Coronary Heart Disease: Nutritional Considerations

The role of diet in coronary heart disease is evident from its pathological process, which involves the formation of arterial plaques, alterations in endothelial function (which, in turn, influence blood pressure), heightened risk for thrombosis, and inflammatory processes. Diet plays a role through the regulation of blood lipids and by influencing endothelial function and the underlying inflammation that causes disease progression. A modified diet, particularly if combined with regular exercise, can prevent, delay, or reverse the progression of atherosclerosis and development of CHD, with subsequent reduction in cardiovascular events.

The primary goals of dietary intervention are described below.

Controlling Blood Lipid Concentrations

Saturated fats and cholesterol in the diet increase levels of blood lipids, particularly LDL cholesterol, while soluble fiber tends to reduce them. Controlling blood lipoprotein concentrations with a combination of diet, exercise, and medication, if necessary, is a cornerstone of treatment for most CHD patients, as described in more detail in the Hyperlipidemia chapter.

Decreasing dietary saturated fat and cholesterol. Following diets low in saturated fat and cholesterol can help reduce progression of atherosclerosis.¹³ The National Cholesterol Education Program has recommended moderate reductions in total fat (≤ 30% of energy), saturated fat (≤ 7% of energy), and cholesterol (< 200 mg/day) intake. In clinical trials, such changes reduce plasma LDL cholesterol concentration about 5%.¹⁴ Studies suggest that low–fat vegetarian and vegan regimens are significantly more effective, reducing LDL cholesterol approximately 15% to 30%.^15–16 Because such regimens have also been shown to reduce body weight and blood pressure and to be useful in programs for reversing atherosclerosis, they may be preferable to many patients, provided they are prescribed along with basic diet instruction.¹⁷

Increasing dietary fiber. Soluble fiber, as is found in oats, barley, and beans, is particularly helpful in this regard. (See Hyperlipidemia for more information.)Sources of soluble dietary fiber and pectin, found mainly in fruits and vegetables, have also reduced atherosclerotic progression.¹⁸

Consuming soy products. Both epidemiologic¹⁹ and clinical²⁰ studies have shown that soy foods (eg, soymilk and meat substitutes) may reduce CHD risk. In addition to reducing blood lipids, soy has cardioprotective effects, such as lowering oxidized LDL, homocysteine, and blood pressure.

Clinical trials have combined these lipid–lowering strategies. A vegetarian diet emphasizing cholesterol–lowering foods (including oats, soy foods, nuts, and sterol/stanol margarines) appears to be particularly effective, lowering LDL cholesterol concentration approximately 30%, an effect similar to that of treatment with lovastatin.²⁰

Improving Antioxidant Status and Endothelial Function
Dietary antioxidants, folate, magnesium, and other substances in foods may reduce the burden of oxidized LDL and improve endothelial function through increased availability of nitric oxide. Diet–related improvements in endothelial function may also reduce blood pressure.

Fruits and vegetables can help reduce atherosclerosis and lower risk for CHD, particularly if the diet is low in saturated fat.²¹ However, the benefits of these foods go beyond their having no cholesterol, very little saturated fat, and abundant fiber. Among their cardioactive components are vitamin C,²² antioxidant flavonoids,²³ and folic acid.²⁴

Several studies have shown that higher dietary intakes of carotenoid–containing fruits and vegetables are associated with a decreased risk of coronary artery disease.25 Others have found an inverse relationship between lower blood levels of carotenoids and higher risk for cardiovascular events.²⁶

Reducing Inflammation

The role of inflammatory processes in atherosclerosis is increasingly apparent. Loss of excess body fat reduces the inflammation that acts as both a promoter of atherosclerosis progression and a trigger for cardiovascular events. In addition, shifting the balance of dietary fat away from saturated fats toward omega–3 fatty acids appears to reduce atherosclerosis and may help lower coronary risk, presumably by reducing inflammatory processes. This balance can be altered by the elimination of animal products, tropical oils (the leading sources of saturated fats), and partially hydrogenated vegetable oils (trans fats).

Some investigators have further adjusted this balance in clinical studies by the addition of omega–3 fatty acids in either foods or supplements. And several researchers have found an anti–atherosclerotic effect from both alpha–linolenic acid²⁷ and long–chain omega–3 fats.²⁸ Cardioprotective properties of these fatty acids include reduction of blood viscosity and triglyceride–lowering, antiplatelet, antidysrhythmic, and anti–inflammatory effects.²⁹

There are 3 important caveats to such studies. First, benefits of omega–3 fatty acids have generally been demonstrated in individuals following less than optimal diets, rather than in vegetarians or individuals following very low–fat diets. Second, while many studies have used fish oils, some evidence indicates that diets rich in plant sources of omega–3 fatty acids are associated with a similar reduction in heart disease risk.³⁰ Walnuts, flaxseed, flaxseed oil, and canola oil are rich sources of alpha–linolenic acid and lack the cholesterol of nonplant sources of omega–3 fatty acids. Third, fats or oils that provide omega–3 fatty acids are as energy dense as any other fats and are mixtures of various fat types. Fish oils, for example, include significant amounts of saturated fat (15%–30% of total fat content) and cholesterol. Patients who include fatty fish in their diets as a means of increasing omega–3 intake will also increase total and saturated fat intake, and may experience elevated cholesterol and weight gain.

In addition to the above considerations, evidence suggests that other dietary factors may be helpful, as described below.

In epidemiological studies, whole grain consumption is associated with a lower risk of heart disease,³¹ as is frequent consumption of nuts.³² In addition to providing the lipid–lowering benefit of dietary fiber, these foods provide magnesium and vitamin E, both of which are inversely related to coronary heart disease occurrence or mortality.^33–34 Nuts are high in fat and calories, however, and may influence body weight.

The role of alcohol remains controversial. No controlled clinical trials have examined the effect of alcohol intake on cardiovascular endpoints. Nevertheless, moderate alcohol consumption (1–2 drinks/day) may reduce cardiovascular disease risk through several mechanisms: increasing blood concentrations of HDL cholesterol, plasminogen, and tissue plasminogen activator; improving endothelial function; and decreasing platelet aggregation, fibrinogen, and lipoprotein (a).³⁵ However, regular alcohol consumption also contributes to several medical conditions, including serious diseases of the liver, pancreas, central nervous system, and cardiovascular system. Alcohol also increases the risks for some cancers, notably gastrointestinal and breast cancers.³⁶

Control of Major CHD Risk Factors

Coronary heart disease risk is significantly influenced by the development of comorbid diet–related conditions, including abdominal obesity, high blood pressure, and elevated blood glucose concentrations. A combination of these conditions (along with elevated triglycerides and/or low HDL) is known as metabolic syndrome. The presence of metabolic syndrome predicts CHD more strongly than its individual components do.³⁷

Preventing excess weight gain can lower the risk for coronary artery disease. Accumulation of abdominal fat in particular is associated with the severity of coronary atherosclerosis.³⁸ Studies have shown that obesity is a predictor of acute coronary events.³⁹ Loss of excess body weight also reduces the inflammatory marker C–reactive protein and the proinflammatory cytokine interleukin 6, both of which have been correlated with CHD risk.^40,41

Blood pressure. Reductions in blood pressure to optimal levels prevent an estimated 37% of CHD events in men and 56% in women.⁴² (See Hypertension.)

Blood glucose concentrations. Chronically elevated blood glucose increases risk for coronary disease.⁴³ Even in persons without diabetes, impaired glucose tolerance is predictive of greater risk for cardiovascular morbidity,⁴⁴ and normalization of postprandial hyperglycemia reduces cardiovascular events in these patients.⁴⁵

Exercise. Regular exercise reduces cardiovascular mortality in patients with established coronary heart disease,⁴⁶ particularly if the activity is sufficiently intense.⁴⁷ Current recommendations suggest a minimum of 30 minutes of moderately vigorous physical activity every day. Before a CHD patient starts an exercise regimen, however, a physical examination is essential, with particular attention to cardiac function, joints, and feet.

Survival and Prognosis after Coronary Events

A low–fat vegetarian diet reduces the risk for repeated coronary events. Individuals who adhered to a low–fat (< 10% of energy) vegetarian diet as part of treatment for pre–existing heart disease had an absence of coronary events in a 12–year study.¹⁶ Diet interventions that have also included exercise, stress reduction, and smoking cessation appear to cause regression of atherosclerotic lesions.¹⁵

Mediterranean–style diets also decrease the risk for repeated cardiovascular events. The combination of known protective nutrients found in the plant based Mediterranean diet significantly reduced cardiac death, nonfatal MI, unstable angina, stroke, heart failure, and pulmonary or peripheral embolism when compared with a Western diet.48 However, Mediterranean diets are higher in fat (25%–35%) than low–fat vegetarian diets, and are therefore not likely to be as effective for weight loss or regression of atherosclerotic lesions.

Orders

Vegetarian diet, non–dairy, low–fat

Nutrition consultation to advise patient regarding the above diet and arrange follow–up.

Smoking cessation.

Exercise prescription: Patient must be screened to ensure safe initiation of an exercise program and slowly work toward a goal of 30 minutes daily of aerobic semivigorous activity. Exercise physiology and physical therapy consultation as appropriate.

What to Tell the Family

Atherosclerosis and coronary heart disease are preventable, treatable, and in some cases possibly reversible. Diet therapy and exercise are fundamental for these aims, and many patients are eventually able to reduce or eliminate previously required medications. Vegetarian diets are particularly effective and appear to be as acceptable to patients as other regimens. Because such diets usually require learning new cooking techniques and acquiring new tastes, families play an important role in joining the patient in the process of dietary change. Family members can support the heart disease patient by following a similar diet and exercise regimen, which will likely benefit their health as well.