One of the most interesting relationships between diet and vascular disease is the effect of omega-3 fatty acids on atherosclerosis. It was observed many years ago that Eskimos have a very low incidence of atherosclerosis, despite the fact that their traditional diet is extremely high in fats and devoid of fruits and vegetables. They also do not suffer from autoimmune diseases, such as rheumatoid arthritis and lupus. However, when they adopt a typical Western diet, they develop all of the diseases we do, and at the same statistical rate within the population.
Omega-3 fatty acids in the Eskimo diet come mainly from fish and whale blubber, and studies on this form of fat have indicated several remarkable properties: it is a mild blood anticoagulant, reduces inflammation by changing eicosanoid balance, and alters immunity, all things that potentially could reduce atherosclerosis. This finding led researchers and clinicians to test the results of adding omega-3 fatty acids to the diets of other populations. They found that omega-3 fatty acids eventually replaced the bad fats in cells and tissues of test subjects.
Some early studies seemed to indicate omega-3 fatty acids had a protective effect against heart attacks and strokes, but different studies produced conflicting results. Some demonstrated a dramatic reduction in heart attacks and strokes, others a minor effect, and some no effect at all. One of the problems with the negative studies was that olive oil was used as a control. Even at that time, it was known that olive oil has slight anticoagulant properties. Thus the control was not a placebo control at all: it is physiologically active, as are many such placebos.
One extremely large study involving 22,070 male physicians between the ages of forty and eighty-four years of age found that eating one fish per week reduced the incidence of sudden cardiac death by 52 percent.305 This is a dramatic reduction when you consider 250,000 people die of a sudden cardiac arrest every year, and that 55 percent of those people have had no previous history of heart disease. Most will die before reaching the hospital, and the survival rate is a dismal 30 percent for those who do make it to a hospital alive.
Interestingly, researchers found that the number of heart attacks was not reduced among test participants who consumed fish, but the incidence of sudden death associated with the event was lowered dramatically. They hypothesized that sudden death was caused by arrhythmia, which is powerfully inhibited by omega-3 fatty acids even at low concentrations.306 But some scientists have questioned the hypothesis that the main benefit provided by omega-3 fatty acids is related to arrhythmia reduction: in the study, the men who experienced the greatest benefits from increased omega-3 consumption also had the highest pre-existing incidences of hypertension, higher cholesterol levels, and a family history of heart disease. In other words, since they were already at significantly greater risk of coronary heart disease, the individual benefit was statistically greater than that reflected in the reported results.
Another stronger bit of information supporting the broader benefits of omega-3 fatty acid consumption comes from the Western Electric Study, which looked at the relation between fish consumption and coronary heart deaths among 1,822 men followed for thirty years.307 This study looked at heart failure, rather than sudden death, and found that participants with the highest fish consumption were the least likely to suffer coronary heart failure.
Analysis of the effects of consuming large amounts of omega-3 fatty acids in persons with high triglyceride levels demonstrates that the fish oils can significantly lower these levels, as well as significantly improve blood flow (by reducing blood viscosity) and raising HDL
A more recent analysis demonstrated that the two components of fish oils, EPA (eicosapen-taenoic acid) and DHA (docosahexaenoic acid), have important differential effects.309 While this study found no difference in the respective capacities of the two fatty acid components to lower total cholesterol, only DHA was shown to raise a particular type of HDL cholesterol—a subfraction called HDL2—which is protective against atherosclerotic vascular disease. In fact, DHA consumption increased HDL2 levels by 29 percent.
DHA also increased the levels of the larger LDL particle. This is important because recent studies have found that the size of the LDL particle is very important in atherosclerosis. Small LDL particles increase atherosclerosis and large ones may actually be protective. Unfortunately, doctors rarely order the test that differentiates the two forms of LDL cholesterol.
Other important differences were discovered over the course of the study. For example, one of the drawbacks of high omega-3 fatty acid intake is its effect on glucose tolerance, especially in type II diabetes. Some studies have shown that high intake of fish oils can impair glucose control, worsening this form of diabetes. This study has shown the effect occurs only with EPA, and not DHA. Interestingly, even with EPA, this negative effect on glucose control can be avoided by moderate exercise. I should emphasize that EPA does not cause problems with glucose control in normal individuals, only type II diabetics.
There is also some evidence that EPA reduces platelet adhesiveness, which is advantageous since platelet clumping is linked to an increased risk of sudden heart attack or stroke. Still, I recommend patients supplement their diets either with DHA only or with low EPA/DHA fish oils. This is because the Western Electric Study cited above also demonstrated that about 9 percent of DHA is metabolized back to EPA in amounts normally found in the body, providing exactly the right balance of EPA's clot-inhibiting effects. Therefore, DHA alone has all the properties that we desire from omega-3 fatty acids, such as beneficial anti-inflammatory, immune-modulating, antidepressant, and anticancer effects, as well as brain protection.
After reviewing the scientific literature, I think DHA-supplementation is an acceptable practice, and a safer alternative to food-source omega-3 fatty acids. Vegetarians will certainly appreciate this fact since DHA is derived from an algae, and not from fish. In fact, fish get their DHA from algae.
Some studies have shown that flaxseed oil provides the same benefits as fish oils.310 But, while some people, especially young healthy individuals, may derive the same benefits from either source, this is not true for everyone. Because flaxseed oil is high in alpha-linolenic acid, a fatty-acid precursor of EPA and DHA, it must first be converted to omega-3 fatty acid by the enzyme, delta-6 desaturase, which is naturally deficient in the very young, in the elderly, and in those with chronic illnesses. EPA has also been shown to interfere with delta-6 desaturase's ability to convert alpha-linolenic acid to omega-3.
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