| '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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