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Coronary Heart Disease and Vegetarian Diet

B.k. Goyal

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'Heart attacks', which have become so common, occur due to involvement of coronary arteries, which carry the blood supply to the heart. An 'attack' results when one of the coronary arteries suddenly gets blocked and causes death of the muscle tissue of the heart supplied by that artery. This is clinically known as an 'attack' of myocardial infarction.

Why do coronary arteries get blocked ? There are two reasons which have been detected on post-mortem examination:

I. Blockage due to gradual narrowing of these arteries as a result of a degenerative disease known as atherosclerosis. Even as early as fifty to sixty years ago this atheroma was seen only in old people and was synonymous with the aging process. As the civilization has progressed, the time has come when the postmortems done on young children and young adults who have died due to accidents or other causes, have been showing atherosclerosis of the coronary arteries. Smoking, presence of long standing diabetes and high blood pressure, overweight and sedentary life are some of the known causes. However, the most important single biochemical abnormality which can be spotted and correlated with atheroma is the level of blood cholesterol. In the last few years the whole family of blood lipids has come to light. This consists of triglycerides, HDL and LDL cholesterol and a variety of apolipoproteins. It has been found that if the diet is rich in saturated fatty acids as in the case of non-vegetarian diets, the blood fat levels become highly abnormal and the process of atherosclerosis starts right from childhood. So striking was this association, that ten years back in the Western countries, the public was warned through the television and radio media, that their children should not be given more than two eggs per week. In fact such sensational discoveries have led many people in the West to take to vegetarianism.

Vegetarians have low intakes of total fat, saturated fatty acids and cholesterol. Their intake of polyunsaturates is equal or slightly higher and dietary fibre intake is usually much higher than w that of nonvegetarians. Some evidence exists that protein or dietary fibre in vegetarians may be involved in reducing coronary heart disease. The type and amount of dietary fat and cholesterol are most strongly associated with changes in serum lipids, apolipoproteins and blood rheology, all of which are the causes of coronary heart disease and heart attacks and are discussed below:

Blood Lipids (Fat)

Cholesterol circulates in the blood in two forms. The high density lipoprotein (HDL) cholesterol is protective for the heart and reduces the risk of coronary artery disease. As against this the low density lipoprotein (LDL) cholesterol increases the risk of coronary artery disease. The blood cholesterol levels are affected by the type of dietary fat and the amount of cholesterol present in it, alcohol, smoking and physical activity. The consumption of high saturated fatty acids (as in ghee and coconut oil) and cholesterol increases the LDL cholesterol levels. On the other hand the consumption of polyunsaturated fatty acids lower the levels of LDL cholesterol and not only that, they also increase HDL cholesterol levels thereby protecting the patients from coronary artery disease.

Apo-lipoprotein Levels

Apo-lipoprotein levels may be better than serum lipid levels for predicting the risk of coronary heart disease. Table 1 shows that in most but not in all studies, lipid-modified vegetarian diets were found to change levels of apolipoprotein as well as lipoprotein composition and levels.

II. The second reason for sudden blocking of the coronary arteries is the occurrence of a blood clot in an otherwise clean blood vessel. This type of blockage is specially seen in young people dying of heart attacks. Although there are a number of constituents in the blood responsible for this clotting, the role of platelets in blood seems to be outstanding.

Table I

Studies of Vegetarians and Coronar y Artery Disease

Outcome Vanable Study or Observations
Mortality from coronary artery disease Negative association between vegetarianism and ischemic heart disease mortality, even after removing confounding effects of smoking, especially in males.
35-64-y-old Seventh-day Adventist vegetarian men had lower mortality than did nonvegetarians although in men over 65 and women differences were significant, even after taking smoking into account.
Serum cholesterol levels: comparisons of vegetarians and nonvegetarians Total serum cholesterol, low-density-lipoprotein cholesterol, and to a lesser extent high-density-lipoprotein cholesterols are lower in vegetarians and especially vegans compared with lactovegetarians or omnivores.
Vegetarian diets usually produce a selective lowering of LDL levels, with lowered total cholesterol: LDL or LDL:HDL ratios.
Serum cholesterol levels Groups such as Macrobiotics and Hare Krishnas with members eating vegan or very restrictive vegetarian diets low in fat, high in polyunsaturated: saturated fatty acid ratios, high in dietaty fiber, and low in cholesterol show decreased total cholesterol and LDL cholesterol than do omnivores.
Vegetarians' LDL cholesterol levels are usually decreased but HDL cholesterol levels vary, some being higher than those of nonvegetarians, some lower.
Serum cholesterol levels: feeding vegetarians animal foods Feeding vegetarians beef, which is high in total fat and saturated fatty acids and cholesterol, causes 19% increases in total plasma cholesterol because of increase in LDL cholesterol whereas HDL cholesterol levels stay constant over a 2-wk period
Feeding lactovegetarians eggs for 3 wks, which increases dietary cholesterol, increases total and plasma cholesterol.
Serum cholesterol levels: feeding vegetarians animal foods Decreasing the amount and altering type of fat in Seventh-day Adventist vegetarians' diets further decreases serum lipid levels.
Serum cholesterol levels: feeding nonvegetarians vegetarian diets Nonvegetarians have decreased total cholesterol and LDL and HDL cholesterols when they are fed vegetarian diets low in total fat, saturated fatty acids, cholesterol protein, and high polyunsaturated fatty acids, P: S ratios carbohydrate, and dietary fiber for several months, Decreases are only one-third of those observed in lifelong vegetarlans.
Normolipidemic nonvegetarians fed a low-fat, semivegetarian diet for 3 mo have decreased total cholesterol, LDL cholesterol, and LDL: HDL ratios whereas HDL levels, weights, and plasma triglycerides stay constant.
Apoprotein levels Nonvegetarians fed vegetarian diets exhibit declines in apoprotein Al levels when diet is low in total fat, saturated fatty acids, and cholesterol and moderate in polyunsaturates .
Vegetarians on low fat, total fat, and saturated fatty acid diets show decreased apoprotein AI and B levels and elevated HDL cholesterol apoprotein Al and HDL: LDL cholesterol ratios increased.
Addition of eggs high in cholesterol to the diet of lactovegetarians increases apolipoprotein B levels in 3 wk.
Lactovegetarian diets fed to nonvegetarians for 6 wk led to no changes in apoprotein B levels although apoprotein B: total cholesterol and apoprotein B:LDL cholesterol ratios increased.
Platelet levels Lactovegetarians have altered platelet linoleic and arachidonic acid concentrations in comparison with nonvegetarians. Vegans and vegetarians do not differ in serum thromboxane or prostacyclin levels or platelet aggregation .
Nonvegetarians show changes in platelet function when saturated fatty acids are decreased and P: S ratios are increased platelet aggregation to thromboxane and clot ting activity of platelets is decreased and response to adenosine diphosphate aggregation is enhanced.
Saturated fatty acids increase thrombin aggregation and platelet function can be decreased by altering diets.

Platelets are important in clotting and in the development of the arterial thrombi that underlie most 'heart attacks' due to acute myocardial infarctions. They may also modulate coronary artery disease independently of factors such as smoking, blood pressure and genetics. Platelet composition and functional changes can be induced by dietary fat modifications. Saturated fatty acids are most highly associated with the changes in platelet aggregation to thrombin and platelet clotting activity. One of the theories is that, by decreasing saturated fatty acids as in the vegetarian diet, platelet aggregation and blood clotting changes predisposing to thrombosis will decrease.

Also clotting of a blood vessel depends on the blood fluidity known as "Blood Rheology". Possibly vegetarians have a better than average blood fluidity and this puts them at a lower risk of suffering coronary artery disease.

Finally in vegetarians, factors other than the diet may also be involved in lowering the risk of heart disease. These include i) the nonsmoking and the non-alcoholic status of vegetarians, which may affect HDL-cholesterol levels, ii) their physically active lives, which may favourably alter apo-lipoproteins as well as HDL cholesterol, iii) their relatively low weights, which may decrease risks of hypertension and non-insulin dependent diabetes.

It is also worth noting that the reduction in risks of coronary heart disease seem to be associated with the type of vegetarian diet that is followed rather than some genetic protective effect of vegetarianism per se.

The fact that mortality and morbidity from coronary artery disease is lower in vegetarians than in non-vegetarians has also been confirmed at the Bombay Hospital.

Although this hospital caters to all the communities the patients are strictly provided with vegetarian diet only. The studies are in progress at the Bombay Hospital Institute of Medical Sciences to go into the dietary causes of coronary artery disease and our initial data from these studies shows that out of the last hundred coronary heart disease patients, only thirty six patients were vegetarians.

Are there any special substances in the vegetarian diet which give protection against coronary heart disease? In India a lot of work has already been done on the role of garlic and onion in lowering blood cholesterol. Maize bran has also been shown to have a protective effect on the cardiovascular status. Many other vegetarian foods, protective to the heart, have been discussed in another chapter.

Hence it seems evident, that vegetarianism offers definite protection from coronary heart disease.

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