The medical literature emphasises plaque formation as the major factor affecting arterial blood flow. However, many acute myocardial infarctions are the result of plaque rupture and subsequent thrombus formation.32 Factors that deter thrombus formation and platelet aggregation may improve the clinical prognosis substantially. Alcohol has been found to decrease platelet aggregation. Garlic and n-3 (omega-3) fatty acids can also decrease platelet aggregation and increase fibrinolytic activity.11,21 Saturated fatty acids and polyunsaturated fatty acids increase platelet aggregation.15,21 A P/S ratio (defined as the ratio of polyunsaturated fatty acids to saturated fatty acids) greater than 0.8 is associated with increased platelet aggregation.15,21 Hence, substituting polyunsaturated fat for saturated fat reduces LDL cholesterol levels but may increase thrombus formation.
N-3 Fatty Acids
At first glance, physicians might avoid technical information about n-3 fatty
acids because these compounds fall into complex biochemical pathways, but their
actions are fairly straightforward and important. Dietary n-3 fatty acids are
derived from plant and seafood sources. Plant sources provide a medium-chain
fatty acid of 18:3 n-3 (called alpha-linolenic acid). Seafood provides long-chain
fatty acids of 20:5 n-3 (called EPA or eicosapentaenoic acid) and 22:6 n-3 (called
DHA or docosahexaenoic acid). Alpha-linolenic acid is converted into long-chain
fatty acids. Since linoleic acid and linolenic acid compete for the same delta-6
desaturase enzyme reaction,33 this conversion accelerates greatly, increasing
EPA levels 2.5-fold, when linoleic acid (polyunsaturated fat) intake is limited.
Polyunsaturated fats (e.g., corn oil, peanut oil) inhibit the beneficial actions
of n-3 fatty acids
Plant Sources of n-3 Fatty Acids
Alpha-linolenic acid is an n-3 fatty acid found in green leafy vegetables, canola
oil, flax oil, soybean products, walnuts and hazelnuts.
Increased intake of foods rich in alpha-linolenic acid decreases LDL cholesterol
levels.34 Intake of linolenic acid is strongly associated with a decreased risk
of coronary artery disease.35 In one study35 of 43,757 health professionals,
the protective cardiac effect achieved with linolenic acid was more significant
than a reduction in saturated fat intake. Of particular interest in this study
was the finding that plant sources of n-3 fatty acids exhibited a significant
protective effect, while seafood sources of n-3 fatty acids did not. Similarly,
in the Mediterranean diet study, a threefold increase in alpha-linolenic acid
intake was a factor associated with a 70 percent reduction in mortality rates.
Seafood Sources of n-3 Fatty Acids
Fish and fish oils are other common dietary sources of n-3 fatty acids. Fish
oils decrease triglycerides36,37 and offer an alternative in the treatment of
hypertriglyceridemia to gemfibrozil (Lopid), which may be contra-indicated in
many patients. Unfortunately, the long-term safety of fish oil as an agent to
reduce triglyceride levels remains unknown. Long-chain n-3 fatty acids also
decrease platelet aggregation and improve blood viscosity.36,37 Fish oils, in
a dosage of 10 g per day, have almost the same platelet effect as 325 mg of
aspirin daily. Studies evaluating fish consumption and rates of coronary artery
disease in healthy adults have provided conflicting results.38,39 There is currently
no solid evidence that people without coronary artery disease should eat more
seafood. However, studies in patients with coronary artery disease have been
more promising, demonstrating significant reductions in mortality and infarction
rates.40 The clinical benefits of eating one to two servings of seafood weekly
might result from reduced platelet aggregation in people with significant arterial
narrowings. Anti-arrhythmic activity associated with increased fish consumption
has also been hypothesized as the cause of decreased mortality rates in patients
with known coronary artery disease.
Dietary changes can help prevent and treat coronary artery disease. Some diets, like the Mediterranean and Japanese diets, are associated with much lower rates of coronary artery disease than the traditional Western diet. The former diets limit the intake of saturated and polyunsaturated fats and supply an abundance of dietary antioxidants and alpha-linolenic acid. Further evidence that a Japanese or Mediterranean diet is in itself beneficial is the finding that Americans have a higher rate of cardiac mortality even when their cholesterol levels are the same as the levels of Japanese or Southern Europeans41 (Figure 4). Nondietary lifestyle factors, such as increased activity, may also influence differences in mortality rates. Physicians can sweeten dietary recommendations to their patients by emphasising the addition of specific beneficial foods, rather than the elimination of foods. Soy products, legumes, garlic, soluble fibre and nuts rich in monounsaturated fat all reduce serum LDL cholesterol levels and should be encouraged as daily staples in the Western diet. Dietary antioxidants hinder arterial plaque formation and improve endothelial vasomotor function. In particular, garlic, red grapes juice, monounsaturated fats, and fruits and vegetables are associated with decreased oxidation of LDL cholesterol. Physicians can encourage their patients to start improving their diets by adding specific beneficial foods, which may be easier than giving up unhealthy foods.
Intake of saturated fat increases the rates of strokes and heart attacks. Trans fatty acids act like saturated fats and are associated with worsened lipid profiles. Physicians should encourage patients to decrease their use of saturated fat and trans fatty acids
Moderate use of monounsaturated fats (canola oil and olive oil) decreases LDL cholesterol levels and LDL oxidation and appears preferable to use of highly polyunsaturated fats. In contrast to ultralow-fat diets, the "take home message" from clinical studies of a Mediterranean diet is that switching from saturated and polyunsaturated fats to monounsaturated and n-3 fats is more important than cutting the total fat intake.
Intake of n-3 fatty acids from plant and fish sources is associated with anti-arrhythmic activity, decreased platelet aggregation and decreased rates of sudden death in patients with known coronary artery disease. In repeated clinical trials, plant sources of alpha-linolenic acid have been associated with decreases in LDL cholesterol levels and decreases in the rate of morbidity and mortality associated with coronary artery disease. One to two servings of seafood a week appears to benefit patients with coronary artery disease. Healthy populations have not shown a consistent benefit from eating more seafood. Studies that assess intake of n-3 fatty acids from fish sources also need to assess the intake of n-3 fatty acids from plant sources.
Except for the Mediterranean diet study, we lack controlled, randomised clinical trials using dietary interventions to assess clinical outcomes. While the Ornish program excels at improving intermediate markers of coronary artery disease (i.e., LDL cholesterol levels and treadmill results), no randomised trials show that the Ornish program decreases cardiac mortality, overall mortality or even nonfatal cardiac events. And, while the Mediterranean diet showed a decrease in cardiac and noncardiac mortality and events in patients with coronary artery disease in France, and might be more easily accommodated by some patients than ultralow-fat diets, it remains to be proved that the Mediterranean diet is applicable to other countries and cultures.
A modified "antioxidant diet"(all yellow and orange coloured fruits and vegetables) that includes up to 20 percent of total calories from fat (largely monounsaturated fat and n-3 fatty acids) and generous amounts of dietary antioxidants from plant sources could increase patient compliance and might lead to a decrease in overall mortality and morbidity.
Physicians can motivate their patients to eat better by providing them with brief but detailed nutritional information. Short, repetitive messages regarding nutrition are effective in changing patients' eating habits.1 In patients with known coronary artery disease, LDL and TC/HDL target levels should be reached within two to six months of diet therapy, or lipid-lowering medications should be considered. Ongoing dietary intervention should continue even after lipid-lowering medications are initiated.