapentaenoic acid in plasma of adult men

High intakes of linoleic acid (LA,18:2n-6) have raised concern due to possible increase in arachidonic acid (ARA, 20:4n-6) synthesis, and inhibition of alpha linolenic acid (ALA, 18:3n-3) desaturation to eicosapentaenoic (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3). In healthy men, 10.5% energy compared to 3.8% energy LA with 1% energy ALA increased plasma phospholipid LA and 20:2n-6, the elongation product of LA, and decreased EPA, with no change in ARA. However, LA was inversely related to ARA at both 10.5% energy and 3.8% energy LA, (r=-0.761, r=-0.817, p<0.001, respectively). A two-fold variability in ARA among individuals was not explained by the dietary LA, ARA, ALA, or fish intake. Our results confirm LA requirements for ARA synthesis is low, <3.8% energy, and they suggest current LA intakes saturate Delta-6 desaturation and adversely affect n-3 fatty acid metabolism. Factors other than n-6 fatty acid intake are important modifiers of plasma ARA.

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

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

High dietary omega-6 fatty acids contribute to reduced docosahexaenoic acid in the developing brain and inhibit secondary neurite growth

Docosahexaenoic acid (DHA, 22:6omega-3) is a major polyunsaturated fatty acid in the brain and is required in large amounts during development. Low levels of DHA in the brain are associated with functional deficits. The omega-3 fatty acids are essential nutrients and their metabolism and incorporation in developing brain depends on the composition of dietary fat. We assessed the importance of the intake of the omega-3 fatty acid, 18:3omega-3 and the balance with the omega-6 fatty acid, 18:2omega-6, and the effects of dietary arachidonic acid (20:4omega-6) and DHA in milk diets using the piglet as a model of early infant nutrition. Piglets were fed (% energy) 1.2% 18:2omega-6 and 0.05% 18:3omega-3 (deficient), 10.7% 18:2omega-6 and 1.1% 18:3omega-3 (contemporary), 1.2% 18:2omega-6 and 1.1% 18:3omega-3 (evolutionary), or the contemporary diet with 0.3% 20:4omega-6 and 0.3% DHA (supplemented) from birth to 30 days of age. Our results show that a contemporary diet, high in 18:2omega-6 compromises DHA accretion and leads to increased 22:4omega-6 and 22:5omega-6 in the brain. However, an evolutionary diet, low in 18:2omega-6, supports high brain DHA. DHA supplementation effectively increased DHA, but not the intermediate omega-3 fatty acids, 20:5omega-3 and 22:5omega-3. Using primary cultures of cortical neurons, we show that 22:5omega-6 is efficiently acylated and preferentially taken up over DHA. However, DHA, but not 22:5omega-6 supports growth of secondary neurites. Our results suggest the need to consider whether current high dietary omega-6 fatty acid intakes compromise brain DHA accretion and contribute to poor neurodevelopment.

An emerging risk factor for obesity: does disequilibrium of polyunsaturated fatty acid metabolism contribute to excessive adipose tissue development?

A positive energy balance (energy intake>energy expenditure), in which total fat intake plays an important role, is commonly regarded as a major factor contributing to obesity. Adipose tissue development, i.e. both size (hypertrophy) and number (hyperplasia), is stimulated by high dietary fat intake during early postnatal development, a susceptibility that now appears to continue well into adulthood. Recent human and animal studies suggest that by altering rates of adipocyte differentiation and proliferation, differences in the composition of dietary fat may also contribute to adipose tissue development. At least in rodent models, the relative intake of n-6 to n-3 PUFA is clearly emerging as a new factor in this development. In these models, higher linoleate intake raises tissue arachidonic acid, which increases prostacyclin production and, in turn, stimulates signalling pathways implicated in adipogenesis. Signalling pathways stimulated by arachidonic acid probably include phospholipase and/or cyclo-oxygenase activation and may be linked as much to relatively low intake of n-3 PUFA as to excessive dietary linoleate. One factor potentially contributing to oversight about the apparent role of dietary n-6 PUFA (especially excess dietary linoleate) in adipose tissue development is the historical overestimation of linoleate requirements and the enthusiasm for higher intake of 'essential fatty acids'. More research is needed to address whether disequilibration of dietary PUFA intake contributes to the risk of obesity in humans.

A critique of paradoxes in current advice on dietary lipids

Beliefs about credible hypotheses of dietary causes of disease still need well-defined mediators to test for logical proof or disproof. We know that food energy causes transient postprandial oxidative insults that may not be fully reversible. Also, eating vitamin-like 18-carbon polyunsaturated fatty acids (PUFA) in foods maintains the 20- and 22-carbon highly unsaturated fatty acids (HUFA) in tissues. Tissue HUFA form hormone-like mediators that each amplify transient postprandial insults into fatal inflammatory, thrombotic and arrhythmic events in cardiovascular disease, a major preventable cause of death. Similar diet-based amplified events may also occur in other inflammatory proliferative disorders including cancer, dementia, arthritis and asthma. Puzzling paradoxes come from fragmented views of this situation which convey incomplete knowledge in oversimplified messages. Tools now exist to demonstrate successful prevention of two fatal food imbalances with credible dietary preventive interventions, but organizers and financers to help gather the evidence remain unknown. The overall evidence accumulated about diet, disease and death may be nearing a paradigm shift in which prior observed facts remain while beliefs about their accepted interpretation change.

Artificial rearing with docosahexaenoic acid and n-6 docosapentaenoic acid alters rat tissue fatty acid composition

Docosahexaenoic acid (DHA; 22:6n-3) and n-6 docosapentaenoic acid (DPAn-6; 22:5n-6) are components of enriched animal feed and oil derived from Schizochytrium species microalgae. A one generation, artificial rearing model from day 2 after birth onward (AR) and a dam-reared control group (DAM) were used to examine DPAn-6 feeding on the fatty acid composition of various rat tissues at 15 weeks of age. Four AR diets were based on an n-3 fatty acid-deficient, 18:2n-6-based artificial milk with 22:6n-3 and/or 22:5n-6 added: AR-LA, AR-DHA, AR-DPAn-6, and AR-DHA+DPAn-6. The 22:6n-3 levels for the DAM, AR-DHA, and AR-DHA+DPAn-6 groups tended to be similar and higher than in the AR-LA and AR-DPAn-6 groups. The levels of 22:5n-6 tended to be higher only in the absence of dietary 22:6n-3. Adipose levels of 22:5n-6 was the only exception, as 22:5n-6 was significantly higher in AR-DHA+DPAn-6 than was observed in either the DAM or the AR-DHA group. There were no differences in 20:4n-6 levels within the tissues examined. In conclusion, 22:5n-6 replaces 22:6n-3 in the absence of 22:6n-3 only and does not appear to compete with 22:6n-3 in the presence of dietary 22:6n-3, suggesting that oils containing 22:5n-6 and 22:6n-3 may be a good dietary source of 22:6n-3.

Healthy intakes of n-3 and n-6 fatty acids: estimations considering worldwide diversity

BACKGROUND

The worldwide diversity of dietary intakes of n-6 and n-3 fatty acids influences tissue compositions of n-3 long-chain fatty acids (LCFAs: eicosapentaenoic, docosapentaenoic, and docosahexaenoic acids) and risks of cardiovascular and mental illnesses.

OBJECTIVE

We aimed to estimate healthy dietary allowances for n-3 LCFAs that would meet the nutrient requirements of 97-98% of the population.

DESIGN

Deficiency in n-3 LCFAs was defined as attributable risk from 13 morbidity and mortality outcomes, including all causes, coronary heart disease, stroke, cardiovascular disease, homicide, bipolar disorder, and major and postpartum depressions. Dietary availability of n-3 LCFAs from commodities for 38 countries and tissue composition data were correlated by best fit to each illness in deficiency risk models.

RESULTS

The potential attributable burden of disease ranged from 20.8% (all-cause mortality in men) to 99.9% (bipolar disorder). n-3 LCFA intake for Japan (0.37% of energy, or 750 mg/d) met criteria for uniformly protecting >98% of the populations worldwide. n-3 LCFA intakes needed to meet a tissue target representative of Japan (60% n-3 in LCFA) ranged from 278 mg/d (Philippines, with intakes of 0.8% of energy as linoleate, 0.08% of energy as alpha-linolenate, and 0.06% of energy as arachidonic acid) to 3667 mg/d (United States, with 8.91% of energy as linoleate, 1.06% of energy as alpha-linolenate, and 0.08% of energy as arachidonic acid).

CONCLUSIONS

With caveats inherent for ecologic, nutrient disappearance analyses, a healthy dietary allowance for n-3 LCFAs for current US diets was estimated at 3.5 g/d for a 2000-kcal diet. This allowance for n-3 LCFAs can likely be reduced to one-tenth of that amount by consuming fewer n-6 fats.