Download Cardiac Diseases and the role of nutrition

Cardiac Diseases and the role of nutrition
A very large percentile of Indians dies of cardiovascular disease. The
morbidity and mortality associated with coronary artery disease is strongly
related to abnormal lipid levels, oxidation of lipids and intra-arterial clot
formation. Nutrition powerfully influences each of these factors. The cause
clearly lies in the eating habits, food choices and other lifestyle related
problems.
There is growing evidence that patients can improve lipid levels and
decrease the rate of cardiovascular events by ‘adding’ specific foods to their
diets and switching from saturated and polyunsaturated to
monounsaturated fats and n-3 fatty acids.
Appropriate dietary changes decrease arteriosclerotic plaque formation,
improve endothelial vasomotor dynamics, reduce oxidation of low-density
lipoproteins and enhance thrombolytic activity. Changes in diet can reduce
the premature mortality and morbidity associated with coronary artery
disease.
We lack controlled randomized clinical trials that clearly establish the ideal
LDL cholesterol level or total cholesterol/high-density lipoprotein
(TC/HDL) ratio. However, in patients with known coronary artery disease,
strong evidence based on clinical outcomes suggests that patients with high
LDL cholesterol levels can decrease their risk of mortality and morbidity by
reducing their LDL cholesterol level by 30 to 35 percent.
The Triglycerides divided by HDL should be <2.
Not all patients are willing or able to reach these lipid targets with lifestyle
changes alone. Patients at high risk of coronary artery disease who fail to
reach these targets with diet and exercise should be properly guided on the
dietary approach.
Dietary Recommendations for Improving Lipid Levels
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• Eat at least five to seven servings of vegetables and fruits daily.
• Eat soy products and legumes daily.
• Use oils that contain monounsaturated fatty acids and n-3 fatty acids
(such as canola and olive oil).
• Eat monounsaturated-rich nuts in moderation.
• Eat garlic regularly (if acceptable).
• Increase intake of soluble fiber.
• Decrease intake of saturated fat, polyunsaturated fat and transfatty
acids; in particular, follow these guidelines:
• Decrease consumption of butter and margarine.
• Decrease consumption of fatty meats.
• Decrease consumption of dairy products made from 2% or whole
milk
While clinicians often tell patients what to eliminate from their diets to
reach a more favorable lipid profile, they can enhance their advice by also
telling them what to add. Patients might perceive food additions as more
palatable than food restrictions.
Increase Soya Products and Legumes
Intake of soya products decreases LDL and total cholesterol levels without
decreasing HDL cholesterol levels. Legume intake has also been shown in
studies to decrease LDL and total cholesterol levels without decreasing
HDL levels. Soya and bean products can serve as a protein source in a meal
and can further reduce LDL cholesterol levels if they are substituted for
fatty animal products.
Increase Garlic
Several meta-analyses have shown that garlic intake reduces LDL
cholesterol levels by up to 9 percent and produces a small rise in HDL
cholesterol levels; one medium-size garlic clove daily is sufficient. Garlic
has no known side effects except for the presence of odor in some
individuals.
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So far, no clinical trials have proved that increased intake of garlic
decreases cardiac-induced mortality or morbidity, yet its use appears safe
and potentially beneficial.
Increase Soluble Fiber
Soluble fiber increases excretion of fecal bile acid and removal of
cholesterol. Good sources of soluble fiber include oat products, barley,
fruits and vegetables. Several studies have shown that one daily serving of
oat bran or oatmeal decreases total cholesterol levels by up to 3 percent.
Pectin, a soluble fiber found in fruit, also decreases LDL cholesterol levels.
Several servings must be eaten daily for substantial reductions. Exchanging
soluble fiber for fat intake produces even greater reduction in LDL
cholesterol levels.
Increase Monounsaturated Fats
Both monounsaturated and polyunsaturated fatty acids decrease LDL and
total cholesterol levels and produce a small increase in triglyceride levels.
However, there is growing evidence that increased intake of
polyunsaturated fatty acid increases the oxidation of LDL cholesterol,
leading to increased LDL uptake by macrophages, foam cell formation
within the arterial intima and development of coronary artery obstruction.
Polyunsaturated fatty acids also increase platelet aggregation, which can
increase thrombus formation and the risk of stroke and myocardial
infarction. These factors make the intake of monounsaturated fats
preferable to polyunsaturated fats.
In contrast to the dominant use of polyunsaturated fat sources in most of
the Western world, the Mediterranean diet uses predominantly
monounsaturated fatty acids and n-3 fatty acids (omega-3 fats) as fat
sources. To test the applicability of the Mediterranean diet in patients with
cardiac disease, investigators in France randomized 605 post myocardial
infarction patients to either a control diet similar to the (NCEP) Step I-II
diet (with 30 percent of total calories from fat) or an experimental diet
similar to the Cretan Mediterranean diet. The Cretan diet uses olive oil and
special canola-oil margarine as its fat source. In this study, the Cretan diet
also included more servings of legumes per day than the NCEP-like diet.
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Significant reductions in infarction, unstable angina, heart failure, and
stroke and thromboembolic events were noted in the patients on the
experimental diet.
Over five years, total mortality decreased by 70 percent in the patients who
followed the Mediterranean diet compared with the patients who followed
the control diet. Since the difference in fat intake was minimal (33 percent
in the control diet versus 30 percent in the Mediterranean diet) and lipid
profiles were analogous, factors other than a reduction in fat intake must
account for these striking differences in clinical events. These results are
important because they indicate that dietary changes, independent of lipid
levels, influence outcomes of patients with coronary heart disease.
Increase Monounsaturated-Rich Nuts
Nuts are a rich source of n-3 fatty acids, monounsaturated fats and vitamin
E. Studies have shown that an increased intake of nuts is associated with
improved lipid levels and decreased mortality and myocardial infarction.
Nuts rich in monounsaturated fats and n-3 fats (e.g., hazelnuts, almonds,
cashews, walnuts) appear preferable to nuts containing polyunsaturated
fats, such as peanuts.
Reduce Saturated Fats and Trans Fatty Acids
It is well established that reducing intake of saturated fat reduces LDL
cholesterol levels and that reductions in LDL cholesterol levels decrease
the risk of coronary artery disease. European studies have shown that the
causal relationship between saturated fat intake and coronary artery disease
may be stronger than the relationship between coronary artery disease and
hypertension, diabetes or tobacco use.
With the increasing popularity of margarine, trans fatty acids are gaining in
use and now represent 2 to 3 percent of total calories in the diet. Trans
fatty acids increase LDL cholesterol levels and decrease HDL cholesterol
levels. Studies have shown that people can reduce their intake of saturated
fat and trans fatty acids by nearly 50 percent by cutting out three dietary
sources: butter and margarine, fatty meats and dairy products made from 2
percent or whole milk.
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Methods of Decreasing Oxidation of LDL Cholesterol
A growing body of evidence suggests that the oxidation of cholesterol is an
important factor in the development of coronary artery disease. First,
oxidation of LDL cholesterol plays an essential role in macrophage uptake
of LDL and the consequent accumulation of cholesterol plaque. Second,
while intake of antioxidants is believed to decrease oxidation of LDL
cholesterol, perhaps equally important is the role of antioxidants in
improving vasomotion. Endothelial wall function is related to inhibition of
platelet activity and fibrinolysis, critical factors in the pathophysiology of
atherosclerosis.
• An antioxidant-enriched diet maintains healthy arteries that release
vasodilators and fibrinolytic compounds.
• An antioxidant-inadequate diet results in free radical proliferation and
LDL oxidation. Macrophages engulf oxidized LDL, die and form
foam cells in the arterial intima.
• Increased LDL oxidation and foam cell proliferation forms plaque
and blocks the formation of fibrinolytic compounds and vasodilators.
• A clinical event occurs when a 20-30% lumen-obstructing plaque
ruptures.
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• The plaque rupture causes immediate release of clot-forming and
vasoconstriction compounds. Lumen obstructions lead to myocardial
infarction or death.
Epidemiologic studies have shown that an increased consumption of
vegetables and fruits is associated with a decreased rate of coronary artery
disease and increased plasma levels of antioxidants. The antioxidants in
fruits and vegetables appear to decrease the oxidation of LDL cholesterol
and decrease arterial plaque formation. Physicians should encourage
patients to eat at least five to seven servings of vegetables and fruits daily.
Monounsaturated cooking oils and garlic also decrease the oxidation of
LDL cholesterol. In one study, olive oil decreased LDL oxidation and also
decreased macrophage uptake of LDL cholesterol. As previously noted, the
intake of polyunsaturated fat increases oxidation of LDL cholesterol.
Vitamin E obtained from food sources is inversely associated with the risk
of death from coronary heart disease. In one epidemiologic study of 34,486
postmenopausal women, dietary intake of nuts and seeds, concentrated
food sources of vitamin E, was determined to be inversely related to the
risk of death from coronary artery disease. In the Mediterranean diet study,
greater serum levels of vitamin E were detected in patients on the
Mediterranean diet, despite a lower consumption of dietary vitamin E.
From this study, legumes and monounsaturated cooking oils appear to
contain other antioxidants that maintain vitamin E levels.
Dietary Methods of Increasing Antithrombin Activity
The medical literature emphasizes 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.
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.
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Saturated fatty acids and polyunsaturated fatty acids increase platelet
aggregation. 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. 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 alphalinolenic 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, this conversion accelerates greatly, increasing EPA levels 2.5-fold,
when linoleic acid (polyunsaturated fat) intake is limited. Polyunsaturated
fats (corn oil, peanut oil) inhibit the beneficial actions of n-3 fatty acids.
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FIGURE 3. A balanced intake of
polyunsaturated fats (n-6 fatty acids) and
omega-3 (n-3) fatty acids theoretically
produces balanced inflammatory and
thrombolytic activity.
(EPA=eicosapentaenoic acid;
DHA=docosahexaenoic acid)
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. Intake of linolenic acid is strongly associated with a decreased risk of
coronary artery disease.
In one study 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
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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 triglycerides and offer an alternative in the treatment of
hypertriglyceridemia to gemfibrozil, which may be contraindicated 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. 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. 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. 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.
Final Comment
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
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Southern Europeans. Non-dietary lifestyle factors, such as increased
activity, may also influence differences in mortality rates.
Dietary recommendations to their patients should emphasize the addition
of specific beneficial foods, rather than the elimination of foods. Soya
products, legumes, garlic, soluble fiber and nuts rich in monounsaturated
fat all reduce serum LDL cholesterol levels and should be encouraged as
daily staples.
Dietary antioxidants hinder arterial plaque formation and improve
endothelial vasomotor function. In particular, garlic, red wine,
monounsaturated fats, and fruits and vegetables are associated with
decreased oxidation of LDL cholesterol.
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. Patients should decrease their use of saturated fat and trans
fatty acids.
Moderate use of monounsaturated fats decreases LDL cholesterol levels
and LDL oxidation and appears preferable to use of highly polyunsaturated
fats. In contrast to ultra-low-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 antiarrhythmic 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
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acids from fish sources also need to assess the intake of n-3 fatty acids
from plant sources.
A modified antioxidant diet 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.
Patients should eat better by gathering detailed nutritional information; his
is in their own interests.
Food is culture specific and it will be good to follow the traditional
approach. Cross cultural or hybrid diets can do a lot of harm.
The temperature at which a food is cooked will determine the nutritional
value of the item. Generally avoid foods cooked at high temperature.
Avoid deep fried foods.
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