Essential fatty acids in health and chronic disease

Human beings evolved consuming a diet that contained about equal amounts of n-3 and n-6 essential fatty acids. Over the past 100-150 y there has been an enormous increase in the consumption of n-6 fatty acids due to the increased intake of vegetable oils from corn, sunflower seeds, safflower seeds, cottonseed, and soybeans. Today, in Western diets, the ratio of n-6 to n-3 fatty acids ranges from approximately 20-30:1 instead of the traditional range of 1-2:1. Studies indicate that a high intake of n-6 fatty acids shifts the physiologic state to one that is prothrombotic and proaggregatory, characterized by increases in blood viscosity, vasospasm, and vasoconstriction and decreases in bleeding time. n-3 Fatty acids, however, have antiinflammatory, antithrombotic, antiarrhythmic, hypolipidemic, and vasodilatory properties. These beneficial effects of n-3 fatty acids have been shown in the secondary prevention of coronary heart disease, hypertension, type 2 diabetes, and, in some patients with renal disease, rheumatoid arthritis, ulcerative colitis, Crohn disease, and chronic obstructive pulmonary disease. Most of the studies were carried out with fish oils [eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)]. However, alpha-linolenic acid, found in green leafy vegetables, flaxseed, rapeseed, and walnuts, desaturates and elongates in the human body to EPA and DHA and by itself may have beneficial effects in health and in the control of chronic diseases.

New products from the agri-food industry: the return of n-3 fatty acids into the food supply

The meat from animals and fish in the wild, chicken eggs produced under complete natural conditions, and wild plants contain higher amounts of n-3 fatty acids compared to domesticated or cultivated ones. The composition of meats, fish, and eggs is dependent on animal feed. Fish-meal, flax, and n-3 from algae in animal feeds increase the n-3 fatty acid content of egg yolks and lead to the availability of n-3 fatty acid-enriched eggs in the marketplace. Research is ongoing for the production of n-3 fatty acid-enriched products from poultry, beef, lamb, pork, milk, bakery products, etc. In the case of n-3 fatty acid-enriched eggs, the egg under complete natural conditions (Greek or Ampelistra egg) can serve as a guide for proper composition. Otherwise, the amount of n-3 fatty acids is determined by the organoleptic properties of the products. It is essential in the process of returning the n-3 fatty acids into the food supply that the balance of n-6/n-3 fatty acids in the diet that existed during evolution is maintained. Clinical investigations confirm the importance of n-3 fatty acids for normal function during growth and development and in the modulation of chronic diseases. The availability of n-3 fatty acid-enriched products should lead to improvements in the food supply. Pregnant and lactating women and infants should benefit since their diet is deficient in n-3 fatty acids, especially for the vegetarians among them. Studies with n-3-enriched eggs lower cholesterol levels, platelet aggregation, and blood pressure. Since cardiovascular disease, hypertension, and autoimmune, allergic, and neurological disorders appear to respond to n-3 fatty acid supplementation, a diet balanced in n-3 and n-6 fatty acids consistent with the diet during human evolution should decrease or delay their manifestation.

Evolutionary aspects of omega-3 fatty acids in the food supply

Information from archaeological findings and studies from modern day hunter-gatherers suggest that the Paleolithic diet is the diet we evolved on and for which our genetic profile was programmed. The Paleolithic diet is characterized by lower fat and lower saturated fat intake than Western diets; a balanced intake of omega-6 and omega-3 essential fatty acids; small amounts of trans fatty acids, contributing less than 2% of dietary energy; more green leafy vegetables and fruits providing higher levels of vitamin E and vitamin C and other antioxidants than today's diet and higher amounts of calcium and potassium but lower sodium intake. Studies on the traditional Greek diet (diet of Crete) indicate an omega-6/omega-3 ratio of about 1/1. The importance of a balanced ratio of omega-6:omega-3, a lower saturated fatty acid and lower total fat intake (30-33%), along with higher intakes of fruits and vegetables leading to increases in vitamin E and C, was tested in the Lyon Heart study. The Lyon study, based on a modified diet of Crete, confirmed the importance of omega-3 fatty acids from marine and terrestrial sources, and vitamin E and vitamin C, in the secondary prevention of coronary heart disease, and cancer mortality.

The nutritional aspects of hypertension

This article reports dramatic results achieved by the Dietary Approaches to Stop Hypertension (DASH) and other clinical trials and studies in lowering blood pressure in both hypertensives and normotensives, suggesting that it could be useful in both preventing and managing blood pressure.

Omega-3 fatty acids in the prevention-management of cardiovascular disease

Epidemiologic studies show that populations who eat fish versus those who do not have a reduced death rate from cardiovascular disease. Experimental studies have shown that omega-3 fatty acids affect the function of cells involved in atherothrombosis in numerous ways, including the modification of eicosanoid products in the cyclooxygenase and lipoxygenase pathways, the reduced synthesis of cytokines and platelet-derived growth factor, and alterations of leukocyte and endothelial cell properties. Intervention studies in patients with restenosis, myocardial infarction, and cardiac arrhythmias with omega-3 fatty acid supplementation have been addressed in several clinical studies. The ingestion of omega-3 fatty acids following one episode of myocardial infarction appears to decrease the rate of cardiac death. These effects of omega-3 fatty acids appear to be due to their antiarrhythmic properties. In fact, fish oil has been shown to reduce ventricular arrhythmias and to be more beneficial than currently used pharmacologic agents. The dose, duration, and mechanisms involved in the prevention and management of cardiovascular disease following omega-3 fatty acid ingestion or supplementation need to be investigated by double blind controlled clinical trials.

Genetic variation and nutrition

Advances in genetics and molecular biology indicate that susceptibility to chronic diseases such as coronary artery disease (CAD), hypertension, diabetes, obesity, osteoporosis, alcoholism, cancer, etc., to a great extent is genetically determined. Studies have shown that 50% of the variance in plasma cholesterol concentration is genetically determined, whereas 30%-60% of the variance in blood pressure is genetically determined. For fibrinogen, an independent risk factor for CAD, 15%-50% of the variance is genetically determined. In the U.K. population the variance for the fibrinogen level is 15% whereas in the Hawaiian population, the variance is 50%, indicating significant differences between populations. Among Australians, 75% of the variance in bone density is found to be genetically determined. Genetic variation influences the response to diet. For example, individuals with ApoE4 have higher cholesterol levels and a higher risk of CAD than those with ApoE3. Additional studies show that women of the ApoE 3/2 phenotype stand to benefit the least from a high polyunsaturate: saturate (P:S) diet because of reduction in the more 'protective' high density lipoprotein cholesterol (HDL-C), whereas men of the ApoE 4/3 phenotype showed the greatest improvement in the LDL/HDL ratio. Therefore a general recommendation to increase the polyunsaturated content of the diet in order to decrease the risk for CAD is not appropriate for women with ApoE 3/2 phenotype. Thus, specific information is needed to define the optimal diet for an individual.

The role of fatty acids in gene expression: health implications

The effect of nutrients on gene expression is an area of considerable interest as the number of genes coding for key regulatory proteins in metabolic pathways is investigated. This paper presents an overview of the role of omega-6 and omega-3 fatty acids on the expression of genes involved in lipogenesis, glycolysis, glucose transporters, inflammation, early gene expression, and vascular cell adhesion molecules. Whereas some of the transcriptional effects of omega-6 and omega-3 fatty acids appear to be mediated by eicosanoids, the suppression of lipogenic and glycolytic genes is independent of eicosanoid synthesis, and appears to involved a nuclear mechanism directly modified by these fatty acids.

Is insulin resistance influenced by dietary linoleic acid and trans fatty acids?

The incidence of obesity, noninsulin-dependent diabetes mellitus (NIDDM), hypertension, and coronary artery disease has increased in the developed world. At the same time, major changes in the type and amount of fatty acid intake have occurred over the past 40-50 years, reflected in increases in saturated fat (from both animal sources and hydrogenated vegetable sources), trans fatty acids, vegetable oils rich in linoleic acid, and an overall decrease in long chain polyunsaturated fatty acids (arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid--C20-C22). Recent findings that C20-C22 in muscle membrane phospholipids are inversely related to insulin resistance, whereas linoleic acid is positively related to insulin resistance, suggest that diet may influence the development of insulin resistance in obesity, insulin-dependent diabetes mellitus (IDDM), hypertension, and coronary artery disease (including asymptomatic atherosclerosis and microvascular angina). These conditions are known to have genetic determinants and have a common abnormality in smooth muscle response and insulin resistance. It is proposed that the current diet influences the expression of insulin resistance in those who are genetically predisposed. Therefore, clinical investigations are needed to evaluate if lowering or preventing insulin resistance through diet by increasing arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid, while lowering linoleic acid and decreasing trans fatty acids from the diet, will modify or prevent the development of these diseases.