[datBtrue]

Source: Phytochemicals: Nutrient-Gene Interactions,
Mark S. Meskin (Editor),
CRC; 1 edition (February 22, 2006)
pp 137-159

Evolutionary Aspects of Diet, the Omega-6/Omega-3 Ratio, and Gene Expression
Artemis P. Simopoulos

CONTENTS

• Introduction
• Evolutionary Aspects of Diet with Emphasis on Omega-6 and Omega-3 Essential Fatty Acids
• Biological Effects and Metabolic Functions of Omega-6 and Omega-3 Fatty Acids
• Clinical Intervention Studies and the Omega-6/Omega-3 EFA Balance
• Omega-3 Fatty Acids and Gene Expression
• Diet–Gene Interactions: Genetic Variation and Omega-6 and Omega-3
• Fatty Acid Intake in the Risk for Cardiovascular Disease
• Conclusions
• References

INTRODUCTION

The interaction of genetics and environment, nature and nurture, is the foundation for all health and disease. In the last two decades, using the techniques of molecular biology, it has been shown that genetic factors determine susceptibility to disease and environmental factors determine which genetically susceptible individuals will be affected.1–6 Nutrition is an environmental factor of major importance. Whereas major changes have taken place in our diet over the past 10,000 years since the beginning of the Agricultural Revolution, our genes have not changed. The spontaneous mutation rate for nuclear DNA is estimated at 0.5% per million years. Therefore, over the past 10,000 years there has been time for very little change in our genes, perhaps 0.005%. In fact, our genes today are very similar to the genes of our ancestors during the Paleolithic period 40,000 years ago, at which time our genetic profile was established.7 Genetically speaking, humans today live in a nutritional environment that differs from that for which our genetic constitution was selected. Studies on the evolutionary aspects of diet indicate that major changes have taken place in our diet, particularly in the type and amount of essential fatty acids and in the antioxidant content of foods 7–11 (Table 10.1; Figure 10.1). Using the tools of molecular biology and genetics, research is defining the mechanisms by which genes influence nutrient absorption, metabolism and excretion, taste perception, and degree of satiation — and the mechanisms by which nutrients influence gene expression.




EVOLUTIONARY ASPECTS OF DIET WITH EMPHASIS ON OMEGA-6 AND OMEGA-3 ESSENTIAL FATTY ACIDS

The foods that were commonly available to pre-agricultural humans (lean meat, fish, green leafy vegetables, fruits, nuts, berries, and honey) were the foods that shaped modern humans’ genetic nutritional requirements. Cereal grains as a staple food area relatively recent addition to the human diet and represent a dramatic departure from those foods to which we are genetically programmed and adapted.12–17 Cereals did not become a part of our food supply until very recently — 10,000 years ago — with the advent of the Agricultural Revolution. Prior to the Agricultural Revolution humans ate an enormous variety of wild plants, whereas today about 17% of plant species provide 90% of the world’s food supply, with the greatest percentage contributed by cereal grains.12 Three cereals: wheat, maize, and rice together account for 75% of the world’s grain production. Human beings have become entirely dependent upon cereal grains for the greater portion of their food supply. The nutritional implications of such a high grain consumption upon human health are enormous. Cereal grains are high in carbohydrates and omega-6 fatty acids, but low in omega-3 fatty acids and in antioxidants, particularly in comparison to green leafy vegetables. Recent studies show that low-fat, high-carbohydrate diets increase insulin resistance and hyperinsulinemia, conditions that increase the risk for coronary heart disease, hypertension, diabetes, and obesity.18–21 And yet, for the 99.9% of mankind’s presence on this planet, humans rarely or never consumed cereal grains. It is only since the last 10,000 years that humans have consumed cereals. Up to that time, humans were non-cereal-eating hunter-gatherers — since the emergence of Homoerectus 1.7 million years ago. There is no evolutionary precedent in our species for grass seed consumption.7,12 Therefore, we have had little time (<500 generations) — since the beginning of the Agricultural Revolution 10,000 years ago — to adapt to a food type that now represents humanity’s major source of both calories and protein. A number of anthropological, nutritional, and genetic studies indicate that humans’ overall diet, including energy intake and energy expenditure, has changed over the past 10,000 years with major changes occurring during the past 150 years in the type and amount of fat and vitamins C and E intake 7,9,13,22,23,26,27 (Table 10.1 and Table 10.2; Figure 10.1).

Eaton and Konner 7 have estimated higher intakes for protein, calcium, potassium, and ascorbic acid and lower sodium intakes for the diet of the late Paleolithic period than the current U.S. and Western diets. Most of our food is calorically concentrated in comparison with wild game and the uncultivated fruits and vegetables of the Paleolithic diet. Paleolithic man consumed fewer calories and drank water, whereas today most drinks to quench thirst contain calories. Today industrialized societies are characterized by (1) an increase in energy intake and decrease in energy expenditure; (2) an increase in saturated fat, omega-6 fatty acids, and trans fatty acids, and a decrease in omega-3 fatty acid intake; (3) a decrease in complex carbohydrates and fiber; (4) an increase in cereal grains and a decrease in fruits and vegetables; and (5) a decrease in protein, antioxidants, and calcium intake7,9,22,23,24,25,26 (Table 10.1–Table 10.3). The increase in trans fatty acids is detrimental to health as shown in Table 10.4.28 In addition, trans fatty acids interfere with the desaturation and elongation of both omega-6 and omega-3 fatty acids, further decreasing the amount of arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid availability for human metabolism.29




BIOLOGICAL EFFECTS AND METABOLIC FUNCTIONS OF OMEGA-6 AND OMEGA-3 FATTY ACIDS

Food technology and agribusiness provided the economic stimulus that dominated the changes in the food supply.30,31 From per capita quantities of foods available for consumption in the U.S. national food supply in 1985, the amount of eicosapentaenoic acid (EPA) is reported to be about 50 mg per capita/day and the amount of DHA is 80 mg per capita/day. The two main sources are fish and poultry. 32 It has been estimated that the present Western diet is "deficient" in omega-3 fatty acids with a ratio of omega-6 to omega-3 of 15–20/1, instead of 1/1, as is the case with wild animals and, presumably, human beings.7–11,23,33–35 Thus, an absolute and relative change of omega-6 and omega-3 in the food supply of Western societies has occurred over the last 100 years. A balance existed between omega-6 and omega-3 for millions of years during the long evolutionary history of the genus Homo, and genetic changes occurred partly in response to these dietary influences. During evolution, omega-3 fatty acids were found in all foods consumed: meat, wild plants, eggs, fish, nuts, and berries. Recent studies by Cordain et al.36 on wild animals confirm the original observations of Crawford and Sinclair et al.33,37 However, rapid dietary changes over short periods of time as have occurred over the past 100–150 years is a totally new phenomenon in human evolution 23,26,38–40 (Table 10.5).



Mammalian cells cannot convert omega-6 to omega-3 fatty acids because they lack the converting enzyme, omega-3 desaturase. Linoleic acid (LA) and alphalinolenic acid (ALA) and their long-chain derivatives are important components of animal and plant cell membranes. These two classes of essential fatty acids (EFA) are not interconvertible, are metabolically and functionally distinct, and often have important opposing physiological functions. The balance of EFA is important for good health and normal development. When humans ingest fish or fish oil, the EPA and docosahexaenoic acid (DHA) from the diet partially replace the omega-6 fatty acids, especially arachidonic acid (AA), in the membranes of probably all cells, but especially in the membranes of platelets, erythrocytes, neutrophils, monocytes, and liver cells. 8 Whereas cellular proteins are genetically determined, the polyunsaturated fatty acid (PUFA) composition of cell membranes is to a great extent dependent on the dietary intake. AA and EPA are the parent compounds for eicosanoid production (Table 10.6, Figure 10.2).




Because of the increased amounts of omega-6 fatty acids in the Western diet, the eicosanoid metabolic products from AA, specifically prostaglandins, thromboxanes,leukotrienes, hydroxy fatty acids, and lipoxins, are formed in larger quantities than those formed from omega-3 fatty acids, specifically EPA. The eicosanoids from AA are biologically active in very small quantities, and if they are formed in large amounts, they contribute to the formation of thrombus and atheromas; to allergic and inflammatory disorders, particularly in susceptible people; and to proliferation of cells. Thus, a diet rich in omega-6 fatty acids shifts the physiological state to one that is prothrombotic and proaggregatory, with increases in blood viscosity, vasospasm,and vasoconstriction and decreases in bleeding time. Bleeding time is decreased in groups of patients with hypercholesterolemia, 41 hyperlipoproteinemia, 42 myocardial infarction, other forms of atherosclerotic disease, and diabetes (obesity and hypertriglyceridemia). Bleeding time is longer in women than in men and longer in young than in old people. There are ethnic differences in bleeding time that appear to be related to diet. Table 10.7 shows that the higher the ratio of omega-6/omega-3 fatty acids in platelet phospholipids, the higher the death rate from cardiovascular disease. 43



The antithrombotic aspects and the effects of different doses of fish oil on the prolongation of bleeding time were investigated by Saynor et al. 44 A dose of 1.8 g/d EPA did not result in any prolongation in bleeding time, but at 4 g/d the bleeding time increased and the platelet count decreased without any adverse effects. In human studies there has never been a case of clinical bleeding, even in patients undergoing angioplasty while they were on fish oil supplements. 45 There is substantial agreement that ingestion of fish or fish oils has the following effects: platelet aggregation to epinephrine and collagen is inhibited, thromboxane A2 production is decreased, whole blood viscosity is reduced, and erythrocyte membrane fluidity is increased.46–49 Fish oil ingestion increases the concentration of plasminogen activator and decreases the concentration of plasminogen activator inhibitor 1 (PAI-1). 50 In vitro studies have demonstrated that PAI-1 is synthesized and secreted in hepatic cells in response to insulin, and population studies indicate a strong correlation between insulinemia and PAI-1 levels. In patients with types IIb and IV hyperlipoproteinemia and in another double-blind clinical trial involving 64 men aged 35 to 40 years, ingestion of omega-3 fatty acids decreased the fibrinogen concentration. 51 Two other studies did not show a decrease in fibrinogen, but in one, a small dose of cod liver oil was used, 52 and in the other the study consisted of normal volunteers and was of short duration. A recent study noted that fish and fish oil increase fibrinolytic activity, indicating that 200 g/day of lean fish or 2 g of omega-3 EPA and DHA improve certain hematologic parameters implicated in the etiology of cardiovascular disease. 53

Ingestion of omega-3 fatty acids not only increases the production of prostaglandin I3 (PGI3), but also of PGI2 in tissue fragments from the atrium, aorta, and saphenous vein obtained at surgery in patients who received fish oil two weeks prior to surgery. 54 Omega-3 fatty acids inhibit the production of platelet-derived growth factor (PDGF) in bovine endothelial cells. 55 PDGF is a chemoattractant for smooth muscle cells and a powerful mitogen. Thus, the reduction in its production by endothelial cells, monocytes/macrophages, and platelets could inhibit both the migration and proliferation of smooth muscle cells, monocytes/macrophages, and fibroblasts in the arterial wall. Insulin increases the growth of smooth muscle cells, leading to increased risk for the development of atherosclerosis. Omega-3 fatty acids increase endothelium-derived relaxing factor (EDRF).56 EDRF (nitric oxide) facilitates relaxation in large arteries and vessels. In the presence of EPA, endothelial cells in culture increase the release of relaxing factor, indicating a direct effect of omega-3 fatty acids on the cells.

Many experimental studies have provided evidence that incorporation of alternative fatty acids into tissues may modify inflammatory and immune reactions and that omega-3 fatty acids, in particular, are potent therapeutic agents for inflammatory diseases. Supplementing the diet with omega-3 fatty acids (3.2 g EPA and 2.2 g DHA) in normal subjects increased the EPA content in neutrophils and monocytes more than sevenfold without changing the quantities of AA and DHA. The antiinflammatory effects of fish oils are partly mediated by inhibiting the 5-lipoxygenase pathway in neutrophils and monocytes and inhibiting the leukotriene B4 (LTB4)- mediated function of LTB5 (Figure 10.2). 57,58 Studies show that omega-3 fatty acids influence interleukin metabolism by decreasing IL-1B and IL-6. 59–62 Inflammation plays an important role in both the initiation of atherosclerosis and the development of atherothrombotic events. 63 An early step in the atherosclerotic process is the adhesion of monocytes to endothelial cells. Adhesion is mediated by leukocyte and vascular cell adhesion molecules (CAMs) such as selectins, integrins, vascular cell adhesion molecule 1 (VCAM-1), and intercellular adhesion molecule 1 (ICAM-1).64 The expression of E-selectin, ICAM-1 and VCAM-1, which is relatively low in normal vascular cells, is upregulated in the presence of various stimuli, including cytokines and oxidants. This increased expression promotes the adhesion of monocytes to the vessel wall. The monocytes subsequently migrate across the endothelium into the vascular intima, where they accumulate to form the initial lesions of atherosclerosis. Atherosclerotic plaques have been shown to have increased CAM expression in animal models and human studies. 65–68 A balance between the omega-6 and omega-3 fatty acids is a more physiologic state in terms of gene expression, 69 eicosanoid metabolism, and cytokine production.

Further support for the need to balance the omega-6/omega-3 EFA comes from the studies of Ge et al.70 and Kang et al.71 The study by Ge et al. clearly shows the ability of both normal rat cardiomyocytes and human breast cancer cells in culture to form all the omega-3’s from omega-6 fatty acids when fed the cDNA encoding omega-3 fatty acid desaturase obtained from the roundworm C. elegans. The omega-3 desaturase efficiently and quickly converted the omega-6 fatty acids that were fed to the cardiomyocytes in culture to the corresponding omega-3 fatty acids. Thus, omega-6 LA was converted to omega-3 ALA, and AA was converted to EPA, so that at equilibrium, the ratio of omega-6 to omega-3 PUFA was close to 1/1.71 Further studies demonstrated that the cancer cells expressing the omega-3 desaturase underwent apoptotic death, whereas the control cancer cells with a high omega-6/omega-3 ratio continued to proliferate.70 More recently, Kang et al. showed that transgenic mice expressing the C. elegans fat-1 gene encoding an omega-3 fatty acid desaturase are capable of producing omega-3 from omega-6 fatty acids, leading to enrichment of omega-3 fatty acids with reduced levels of omega-6 fatty acids in almost all organs and tissues, including muscles and milk, with no need of dietary omega-3 fatty acid supply.72 This discovery provides a unique tool and new opportunities for omega-3 research and raises the potential of production of fat-1 transgenic livestock as a new and ideal source of omega-3 fatty acids to meet the human nutritional needs.

(continued below)

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Source: Phytochemicals: Nutrient-Gene Interactions,
Mark S. Meskin (Editor),
CRC; 1 edition (February 22, 2006)
pp 137-159

CLINICAL INTERVENTION STUDIES AND THE OMEGA-6/OMEGA-3 EFA BALANCE

The Lyon Heart Study was a dietary intervention study in which a modified diet of Crete (the experimental diet) was compared with the prudent diet, or Step I American Heart Association Diet (the control diet).73–75 The experimental diet provided a ratio of LA to ALA of 4/1. This ratio was achieved by substituting olive oil and canola(oil) margarine for corn oil. Since olive oil is low in LA, whereas corn oil is high (8% and 61%, respectively) the ALA incorporation into cell membranes was increased. Cleland et al.76 have shown that olive oil increases the incorporation of omega-3 fatty acids, whereas the LA from corn oil competes. The ratio of 4/1 of LA/ALA led to a 70% decrease in total mortality at the end of two years.73

The Gruppo Italiano per lo Studio della Sopravvivenza nell’Infarto miocardico (GISSI) Prevenzione Trial participants were on a traditional Italian diet plus 850 to 882 mg of omega-3 fatty acids at a ratio of 2/1 EPA to DHA.77 The supplemented group had a decrease in sudden cardiac death by 45%. Although there are no dietary data on total intake for omega-6 and omega-3 fatty acids, the difference in sudden death is most likely due to the increase of EPA and DHA and a decrease of AA in cell membrane phospholipids. Prostaglandins derived from AA are proarrhythmic, whereas the corresponding prostaglandins from EPA are not.78 In the Diet and Reinfarction Trial (DART), Burr et al. reported a decrease in sudden death in the group that received fish advice or took fish oil supplements relative to the group that did not.79 Similar results have been obtained by Singh et al.80,81 Studies carried out in India indicate that the higher ratio of Linoleic acid (18:2n-6 ) to A-Linolenic acid (18:3n-3 ) equalling 20/1 in their food supply led to increases in the prevalence of non-insulin dependent diabetes mellitus (NIDDM) in the population, whereas a diet with a ratio of 6/1 led to decreases.82

James and Cleland have reported beneficial effects in patients with rheumatoid arthritis 83 and Broughton has shown beneficial effects in patients with asthma by changing the background diet.84 James and Cleland evaluated the potential use of omega-3 fatty acids within a dietary framework of an omega-6/omega-3 ratio of 3–4/1 by supplying 4 gm of EPA+DHA and using flaxseed oil rich in ALA. In their studies, the addition of 4 gm EPA and DHA in the diet produced a substantial inhibition of production of IL-1B and TNF when mononuclear cell levels of EPA were equal to or greater than 1.5% of total cell phospholipid fatty acids, which correlated with a plasma phospholipid EPA level equal to or greater than 3.2%. These studies suggest the potential for complementarity between drug therapy and dietary choices that increased intake of omega-3 fatty acids and decreased intake of omega-6 fatty acids may lead to drug-sparing effects. Therefore, future studies need to address the fat composition of the background diet, and the issue of concurrent drug use. A diet rich in omega-3 fatty acids and poor in omega-6 fatty acids provides the appropriate background biochemical environment in which drugs function.

Asthma is a mediator-driven inflammatory process in the lungs and the most common chronic condition in childhood. The leukotrienes and prostaglandins are implicated in the inflammatory cascade that occurs in asthmatic airways. There is evidence of airway inflammation even in newly diagnosed asthma patients within 2 to 12 months after their first symptoms.85 Among the cells involved in asthma are mast cells, macrophages, eosinophils, and lymphocytes. The inflammatory mediators include cytokines and growth factors (peptide mediators) as well as the eicosanoids, which are the products of AA metabolism, which are important mediators in the underlying inflammatory mechanisms of asthma (Figure 10.2, Table 10.8).



Leukotrienes and prostaglandins appear to have the greatest relevance to the pathogenesis of asthma. The leukotrienes are potent inducers of bronchospasm, airway edema, mucus secretion, and inflammatory cell migration, all of which are important to the asthmatic symptomatology. Broughton et al.84 studied the effect of omega-3 fatty acids at a ratio of omega-6/omega-3 of 10/1 to 5/1 in an asthmatic population in ameliorating methacholine-induced respiratory distress. With low omega-3 ingestion, methacholine-induced respiratory distress increased. With high omega-3 fatty acid ingestion, alterations in urinary 5-series leukotriene excretion predicted treatment efficacy and a dose change in >40% of the test subjects (responders), whereas the non-responders had a further loss in respiratory capacity. A urinary ratio of 4-series to 5-series of <1 induced by omega-3 fatty acid ingestion may predict respiratory benefit.

Bartram et al.86,87 carried out two human studies in which fish oil supplementation was given in order to suppress rectal epithelial cell proliferation and PGE2 biosynthesis. This was achieved when the dietary omega-6/omega-3 ratio was 2.5/1 but not with the same absolute level of fish oil intake and an omega-6/omega-3 ratio of 4/1. More recently, Maillard et al. reported their results on a case control study.88 They determined omega-3 and omega-6 fatty acids in breast adipose tissue and relative risk of breast cancer. They concluded, "our data based on fatty acid levels in breast adipose tissue (which reflect dietary intake) suggest a protective effect of omega-3 fatty acids on breast cancer risk and support the hypothesis that the balance between omega-3 and omega-6 fatty acids plays a role in breast cancer."

Psychologic stress in humans induces the production of proinflammatory cytokines such as interferon gamma (IFNy), tumor necrosis factor ~ (TNF~), IL-6, and IL-10. An imbalance of omega-6 and omega-3 PUFA in the peripheral blood causes an overproduction of proinflammatory cytokines. There is evidence that changes in fatty acid composition are involved in the pathophysiology of major depression. Changes in serotonin (5-HT) receptor number and function caused by changes in PUFA provide the theoretical rationale connecting fatty acids with the current receptor and neurotransmitter theories of depression.89–91 The increased Arachidonic acid (20:4n-6 )/Eicosapentaenoic acid (EPA) (20:5n-3 ) ratio and the imbalance in the omega-6/omega-3 PUFA ratio in major depression may be related to the increased production of proinflammatory cytokines and eicosanoids in that illness.89 There are a number of studies evaluating the therapeutic effect of EPA and DHA in major depression. Stoll and colleagues have shown that EPA and DHA prolong remission, that is, reduce the risk of relapse in patients with bipolar disorder.92,93

The above clinical studies in patients with cardiovascular disease, arthritis, asthma, cancer, and mental illness clearly indicate the need to balance the omega-6/omega-3 fatty acid intake for prevention and during treatment. The scientific evidence is strong for decreasing the omega-6 and increasing the omega-3 intake to improve health throughout the lifecycle.94 The scientific basis for the development of a public policy to develop dietary recommendations for essential fatty acids, including a balanced omega-6/omega-3 ratio is robust. 95


OMEGA-3 FATTY ACIDS AND GENE EXPRESSION

Previous studies have shown that fatty acids released from membrane phospholipids by cellular phospholipases, or made available to the cell from the diet or other aspects of the extracellular environment, are important cell-signalling molecules.96 They can act as second messengers or substitute for the classical second messengers of the inositide phospholipid and the cyclic AMP signal transduction pathways.96 They can also act as modulator molecules mediating responses of the cell to extracellular signals.96 Recently it has been shown that fatty acids rapidly and directly alter the transcription of specific genes.97

Table 10.9 and Table 10.10 summarize the effects of various PUFA on gene expression. In the case of enzymes involved in carbohydrate and lipid metabolism, both omega-3 and omega-6 fatty acids appear to suppress the genes that encode for several enzymes (Table 10.9), whereas saturated, trans-, and monounsaturated fatty acids fail to suppress. DHA appears more potent in its effect than other PUFA. Omega-6 and omega-3 fatty acids and monounsaturated fatty acids induce acyl-CoA oxidase, the enzyme involved in beta-oxidation, but here again, DHA appears to be more potent.

In studies of inflammatory cytokines, such as IL-1B, both EPA and DHA suppress IL-1B mRNA whereas AA does not, and the same effect appears in studies on growth related early response gene expression and growth factor (Table 10.10). In the case of VCAM, AA has a modest suppressing effect relative to DHA. The latter situation may explain the protective effect of fish oil toward colonic carcinogenesis, since EPA and DHA did not stimulate protein kinase C.111 PUFA regulation of gene expression extends beyond the liver and includes genes such as adipocyte glucose transporter-4, lymphocyte stearoyl-CoA desaturase 2 in the brain, peripheral monocytes (IL-1B, and VCAM-1), and platelets (PDGF)110 (Table 10.9 and Table 10.10). Whereas some of the transcriptional effects of PUFA appear to be mediated by eicosanoids, the PUFA suppression of lipogenic and glycolytic genes is independent of eicosanoid synthesis and appears to involve a nuclear mechanism directly modified by PUFA. Because of their coordinate or opposing effects, both classes of PUFA are needed in the proper amounts for normal growth and development. Although, so far the studies in infants have concentrated on the effects of PUFA on retinal and brain phospholipid composition and intelligence quotient (IQ),112,113 motor development is very much dependent on intermediary metabolism and on overall normal metabolism, both of which are influenced by fatty acid biosynthesis and carbohydrate metabolism.

The amounts of PUFA found in breast milk in mothers fed diets consistent with our evolution should serve as a guide to determine omega-6 and omega-3 fatty acid requirements during pregnancy, lactation, and infant feeding. Of interest is the fact that saturated, monounsaturated, and trans fatty acids do not exert any suppressive action on lipogenic or glycolytic gene expression, which is consistent with their high content in human milk serving primarily as sources of energy. Because nutrients influence gene expression, and many chronic diseases begin in utero or in infancy, proper dietary intake of PUFA, even prior to pregnancy may be essential, as shown for folate deficiency in the development of neural tube defects.




DIET–GENE INTERACTIONS: GENETIC VARIATION AND OMEGA-6 AND OMEGA-3 FATTY ACID INTAKE IN THE RISK FOR CARDIOVASCULAR DISEASE

As discussed above, leukotrienes are inflammatory mediators generated from AA by the enzyme 5-lipoxygenase (Figure 10.2). Since atherosclerosis involves arterial inflammation, Dwyer et al. hypothesized that a polymorphism in the 5-lipoxygenase gene promoter could relate to atherosclerosis in humans, and that this effect could interact with the dietary intake of competing 5-lipoxygenase substrates.114 The study consisted of 470 healthy middle-aged women and men from the Los Angeles Atherosclerosis Study, randomly sampled. The investigators determined 5-lipoxygenase genotypes, carotid-artery intima thickness, markers of inflammation, C-reactive protein (CRP), interleukin-6 (IL-6), dietary AA, EPA, DHA, LA, and ALA, with the use of six 24-hour recalls of food intake. The results showed that 5-lipoxygenase variant genotypes were found in 6% of the cohort. Mean intima-media thickness adjusted for age, sex, height, and racial or ethnic group was increased by 80 ± 19um from among the carriers of two variant alleles as compared with the carrier of the common (wild-type) allele. In multivariate analysis, the increase in intima-media thickness among carriers of two variant alleles (62 um, p = 0.001) was similar in this cohort to that associated with diabetes (64 ìm, p = 0.01), the strongest common cardiovascular risk factor. Increased dietary AA significantly enhanced the apparent atherogenic effect of genotype, whereas increased dietary intake of omega-3 fatty acids EPA and DHA blunted this effect. Furthermore, the plasma level of CRP of two variant alleles was increased by a factor of 2, as compared with that among carriers of the common allele. Thus, genetic variation of 5-lipoxygenase identifies a subpopulation with increased risk for atherosclerosis. The diet–gene interaction further suggests that dietary omega-6 fatty acids promote, whereas marine omega-3 fatty acids EPA and DHA inhibit, leukotriene-mediated inflammation that leads to atherosclerosis in this subpopulation.

The prevalence of variant genotypes did differ across racial and ethnic groups with higher prevalence among Asians or Pacific Islanders (19.4%), blacks (24%), and other racial or ethnic groups (18.2%) than among Hispanic subjects (3.6%) and non-Hispanic whites (3.1%). Increased intima-mediated thickness was significantly associated with intake of both AA and LA among carriers of the two variant alleles, but not among carriers of the common alleles. In contrast, the intake of marine omega-3 fatty acids was significantly and inversely associated with intima-media thickness only among carriers of the two variant alleles. Diet–gene interactions were specific to these fatty acids and were not observed for dietary intake of monounsaturated, saturated fat, or other measured fatty acids. The study constitutes evidence that genetic variation in an inflammatory pathway — in this case the leukotriene pathway — can trigger atherogenesis in humans. These findings could lead to new dietary and targeted molecular approaches to the prevention and treatment of cardiovascular disease according to genotype, particularly in the populations of non-European descent.

CONCLUSIONS

• Evidence from studies on the evolutionary aspects of diet, modern day hunter-gatherers, and traditional diets indicate that human beings evolved on a diet in which the ratio of omega-6/omega-3 EFA was about 1, whereas in the Western diets the ratio is 15/1 to 16.7/1. Agribusiness and modern agriculture have led to decreases in omega-3 fatty acids and increases in omega-6 fatty acids. Such practices have led to excessive amounts of omega-6 fatty acids, upsetting the balance that was characteristic during evolution when our genes were programmed to respond to diet and other aspects of the environment.
  
  
• LA and ALA are not interconvertible and compete for the rate-limiting 6-desaturase in the synthesis of long-chain PUFA.
  
  
• AA (omega-6) and EPA (omega-3) are the parent compounds for the production of eicosanoids. Eicosanoids from AA have opposing properties from those of EPA. An increase in the dietary intake of omega-6 EFA changes the physiological state to a prothrombotic, proconstrictive, and proinflammatory state.
  
  
• Many of the chronic conditions — cardiovascular disease, diabetes, cancer, obesity, autoimmune diseases, rheumatoid arthritis, asthma, and depression — are associated with increased production of thromboxane A2 (TXA2), leukotriene B4 (LTB4), IL-1B, IL-6, tumor necrosis factor (TNF), and C-reactive protein. All these factors increase by increases in omega-6 fatty acid intake and decrease by increases in omega-3 fatty acid intake, either ALA or EPA and DHA. EPA and DHA are more potent, and most studies have been carried out using EPA and DHA.
  
  
• In the secondary prevention of cardiovascular disease, a ratio of 4/1 was associated with a 70% decrease in total mortality. A ratio of 2.5/1 reduced rectal cell proliferation in patients with colorectal cancer, whereas a ratio of 4/1 with the same amount of omega-3 PUFA had no effect. The lower omega-6/omega-3 ratio in women with breast cancer was associated with decreased risk. A ratio of 2–3/1 suppressed inflammation in patients with rheumatoid arthritis, and a ratio of 5/1 had a beneficial effect on patients with asthma, whereas a ratio of 10/1 had adverse consequences. These studies indicate that the optimal ratio may vary with the disease under consideration. This is consistent with the fact that chronic diseases are multigenic and multifactorial. Therefore, it is quite possible that the therapeutic dose of omega-3 fatty acids will depend on the degree of severity of disease resulting from the genetic predisposition.
  
  
• Studies show that the background diet, when balanced in omega-6/omega-3, decreases the drug dose. It is therefore essential to decrease the omega-6 intake while increasing the omega-3 in the prevention and management of chronic disease. Furthermore, the balance of omega-6 and omega-3 fatty acids is very important for homeostasis and normal development. The ratio of omega-6 to omega-3 EFA is an important determinant of health, because both omega-6 and omega-3 fatty acids influence gene expression. Recent studies on diet–gene interaction further suggest that dietary omega-6 fatty acids promote, whereas marine omega 3 fatty acids EPA and DHA inhibit leukotriene-mediated inflammation that leads to atherosclerosis.

[datBtrue]

Source: Phytochemicals: Nutrient-Gene Interactions,
Mark S. Meskin (Editor),
CRC; 1 edition (February 22, 2006)
pp 137-159

REFERENCES

1. Simopoulos, A.P. and Childs, B., Eds., Genetic Variation and Nutrition, vol. 63, World
Rev. Nutr. Diet., Karger, Basel, 1990.

2. Simopoulos, A.P., Herbert, V., and Jacobson, B., The Healing Diet: How to Reduce
Your Risks and Live a Longer and Healthier Life If You Have a Family History of
Cancer, Heart Disease, Hypertension, Diabetes, Alcoholism, Obesity, Food Allergies,
Macmillan Publishers, New York, 1995.

3. Simopoulos, A.P. and Nestel, P.J., Eds., Genetic Variation and Dietary Response, vol.
80, World Rev. Nutr. Diet., Karger, Basel, 1997.

4. Simopoulos, A.P. and Pavlou, K.N., Eds., Nutrition and Fitness 1: Diet, Genes,
Physical Activity and Health, vol. 89, World Rev. Nutr. Diet., Karger, Basel, 2001.

5. Simopoulos, A.P., Genetic variation and dietary response: nutrigenetics/nutrigenomics,
Asian Pacific J. Clin. Nutr., 11(S6), S117, 2002.

6. Simopoulos, A.P. and Ordovas J., Eds., Nutrigenetics and Nutrigenomics, vol. 93,
World Rev. Nutr. Diet., Karger, Basel, 2004.

7. Eaton, S.B. and Konner, M., Paleolithic nutrition. A consideration of its nature and
current implications. New Engl. J. Med., 312, 283, 1985.

8. Simopoulos, A.P., Omega-3 fatty acids in health and disease and in growth and
development, Am. J. Clin. Nutr., 54, 438, 1991.

9. Simopoulos, A.P., Genetic variation and evolutionary aspects of diet, in Antioxidants
in Nutrition and Health, Papas, A., Ed., CRC Press, Boca Raton, FL, 65, 1999.

10. Simopoulos, A.P., Evolutionary aspects of omega-3 fatty acids in the food supply,
Prostaglandins, Leukotrienes Essential Fatty Acids, 60(5&6), 421, 1999.

11. Simopoulos, A.P., New products from the agri-food industry: the return of n-3 fatty
acids into the food supply, Lipids 34(suppl), S297, 1999.

12. Cordain, L., Cereal grains: humanity’s double-edged sword, World Rev. Nutr. Diet.,
84, 19, 1999.

13. Simopoulos, A.P., Ed., Plants in Human Nutrition, vol. 77, World Rev. Nutr. Diet.,
Karger, Basel, 1995.

14. Zeghichi, S., Kallithraka, S., and Simopoulos, A.P., Nutritional composition of
molokhia (Corchorus olitorius) and stamnagathi (Cicorium spinosum), World Rev.
Nutr. Diet., 91, 1, 2003.

15. Zeghichi, S., et al., The nutritional composition of selected wild plants in the diet of
Crete, World Rev. Nutr. Diet., 91, 22, 2003.

16. Simopoulos, A.P., Omega-3 fatty acids and antioxidants in edible wild plants, Biol.
Research, 37(2), 263, 2004.

17. Simopoulos, A.P., Ed., Evolutionary Aspects of Nutrition and Health. Diet, Exercise,
Genetics and Chronic Disease, vol. 84, World Rev Nutr Diet., Karger, Basel, 1999.

18. Fanaian, M., et al., The effect of modified fat diet on insulin resistance and metabolic
parameters in type II diabetes, Diabetologia, 39(suppl 1), A7, 1996.

19. Simopoulos, A.P., Is insulin resistance influenced by dietary linoleic acid and trans
fatty acids? Free Rad. Biol. & Med., 17(4), 367, 1994.

20. Simopoulos, A.P., Fatty acid composition of skeletal muscle membrane phospholipids,
insulin resistance and obesity, Nutr. Today, 2, 12, 1994.

21. Simopoulos, A.P. and Robinson, J., The Omega Diet. The Lifesaving Nutritional
Program Based on the Diet of the Island of Crete. HarperCollins, New York, 1999.

22. Eaton, S.B., Konner, M., and Shostak, M., Stone agers in the fast lane: chronic
degenerative diseases in evolutionary perspective, Am. J. Med., 84, 739, 1988.

23. Eaton, S.B., et al., Dietary intake of long-chain polyunsaturated fatty acids during
the Paleolithic, World Rev. Nutr. Diet., 83, 12, 1998.

24. Leaf, A. and Weber, P.C., A new era for science in nutrition, Am. J. Clin. Nutr., 45,
1048, 1987.

25. Simopoulos, A.P., The Mediterranean diet: Greek column rather than an Egyptian
pyramid, Nutr. Today, 30(2), 54, 1995.

26. Simopoulos, A.P., Overview of evolutionary aspects of w3 fatty acids in the diet,
World Rev. Nutr. Diet., 83, 1, 1998.

27. Simopoulos, A.P., Evolutionary aspects of diet and essential fatty acids, World Rev.
Nutr. Diet., 88, 18, 2001.

28. Simopoulos, A.P., Evolutionary aspects of diet: Fatty acids, insulin resistance and
obesity, in Obesity: New Directions in Assessment and Management, VanItallie, T.B.
and Simopoulos, A.P., Eds., Charles Press, Philadelphia, 1995, 241.

29. Simopoulos, A.P., Trans fatty acids, Handbook of Lipids in Human Nutrition, Spiller,
G.A., Ed., CRC Press, Boca Raton, FL, 1995, 91.

30. Hunter, J.E., Omega-3 fatty acids from vegetable oils, in Biological Effects and
Nutritional Essentiality. Series A: Life Sciences, vol. 171, Galli, C. and Simopoulos,
A.P., Eds., Plenum Press, New York, 1989, 43.

31. Litin, L. and Sacks, F., Trans-fatty-acid content of common foods, N. Engl. J. Med.,
329(26), 1969.

32. Raper, N.R., Cronin, F.J., and Exler, J., Omega-3 fatty acid content of the US food
supply, J. Am. College Nutr. 11(3), 304, 1992.

33. Crawford, M.A., Fatty acid ratios in free-living and domestic animals, Lancet, i, 1329,
1968.

34. Crawford, M.A., Gale, M.M., and Woodford, M.H., Linoleic acid and linolenic acid
elongation products in muscle tissue of Syncerus caffer and other ruminant species,
Biochem. J., 115, 25, 1969.

35. Ledger, H.P., Body composition as a basis for a comparative study of some East
African animals, Symp. Zool. Soc. London, 21, 289, 1968.

36. Cordain, L., et al., The fatty acid composition of muscle, brain, marrow and adipose
tissue in elk: evolutionary implications for human dietary requirements, World Rev.
Nutr. Diet., 83, 225, 1998.

37. Sinclair, A.J., Slattery, W.J., and O’Dea, The analysis of polyunsaturated fatty acids
in meat by capillary gas-liquid chromotography, J. Food Sci. Agric., 33, 771, 1982.

38. Sugano, M. and Hirahara, F., Polyunsaturated fatty acids in the food chain in Japan,
Am. J. Clin. Nutr., 71(suppl), 189S, 2000.

39. Pella, D., et al., Effects of an Indo-Mediterranean diet on the omega-6/omega-3 ratio
in patients at high risk of coronary artery disease: The Indian paradox, World Rev.
Nutr. Diet., 92, 74, 2003.

40. Sanders, T.A.B., Polyunsaturated fatty acids in the food chain in Europe, Am. J. Clin.
Nutr., 71(suppl), S176, 2000.

41. Brox, J.H., et al., Effects of cod liver oil on platelets and coagulation in familial
hypercholesterolemia (type IIa), Acta Med. Scand., 213, 137, 1983.

42. Joist, J.H., Baker, R.K., and Schonfeld, G., Increased in vivo and in vitro platelet
function in type II- and type IV-hyperlipoproteinemia, Thromb. Res., 15, 95, 1979.

43. Weber, P.C., Are we what we eat? Fatty acids in nutrition and in cell membranes:
cell functions and disorders induced by dietary conditions, Report No. 4, Svanoy
Foundation, Svanoybukt, Norway, 1989, 9.

44. Saynor, R., Verel. D., and Gillott, T., The long term effect of dietary supplementation
with fish lipid concentrate on serum lipids, bleeding time, platelets and angina,
Atherosclerosis, 50, 3, 1984.

45. Dehmer, G.J., et al., Reduction in the rate of early restenosis after coronary angioplasty
by a diet supplemented with n-3 fatty acids, N. Engl. J. Med., 319, 733, 1988.

46. Bottiger, L.E., Dyerberg, J., and Nordoy, A., Eds., N-3 Fish oils in clinical medicine.
J. Intern. Med, 225(suppl 1), 1, 1989.

47. Cartwright, I.J., et al., The effects of dietary w-3 polyunsaturated fatty acids on
erythrocyte membrane phospholipids, erythrocyte deformability, and blood viscosity
in healthy volunteers, Atherosclerosis, 55, 267, 1985.

48. Lewis, R.A., Lee, T.H., and Austen, K.F., Effects of omega-3 fatty acids on the
generation of products of the 5-lipoxygenase pathway, in Health Effects of Polyunsaturated
Fatty Acids in Seafoods, Simopoulos, A.P., Kifer, R.R., and Martin, R.E.,
Eds., Academic Press, Orlando, 1986, 227.

49. Weber, P.C. and Leaf, A., Cardiovascular effects of w3 fatty acids: atherosclerotic
risk factor modification by w3 fatty acids, in Health Effects of w3 Polyunsaturated
Fatty Acids in Seafoods, Simopoulos, A.P., et al., Eds., vol. 66, World Rev. Nutr. Diet.,
Karger, Basel, 1991, 218.

50. Barcelli, U.O., Glass-Greenwalt, P., and Pollak,V.E., Enhancing effect of dietary
supplementation with omega-3 fatty acids on plasma fibrinolysis in normal subjects,
Thromb. Res., 39, 307, 1985.

51. Radack, K., Deck, C., and Huster, G., Dietary supplementation with low-dose fish
oils lowers fibrinogen levels: a randomized, double-blind controlled study, Ann.
Intern. Med., 111, 757, 1989.

52. Sanders, T.A.B., Vickers, M., and Haines, A.P., Effect on blood lipids and hemostasis
of a supplement of cod-liver oil, rich in eicosapentaenoic and docosahexaenoic acids,
in healthy young men, Clin. Sci., 61, 317, 1981.

53. Brown, A.J. and Roberts, D.C.K., Fish and fish oil intake: effect on hematological
variables related to cardiovascular disease, Thromb. Res., 64, 169, 1991.

54. De Caterina, R., et al., Vascular prostcyclin is increased in patients ingesting n-3
polyunsaturated fatty acids prior to coronary artery bypass surgery, Circulation, 82,
428, 1990.

55. Fox, P.L. and Dicorleto, P.E., Fish oils inhibit endothelial cell production of a plateletderived
growth factor-like protein, Science, 241, 453, 1988.

56. Shimokawa, H. and Vanhoutte, P.M., Dietary cod-liver oil improves endothelium
dependent responses in hypercholesterolemic and atherosclerotic porcine coronary
arteries, Circulation, 78, 1421, 1988.

57. Kremer, J.M., Jubiz, W., and Michalek, A., Fish-oil fatty acid supplementation in
active rheumatoid arthritis, Ann. Intern. Med., 106, 497, 1987.

58. Lee, T.H., et al., Effect of dietary enrichment with eicosapentaenoic and docosahexaenoic
acids on in vitro neutrophil and monocyte leukotriene generation and
neutrophil function, N. Engl. J. Med., 312, 1217, 1985.

59. Endres, S., et al., The effect of dietary supplementation with n-3 polyunsaturated
fatty acids on the synthesis of interleukin-1 and tumor necrosis factor by mononuclear
cells, N. Engl. J. Med., 320, 265, 1989.

60. Khalfoun, B., et al., Docosahexaenoic and eisosapentaenoic acids inhibit in vitro
human endothelial cell production of interleukin-6, in Eicosanoids and Other Bioactive
Lipids in Cancer, Inflammation, and Radiation Injury 2, Honn, K.V., et al.,
Eds, Plenum Press, New York, 1997.

61. Kremer, J.M., Lawrence, D.A., and Jubiz,W., Different doses of fish-oil fatty acid
ingestion in active rheumatoid arthritis: a prospective study of clinical and immunological
parameters, in Dietary w3 and w6 Fatty Acids: Biological Effects and Nutritional
Essentiality, Galli, C. and Simopoulos, A.P., Eds., Plenum Publishing, New
York, 1989, 343.

62. Robinson, D.R. and Kremer, J.M., Summary of Panel G: rheumatoid arthritis and
inflammatory mediators, World Rev. Nutr. Diet., 66, 44, 1991.

63. Ross, R., Atherosclerosis — an inflammatory disease, N. Engl. J. Med., 340, 115,
1999.

64. Springer, T.A., Traffic signals for lymphocyte recirculation and leukocyte emigration:
the multistep paradigm, Cell, 76, 301, 1994.

65. Davies, M.J., et al., The expression of the adhesion molecules ICAM-1, VCAM-1,
PECAM, and E-selectin in human atherosclerosis, J. Pathol., 171, 223, 1993.

66. O’Brien, K.D., et al., Vascular cell adhesion molecule-1 is expressed in human
coronary atherosclerotic plaques: implications for the mode of progression of
advanced coronary atherosclerosis, J. Clin. Invest. 92, 945, 1993.

67. Poston, R.N., et al., Expression of intercellular adhesion molecule-1 in atherosclerotic
plaques, Am. J. Pathol. 140, 665, 1992.

68. Richardson, M., et al., Increased expression in vivo of VCAM-1 and E-selectin by
the aortic endothelium of normolipemic and hyperlipemic diabetic rabbits, Arterioscler.
Thromb. 14, 760, 1994.

69. Simopoulos, A.P., The role of fatty acids in gene expression: health implications,
Ann. Nutr. Metab., 40, 303, 1996.

70. Ge, Y-L., et al., Effects of adenoviral transfer of Caenorhabditis elegans n-3 fatty acid
desaturase on the lipid profile and growth of human breast cancer cells, Anticancer
Research, 22, 537, 2002.

71. Kang, Z.B., et al., Adenoviral transfer of Caenorhabditis elegans n-3 fatty acid
desaturase optimizes fatty acid composition in mammalian heart cells, Proc. Natl.
Acad. Sci. U.S.A., 98, 4050, 2001.

72. Kang, J.X., et al., Fat-1 mice convert n-6 to n-3 fatty acids, Nature, 427, 504, 2004.

73. de Lorgeril, M., et al., Mediterranean alpha-linolenic acid-rich diet in secondary
prevention of coronary heart disease, Lancet, 343, 1454, 1994.

74. de Lorgeril, M. and Salen, P., Modified Cretan Mediterranean diet in the prevention
of coronary heart disease and cancer, World Rev. Nutr. Diet., 87, 1, 2000.

75. Renaud, S., et al., Cretan Mediterranean diet for prevention of coronary heart disease.
Am. J. Clin. Nutr., 61(suppl), 1360S, 1995.

76. Cleland, L.G., et al., Linoleate inhibits EPA incorporation from dietary fish-oil supplements
in human subjects, Am. J. Clin. Nutr., 55, 395, 1992.

77. GISSI-Prevenzione Investigators, Dietary supplementation with n-3 polyunsaturated
fatty acids and vitamin E after myocardial infarction: results of the GISSI-Prevenzione
trial, Lancet, 354, 447, 1999.

78. Li, Y., Kang, J.X., and Leaf, A., Differential effects of various eicosanoids on the
contraction of cultured neonatal rat cardiomyocytes, Prostaglandins, 54, 511, 1997.

79. Burr, M.L., et al., Effect of changes in fat, fish and fibre intakes on death and
myocardial reinfarction: diet and reinfarction trial (DART), Lancet, 2, 757, 1989.

80. Singh, R.B. et al., Randomized controlled trial of cardioprotective diet in patients
with recent acute myocardial infarction: results of one year follow up, Brit. Med. J.,
304, 1015, 1992.

81. Singh, R.B., et al., Randomized, double-blind, placebo-controlled trial of fish oil and
mustard oil in patients with suspected acute myocardial infarction: the Indian experiment
of infarct survival — 4, Cardiovasc. Drugs Ther., 11, 485, 1997.

82. Raheja, B.S., et al., Significance of the n-6/n-3 ratio for insulin action in diabetes,
Ann. N.Y. Acad. Sci., 683, 258, 1993.

83. James, M.J. and Cleland, L.G., Dietary n-3 fatty acids and therapy for rheumatoid
arthritis, Semin. Arthritis Rheum., 27, 85, 1997.

84. Broughton, K.S., et al. Reduced asthma symptoms with n-3 fatty acid ingestion are
related to 5-series leukotriene production, Am. J. Clin. Nutr., 65(4), 1011, 1997.

85. Laitinen, L.A., Laitinen, A., and Haahtela, T., Airway mucosal inflammation even in
patients with newly diagnosed asthma, Am. Rev. Respir. Dis., 147(3), 697, 1993.

86. Bartram, H.-P., et al., Effects of fish oil on rectal cell proliferation, mucosal fatty
acids, and prostaglandin E2 release in healthy subjects, Gastroenterology, 105, 1317,
1993.

87. Bartram, H.-P., et al. Missing anti-proliferative effect of fish oil on rectal epithelium
in healthy volunteers consuming a high-fat diet: potential role of the n-3:n-6 fatty
acid ratio, Eur. J. Cancer Prev., 4, 231, 1995.

88. Maillard, V., et al., N-3 and n-6 fatty acids in breast adipose tissue and relative risk
of breast cancer in a case-control study in Tours, France, Int. J. Cancer, 98, 78, 2002.

89. Maes, M., et al., Fatty acid composition in major depression: decreased omega 3
fractions in cholesteryl esters and increased C20:4 omega 6/C20:5 omega 3 ratio in
cholesteryl esters and phospholipids, J. Affect Disord., 38(1), 35, 1996.

90. Maes, M., et al., Lower serum high-density lipoprotein cholesterol (HDL-C) in major
depression and in depressed men with serious suicidal attempts: relationship with
immune-inflammatory markers, Acta Psychiatr. Scand., 95(3), 212, 1997.

91. Peet, M., et al., Depletion of omega-3 fatty acid levels in red blood cell membranes
of depressive patients, Biol. Psychiatry, 43(5), 315, 1998.

92. Stoll, A.L., et al., Omega-3 fatty acids in bipolar disorder: a preliminary double-blind
placebo-controlled trial, Arch. Gen. Psychiatry 56(5), 407, 1999.

93. Locke, C.A. and Stoll, A.L., Omega-3 fatty acids in major depression, World Rev.
Nutr. Diet., 89, 173, 2001.

94. Simopoulos, A.P. and Cleland, L.G., Eds., Omega-6/Omega-3 Essential Fatty Acid
Ratio: The Scientific Evidence, vol. 92, World Rev. Nutr. Diet., Karger, Basel, 2003.

95. Simopoulos, A.P., N-3 fatty acids and human health: defining strategies for public
policy, Lipids, 36, S83, 2001.

96. Graber, R., Sumida, C., and Nunez, E.A., Fatty acids and cell signal transduction, J.
Lipid Mediat. Cell Signal, 9, 91, 1994.

97. Clarke, S.D. and Jump, D.B., Dietary polyunsaturated fatty acid regulation of gene
transcription, Annu. Rev. Nutr., 14, 83, 1994.

98. Clarke, S.D., Romsos, D.R., and Leveille, G.A., Differential effects of dietary methylesters
of long chain saturated and polyunsaturated fatty acids on rat liver and adipose
tissue lipogenesis, J. Nutr., 107, 1170, 1977.

99. Clarke, S.D., Armstrong, M.K., and Jump, D.B., Nutritional control of rat liver fatty
acid synthase and S14 mRNA abundance, J. Nutr., 120, 218, 1990.

100. Clarke, S.D. and Jump, D.B., Fatty acid regulation of gene expression: a unique role
for polyunsaturated fats, in Nutrition and Gene Expression, Berdanier, C. and Hargrove,
J.L., Eds., CRC Press, Boca Raton, FL, 1993, 227.

101. Clarke, S.D. and Jump, D.B., Polyunsaturated fatty acid regulation of hepatic gene
transcription, Lipids, 31(suppl), 7, 1996.

102. Jump, D.B., et al., Coordinate regulation of glycolytic and lipogenic gene expression
by polyunsaturated fatty acids, J. Lipid Res., 35, 1076, 1994.

103. Tebbey, P.W., et al., Arachidonic acid down-regulates the insulin-dependent glucose
transporter gene (Glut 4) in 3T3-L1 adipocytes by inhibiting transcription and enhancing
mRNA turnover, J. Biol. Chem., 269, 639, 1994.

104. Limatta, M., et al., Dietary PUFA interfere with the insulin glucose activation of Ltype
pyruvate kinase. Mol. Endocrinol., 8, 1147, 1994.

105. Ntambi, J.M., Dietary regulation of stearoyl-CoA desaturase I gene expression in
mouse liver, J. Biol. Chem., 267, 10925, 1991.

106. DeWillie, J.W. and Farmer, S.J., Linoleic acid controls neonatal tissue-specific
stearoyl-CoA desaturase mRNA levels, Biochim. Biophys. Acta., 1170, 291, 1993.

107. Sellmayer, A., Danesch, U., and Weber, P.C., Effects of different polyunsaturated
fatty acids on growth-related early gene expression and cell growth, Lipids, 31, S37,
1996.

108. De Caterina, R. and Libby, P., Control of endothelial leukocyte adhesion molecules
by fatty acids, Lipids, 31(suppl), 57, 1996.

109. Robinson, D.R., et al., Dietary marine lipids suppress the continuous expression of
interleukin-1B gene transcription, Lipids, 31(suppl):23, 1996.

110. Kaminski, W.E., et al., Dietary omega-3 fatty acids lower levels of platelet-derived
growth factor mRNA in human mononuclear cells, Blood, 81, 1871, 1993.

111. Holian, O. and Nelson, R., Action of long-chain fatty acids on protein kinase C
activity: comparison of omega-6 and omega-3 fatty acids, Anticancer Res., 12, 975,
1992.

112. Lucas, A., et al., Breast milk and subsequent intelligence quotient in children born
premature, Lancet, 339, 261, 1992.

113. Eurocat Working Group, Prevalence of neural tube defects in 20 regions of Europe
and the impact of prenatal diagnosis 1980–86. J. Epidemiol. Community Health, 45,
52, 1991.

114. Dwyer, J.H., et al., Arachidonate 5-lipoxygenase promoter genotype, dietary arachidonic
acid, and atherosclerosis, N. Engl. J. Med., 350, 29, 2004.

[datBtrue]

Source: Novel food ingredients for weight control,
C.J.K. Henry (Editor),
CRC; 1 edition (May 11, 2007)
pp 281-304

Omega-3 Fatty Acids and Other Polyunsaturated Fatty Acids and Weight Control
M. Sörhede Winzell and B. Ahrén, Lund University, Sweden

13.1 Introduction

Over the past decades, clinical investigations have evaluated the effects of polyunsaturated fatty acids (PUFAs), with particular interest in the omega-3 (or n-3) PUFAs, and their potential role in preventing metabolic diseases (Simopoulos, 1999, Manco et al., 2004, Riccardi et al., 2004, Nettleton and Katz, 2005). Over the past century, there has been a shift in the type of fat being consumed and today diets contain large amounts of saturated fat, high levels of omega-6 (or n-6) PUFAs and trans-fatty acids. The ratio between omega-6 and omega-3 PUFAs has increased tremendously due to decreased fish consumption in combination with increased intake of omega-6 PUFAs, owing mainly to the use of vegetable oils in cooking.

High intake of dietary fats, in particular saturated fats, may lead to the development of obesity, insulin resistance and type 2 diabetes (Arner et al., 1991; Taniguchi et al., 1992; Shulman, 2000; Zraika et al., 2002). This seems to be closely connected to the accumulation of triglycerides in non-adipocytes - including hepatocytes, myocytes and pancreatic B-cells - a phenomenon that has been called lipotoxicity (Zhou et al., 2000; Unger, 2003). Lipotoxicity is associated with increased endogenous glucose production from the liver, impaired insulin-stimulated glucose uptake in skeletal muscle and blunted glucose-stimulated insulin secretion from pancreatic cells (Unger and Orci, 2000, Unger and Zhou, 2001). The PUFAs may, however, exert different effects on metabolism, for example: (1) regulating fuel partitioning within the cell by stimulating oxidation and inhibiting lipogenesis; (2) altering membrane stability and fluidity and thereby affecting insulin signalling; (3) regulating gene transcription mainly via fatty acid regulated transcription factors such as the peroxisomal proliferator- activated receptors (PPARs) and the sterol regulatory element binding protein-1 (SREBP-1) (Clarke and Jump, 1994; Krey et al., 1997; Nakatani et al., 2003; Sampath and Ntambi, 2004). PUFAs may therefore have the capacity to prevent or counteract the detrimental effects of high-fat diets on body weight and whole-body metabolism.

It is important to determine optimal doses of PUFAs for prevention and treatment of metabolic diseases including overweight and obesity. This chapter will focus on the effect of various PUFAs, in particular the omega-3 PUFAs, on the control of body weight and whether dietary supplementation with these fatty acids may improve insulin resistance and type 2 diabetes.

13.2 Determining the role of omega-3 fatty acids and other polyunsaturated fatty acids in weight control

The positive effects of omega-3 PUFAs were observed early on among Greenland Inuits, who, despite high fat intake, displayed low mortality from coronary heart disease (Dyerberg et al., 1975). Other epidemiological studies have reported lower prevalence of obesity, type 2 diabetes and cardiovascular diseases in populations consuming large amounts of omega-3 PUFAs from fatty fish (Mouratoff et al., 1969; Kromann and Green, 1980). Subsequent studies have demonstrated that dietary supplementation of omega-3 PUFAs exerts positive effects in several metabolic diseases including coronary heart disease, hypertension, arteriosclerosis, diabetes and inflammatory diseases (Terry et al., 2003; Din et al., 2004; Calder, 2004; Ruxton et al., 2004).

13.2.1 Definition, structure and metabolism The PUFAs are fatty acids containing two or more double bonds.

These fatty acids are essential since they cannot be produced in the human body and must therefore be provided in the diet. There are two main types of PUFA, the omega-3 and the omega-6 fatty acids. In the omega-3 PUFAs, the first double bond is located between the third and the fourth carbons, counting from the methyl end of the carbon chain; in the omega-6 PUFA the double bond is located between the sixth and the seventh carbons (Fig. 13.1). Animals cannot, in general, produce omega-3 or omega-6 fatty acids since they lack the enzymes needed for insertion of the double bonds, whereas in plants these fatty acids are produced via 12- and 15- desaturase activity. The simplest members of the omega-6 and omega-3 fatty acids are linoleic acid (18:2n-6) and a-linolenic acid (18:3n-3), respectively (Fig. 13.1). Although mammalian cells do not synthesise linoleic acid and a-linolenic acid, these fatty acids are metabolised by desaturation and elongation reactions (Fig. 13.2). Linoleic acid is converted into y-linolenic acid (18:3n-6), which in turn can be elongated to produce arachidonic acid (20:4n-6) (Fig. 13.2). The same group of enzymes have the ability to metabolise a-linolenic acid and convert it into eicosapentaenoic acid (EPA; 20:5n-3). There is thus a competition between the omega-6 and the omega-3 fatty acids in the enzymatic reactions and also for their metabolisation. The 6-desaturase reaction is the rate-limiting step, and this enzyme has a-linolenic acid as its preferred substrate. In the next reaction step, EPA can be further converted through elongation to docosahexaenoic acid (DHA; 22:6n-3) (Fig. 13.2). These long-chain, more unsaturated forms of linoleic acid and a-linolenic acid are in turn substrates for the production of important biological molecules, which will be discussed later in this chapter.

13.2.2 Dietary sources

The different forms of the PUFAs are found in different food sources (Table 13.1). Plant seed oils like corn oil, sunflower oil and safflower oil are rich in omega-6 PUFAs, constituting up to 75% of the fatty acid content. Most plant oils are richer in omega-6 PUFAs than in omega-3 PUFAs (Table 13.2). Sunflower and safflower oil exist in two different forms, one rich in monounsaturated fat and one rich in PUFAs. Linoleic sunflower oil is available as liquid oil and it is also used in margarine. Because of the high levels of PUFAs in these oils, they are susceptible to oxidation during commercial usage, especially frying, and so they are hydrogenated to a more stable form. Thus, important dietary sources of omega-6 PUFAs are the vegetable oils and margarines. Green plant tissues are rich in a-linolenic acid (18:3n-3), constituting more than 50% of the fatty acids. This is, however, not a significant source of omega-3 PUFAs since the total fat content is very low (Table 13.3). a-Linolenic acid is abundant in plant oils derived from flaxseed, soybean and rapeseed (Table 13.2). The longer forms of omega-3 PUFAs are more readily found in fatty fish like salmon, herring and mackerel, but also are also found in lean fish liver – which contains large amounts of EPA and DHA (Table 13.3). Nuts contain considerable amounts of omega-3 PUFAs and walnuts, in particular, are rich in a-linolenic acid (Feldman, 2002).



The composition of dietary fatty acids has changed over the last 100 years (Simopoulos, 1995). The total intake of fat and the amount of saturated fats have increased as well as the omega-6 PUFAs, while the intake of omega-3 PUFAs has decreased. Studies in Palaeolithic nutrition suggest that the hunter–gatherer populations consumed equal amounts of omega-6 and omega-3 PUFAs (Eaton et al., 1998). Today the ratio between these fatty acids is 10–20:1 in the Western diet (Simopoulos, 1999). The reason for the decreased intake of omega-3 PUFAs is mainly a reduced intake of fish. In fact, modern agriculture results in decreased omega-3 PUFA content in many foods – including vegetables, meats, eggs and even in cultured fish – due to the industrial production of animal feed with high contents of omega-6-rich grains (Crawford, 1968, Simopoulos, 1999). The increased amount of omega-6 compared with omega-3 PUFAs in standard diets may have profound effects on human health since studies have indicated that omega-6 PUFAs may shift the physiological status into a prothrombotic, proaggregatory status with increased vasoconstriction and decreased bleeding time (Calder, 2005). The omega-3 PUFAs on the other hand seem anti-inflammatory, antithrombotic and hypolipidaemic, and may thus have beneficial effects in the prevention and/or treatment of several metabolic diseases (Calder, 2005).



The dietary PUFA intake is rather similar throughout Western societies. In Sweden and Finland the PUFAs represent around 5% of the total energy consumption (Becker, 1999, Valsta, 1999) and in the United States the intake averages 7%. The omega-3 PUFAs represent ~0.7% of the energy intake, mainly deriving from intake of vegetable oils. The ratio of omega-6 and omega-3 fatty acids is thus approximately 10:1 (Kris-Etherton et al., 2000). The dietary sources of PUFAs are mainly vegetable oils and linoleic acid is the major form, constituting 84–89%, while around 10% are represented by a-linolenic acid. The intake of highly unsaturated PUFAs, like the EPA and DHA found in fatty fish, is low, being 0.1–0.65 g/day in the United States. In the United Kingdom the pattern is similar with increasing consumption of linoleic acid (omega-6) and an estimated omega-3 intake of 0.1–0.5 g/day (Sanders, 2000). However, in Malaysian adults the eating pattern is different. The total fat intake range is 22–26%, while in Western countries it is 35–40%, and the PUFAs constitute only around 4% of the fats. The PUFAs consumed are mainly omega-6 linoleic acid and the omega-6: omega-3 ratio is approximately 10, similar to that in Europe and the United States (Tkw, 1997).

13.2.3 Food intake and body weight control

High-fat food intake is considered to be one of the major causes of the development of obesity and obesity-associated insulin resistance (Astrup, 2001; Riccardi et al., 2004). Laboratory animal studies and epidemiological studies in humans have demonstrated that consumption of high-fat dense diets, a typically Western diet, results in insulin resistance and obesity (Storlien et al., 2000; Astrup, 2001; Winzell and Ahren, 2004). There are however, studies indicating that different types of fat have different effects on whole-body energy metabolism and glucose homeostasis, and inclusion of dietary oils containing PUFAs have been proposed to exert positive effects both in patients and in animal models of type 2 diabetes (Malasanos and Stacpoole, 1991; Storlien et al., 1991). There are studies demonstrating that PUFAs, in particular the omega-3 PUFAs (EPA and DHA), are less effective in promoting obesity compared with saturated fats (Shillabeer and Lau, 1994; Azain, 2004). The mechanisms behind these observations probably involve modulation of fuel partitioning since PUFAs down-regulate lipogenesis and stimulate fat oxidation, because these fatty acids regulate the expression of several genes involved in lipid metabolism (Clarke, 2004; Sampath and Ntambi, 2004). Reduction in body fat content has been observed in rodents fed a diet containing fish oil (Ruzickova et al., 2004; Ikemoto et al., 1996), demonstrating that omega-3 PUFAs decreased the visceral fat by inhibiting both hypertrophy and hyperplasia of the fat cells.

In contrast, the effect of omega-3 PUFA on human body weight control is rather limited. However, in a recent study, overweight men and women were assigned to a daily fish meal, a weight-loss programme or the two in combination for 16 weeks and the effects on body weight and the plasma glucose and lipid profile were investigated (Mori et al., 1999). The fish meal did not in itself reduce the body weight of these obese subjects, but the dietary fish component significantly improved the outcome of the weight-loss programme in that body weight was reduced in combination with improved glucose and insulin levels as well as the serum lipid profile. In another study, 17 subjects (healthy, obese and type 2 diabetic) entered a 5-week diet programme with diets rich in either saturated fats or PUFAs (Summers et al., 2002). Both energy and fat intake appeared to be reduced in the subjects on the PUFA-rich diets, although body weight was not altered. The abdominal subcutaneous fat area was reduced in the group consuming the PUFA-rich diet, and this coincided with improved insulin sensitivity. The results indicate that PUFAs are effective in altering body fat content, which may have beneficial effects on energy metabolism.

13.2.4 Clinical studies on the effect of polyunsaturated fatty acids on glucose control and dyslipidaemia

The effect of omega-3 fatty acids on glycaemic control in humans is controversial. Several studies and reviews have indicated that omega-3 PUFAs have adverse effects in that these fatty acids induce elevated basal plasma glucose, and this was particularly pronounced in patients with type 2 diabetes consuming large amounts of fish oil (>10 g fish oil/day) (Borkman et al., 1989; Friday et al., 1989; Vessby, 1989). However, in other studies with lower doses of omega-3 PUFAs, ranging from 1–2 g/day, glucose homeostasis was maintained within normal ranges (Westerveld et al., 1993; Luo et al., 1998; Sirtori et al., 1998). Luo et al. (1998) demonstrated that a moderate intake of omega-3 PUFAs (1.8 g/day) in type 2 diabetic men resulted in a significant reduction in plasma triglyceride levels. There were, however, no effects on fasting glycaemia or HbA1c. During the 2-month study, body weight and energy intake remained stable. In addition, in other studies, which included patients with hypertension and dyslipidaemia, no adverse effects on plasma glucose levels were observed (Grundt et al., 1995; Toft et al., 1995). In both human and animal studies, dietary omega-3 PUFA supplementation was found to result in reduced circulating triglyceride levels, which may be one explanation for the improved insulin sensitivity observed after fish-oil feeding (Mori et al., 1999; Sirtori et al., 1998). The triglyceride-lowering effect is the most consistent and reproducible finding in both animal and human studies with omega-3 PUFAs and fish oil. Two meta-analyses of trials with omega-3 PUFAs or fish oil in patients with type 1 and type 2 diabetics, as well as in healthy controls, demonstrated that dietary fish oils have no statistically significant effect on glycaemic control but the supplementation efficiently reduced plasma triglyceride levels (Friedberg et al., 1998; Montori et al., 2000). There is thus strong evidence suggesting no adverse effects of fish oil or omega-3 PUFAs on glycaemia, and beneficial effects on plasma lipids, when consumed in moderate doses (1–3 g/day).

Animal studies have demonstrated that various dietary fat subtypes can modulate insulin action indicating that PUFAs have positive effects on insulin sensitivity (Storlien et al., 1991, 2000). One study, where rats were fed isocaloric high-fat diets with different types of fatty acids, demonstrated that diets rich in saturated fat resulted in insulin resistance while rats fed a high level of PUFAs with a low omega-6: omega-3 ratio had normal insulin action (Storlien et al., 1991). It is thus possible that saturated fatty acids affect the cellular membranes in a negative way resulting in impaired insulin action and that this can be prevented by the addition of unsaturated fatty acids to the diet (Ma et al., 2004). PUFAs may thus, at least in animal models, affect glycaemic control by improving insulin sensitivity.

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