Vegetarianism and cardiovascular diseases

Heart disease and stroke currently account for 42% of deaths in Australia. A raised level of cholesterol in the blood is a risk factor for heart disease, and high blood pressure is a risk factor for stroke. The cost of treating these diet-related diseases in 1992 was estimated as follows (1):

An average drop of 5% in cholesterol levels has been estimated to produce a saving of $5.4 million in medical expenditure at 1987 costs in NSW alone (2).

Cholesterol and heart disease

Only in countries where average cholesterol levels are over 5.2mmol/l is coronary heart disease common (3).

Cholesterol is found only in animal foods (meats, seafood, eggs, dairy products) - there is no cholesterol in plant foods. When people's cholesterol levels are too high, it is usually because they eat too many animal products containing cholesterol and saturated fat. A small minority of people have high levels because their body produces too much cholesterol.

A number of studies have shown that vegans or near-vegans have much lower total cholesterol and Low Density Lipoprotein (LDL) levels than meat eaters (4-7). It is the LD Lipoprotein that transports cholesterol to the artery walls, where it forms plaques that narrow the arteries. Therefore, it is desirable to have low LDL levels as well as low total cholesterol.

Vegans have lower total and lower LDL cholesterol levels than lacto-ovovegetarians (8). However, even lacto-ovovegetarians have lower cholesterol levels than meat eaters. This difference is due to diet because it exists even when largely vegetarian Seventh Day Adventists are compared to similarly clean living, but meat eating Mormons (9).

The difference is already found among teenagers - 12-17 year old vegetarian SDAs had a 19% lower cholesterol level than otherwise similar meat eating teenagers. Of the meat eating group, 12% had a cholesterol level over 6.2mmol/l, and so were already laying the foundations for heart disease later in life (10).

With the typical Western, meat-based diet, children and young adults already have signs of atherosclerosis (11). In a large US study of cardiovascular risk factors, young people who died (largely as a result of trauma) were autopsied. Half the 2-15 year olds had fatty streaks in the coronary arteries, and 8% had fibrous plaques. This incidence increased with age: 85% of 21-39 year olds had fatty streaks in the coronary arteries, and 69% had fibrous plaques. The extent of atherosclerosis was linked to the risk factors of high body mass index (obesity), high blood pressure, high LDL cholesterol, and high triglycerides, all factors which are less common in vegetarians.

In a comparison of 6000 vegetarians with meat eating friends and relatives, vegans had lower total and lower LDL cholesterol levels than vegetarians, and both had lower levels than meat eaters. On the basis of these differences, the researchers estimated that lifelong vegetarians had a 24% lower risk of heart disease, and lifelong vegans a 57% lower risk (12).

Vegetarians were less likely to die of heart disease, even when they were compared to a relatively healthy group of meat eaters selected from health shop customers (13).

Among the Californian Seventh Day Adventists, there was a clear relationship between the amount of meat eaten and the risk of dying of heart disease. Men aged 45-64 who ate meat daily were 3 times more likely to die of heart disease than those who didn't eat meat (14). The difference was smaller but still significant for older men, and for women over 65.

A large Chinese study clearly demonstrated the value of a plant-based diet in preventing high cholesterol and heart disease (15). Deaths in 130 villages in 65 counties were related to dietary factors. The death rate due to coronary artery disease in the group 0-64 years was 4/100,000 for men and 3.4/100,000 for women in China, compared to 66.8/100,000 for men and 18.9/100,000 for women in the US. The Chinese ate only 10% as much animal protein as in the typical US diet, with half as much fat and three times more fibre. The average blood cholesterol level of the Chinese (127mg/dl) was only 63% that of the average American (203mg/dl), and well below the level where heart disease becomes a problem.

The researchers concluded:
" First, a diet comprising a variety of good-quality, plant-based foods yields the lowest disease rates. Second, there is no evidence of a threshold beyond which further benefits do not accrue with increasing proportions of plant-based foods in the diet. Our study results have convinced us that consumption of a low-fat, plant-based diet can prevent and reverse a wide variety of chronic degenerative diseases. "

Iron and heart disease

Some studies show a link between heart attacks and high intake of haem iron, which comes only from animal products, especially red meat. A large US study of male health professionals aged 40-75 found that those with the highest intake of haem iron were 1.42 times more likely to have a heart attack than men with the lowest intake, even when other risk factors were taken into account (16). The risk was particularly great for fatal heart attacks: those with the highest intake were 2.33 times more likely to have a fatal heart attack and 1.44 times more likely to have a non-fatal heart attack than men with the lowest haem iron intake.

In the Rotterdam study of people aged over 55, those with the highest intake of haem iron were 1.83 times more likely than those with the lowest intake to have a heart attack (17). Considering only the first heart attack, those with the highest intake were 3.77 times more likely to have a fatal attack and 1.59 times more likely to have a non-fatal attack than those with the lowest haem iron intake.

So, apart from its contribution to atherosclerosis in terms of saturated fat and cholesterol, meat can also contribute to the risk of heart attack through its haem iron content when a person already has other risk factors for heart disease.

Diet as therapy

Vegetarian diets

Several studies have shown that vegetarian diets can reduce total and LDL cholesterol levels (18-24). In one study, reductions of 12.5% in total cholesterol and 14.7% in LDL cholesterol occurred in normal people after only 3 weeks on a low-fat diet, which was vegan except for skim milk (19). In another study, normal women following a low-fat vegan diet for 2 months reduced total cholesterol by 13.2% and LDL cholesterol by 16.9% (20).

Intensive lifestyle changes, including low-fat vegetarian diet, exercise and stress management, produced dramatic changes over 12 months in men with existing atherosclerosis (21). Total cholesterol was reduced by 24% and LDL cholesterol by 37%. In most people (82%) the extent of atherosclerotic plaques decreased, whereas in over half the control group atherosclerosis progressed. Frequency, severity and duration of angina attacks decreased dramatically, whereas in the control group angina increased. Virtual elimination of angina due to a vegan diet has also been demonstrated in an earlier study (22).

People who followed the intensive lifestyle changes for 5 years continued to show benefits, even though they did not adhere to the program as well as previously. They still had an average reduction in initial LDL cholesterol of 20% even though no-one was taking medication, reduced frequency of angina, and reduction of atherosclerotic plaques (23). In contrast, over half the control group was taking medication to reduce cholesterol and angina, and atherosclerotic plaques continued to worsen. The vegetarian group had only 40% of the coronary events (surgery, heart attack, etc) suffered by the control group over 5 years.

In another study, 18 people followed a low-fat vegetarian diet for 5 years, and reduced their average cholesterol levels from a high 237mg/dl to 137mg/dl (24). All but one continued the diet for another 7 years, at which time average cholesterol was still 145 mg/dl. During the 12 years of the study, there were no coronary events, even though the 18 people had experienced 49 coronary events between them in the 8 years before the study.

Clearly a vegetarian, and especially a vegan diet is effective in reducing cholesterol and even in reversing existing heart disease. The Heart Disease Prevention Manual, written by a nutritionist and a pharmacist, concludes (25):
" So impressive are the health benefits of vegetarian diets, that some researchers feel that a vegetarian diet may be the best diet for treating coronary artery disease, angina and high blood fats ".

Soy protein

There is now a lot of interest in the cholesterol-lowering potential of soy protein. A review of 20 studies involving patients with high cholesterol showed that in 60% of the studies average cholesterol was dramatically improved when soy protein was substituted for animal protein in the diet, improvements ranging from 10% to a high 34% (26). In the remaining 8 studies, improvements were smaller or did not eventuate. Little reduction was achieved in studies where subjects had normal cholesterol to start with.

In another review of research, in 34 of 38 studies, substituting soy protein for animal protein reduced total cholesterol and LDL cholesterol. In the remaining 4 studies participants already had low levels of cholesterol (27).

Similarly another research group, on the basis both of its own work over 20 years with over 1000 patients, and an extensive literature review, concluded that soy in the form of Textured Vegetable Protein reduces cholesterol in people who are clearly hypercholesterolemic (28).

In more recent studies, both men and women and people with various cholesterol levels have been shown to benefit from soy. In one study meals were provided for men, the protein coming either from soy or animal products. The soy diet reduced the average LDL cholesterol levels of both normal and hypercholesterolemic men by 6%, and the LDL:HDL cholesterol ratio by 11% (29). In a study of postmenopausal women with high cholesterol, either milk protein or soy protein was added to the Step 1 diet recommended by the US National Cholesterol Education Program. The soy protein reduced LDL cholesterol and the LDL:HDL ratio significantly more than the milk protein diet (30).

There is considerable evidence that soy protein reduces cholesterol in people who have high levels, although its effect is less clear in normal people.

Lean meats and fish

Much attention has focussed on fish as a way of reducing heart attacks. Some studies show a beneficial effect of fish, while others do not. In one large study, involving over 40,000 men over 6 years, those who ate the most fish were slightly more likely to have heart surgery and to die of a heart attack than those men who ate little fish. However, men who ate no fish were more likely to die of heart disease than men who ate some fish (31).

In another study, men who ate more than 30gr of fish a day were more than twice as likely to suffer a heart attack and to die of heart disease than men who ate less than this amount (32). The authors hypothesised that the result may be due to the high mercury contamination of some fish, as a result of environmental pollution.

Some studies have investigated whether different kinds of meats can be used to improve cardiovascular health, with limited success. In one study participants ate only beef, then only poultry, then only fish, each for a 3 month period (33). In a further study participants ate only red meat, and then only fish and poultry, each for a 6 week period (34). In neither study did the type of meat have an effect on cholesterol levels. So, eating fish and chicken is not an effective way to reduce cholesterol.

In a recent study, men and women with raised cholesterol levels followed the US National Cholesterol Education Program Step 1 diet, where no more than 30% of calories come from fat, and daily intake of cholesterol is no more than 300mg (35). Participants were counselled to eat 170 grams of lean meat a day, 80% of which was to be either red meat or white meat. After 9 months, the group eating red meat decreased total cholesterol by 1.0% and LDL cholesterol by 1.7%, while the group eating white meat decreased total cholesterol by 1.8% and LDL cholesterol by 2.9%. Clearly eating red or white meat doesn't make much difference, and cholesterol reductions will never be large while people are eating meat at all.

Some studies have directly compared the effects of vegetarian diets with those recommended by health authorities. For example, men and women with raised cholesterol followed a low-fat diet with 62% of protein from animal sources for 3 weeks, or a diet in which 93% of protein was from plants, mainly soy (36). The soy group reduced blood cholesterol by an average of 21% after 3 weeks, whereas the low-fat diet containing animal products was essentially ineffective.

In another case, a lacto-ovovegetarian diet was compared with a "prudent" diet containing lean mean and no more than 30% of calories from fat, as recommended by the National Heart Foundation. After 6 weeks, the vegetarian diet reduced total cholesterol by 10%, compared to only 5% with the lean meat diet. Decreases in LDL cholesterol were also significantly greater following the vegetarian diet (37).

Clearly low-fat vegetarian and especially vegan diets are most effective in preventing coronary artery disease, and in reversing it once it is established. Soy products may have a special role to play in this beneficial effect. In spite of these findings, health authorities continue to recommend lean meats, especially chicken, and allow up to 30% of calories in the diet to come from fat. Studies that have achieved spectacular results (eg 21, 24) prescribe vegetarian diets and allow no more than 10% of calories from fat. As one of these researchers commented (24):
" Despite the benefits of a low-fat diet and of low lipid levels, the American Heart Association, the National Research Council, and the National Cholesterol Education Program recommend a 30% threshold for fat calories in the diet and a total cholesterol not greater than 200mg/dl. But coronary artery disease develops and progresses with these guidelines, condemning millions of Americans to this epidemic. "

The evidence is clear: people who are serious about lowering their cholesterol levels, improving their cardiovascular health, and reducing their risk of heart attack, should turn to a low fat vegetarian, and especially vegan diet, getting their protein from plant sources, especially soy.

High blood pressure and stroke

Many people in western societies are hypertensive (have high blood pressure), which increases their risk of heart failure and stroke. As one researcher has commented:
" At present, 15-20% of adults in westernized societies are so labelled, most of them with mild blood pressure elevation and receiving anti-hypertensive drug therapy. Recent drug trials have demonstrated how very large numbers have to be treated for relatively small returns in terms of prevention of stroke and heart failure, and with substantial burdens in terms of drug side effects, inconvenience and financial costs " (38).

Vegetarians have lower blood pressure and are less likely to be classed as hypertensive. Vegetarian diets have been used as therapy to reduce blood pressure, without the costs and side effects of drugs.

Lower blood pressure due to diet has been demonstrated by comparing meat eating and vegetarian Seventh-Day Adventists (39), Mormons with Seventh-Day Adventists (9), Israeli vegetarians with meat eating hospital staff (40), macrobiotics with the general population (41), and Seventh Day Adventists with meat eating volunteers (42).

Among meat eating Seventh Day Adventists (SDAs), 44% of blacks and 22% of whites were taking prescribed medication for high blood pressure, compared to only 18% of blacks and 7% of whites among the vegetarians (39). In the Israeli study, 26% of meat eaters but only 2% of vegetarians were classed as hypertensive (40). Similarly, 10% of a Mormon group, but only 1-2% of an SDA group were classed as having mild hypertension (9). This comparison shows that it is diet rather than other factors (tobacco, alcohol, caffeine) which makes the difference. Both Mormons and SDAs are encouraged to abstain from harmful substances, but SDAs are also encouraged to abstain from meat.

High blood pressure is a risk factor for stroke. Not surprisingly, vegetarians are less likely to die of stroke. In over 25,000 Californian SDAs who were studied for 21 years, the risk of dying of stroke was reduced by over 20% compared to the general population (43).

Vegetarian diets have been used as therapy for high blood pressure. Several studies have shown that a lacto-ovovegetarian diet for 6 weeks produces a decrease in blood pressure in both normal (44) and mildly hypertensive people (45-46). A 5% reduction in blood pressure, as achieved in these studies, was estimated to produce a 7% reduction in major coronary events (46).

Much more dramatic effects have been achieved with vegan diets. In a Swedish study, patients on medication adopted a vegan diet and other healthy lifestyle changes for 1 year. Their average blood pressure was lower, even though 77% of the patients came off medication and the remainder took only about half as much. Prior to the study, patients reported an average of 3.7 symptoms associated with high blood pressure. After 1 year, 85% of patients had no symptoms at all, and the remainder had only 1 or 2 that were less pronounced (47).

In another example, patients were either in a 9 week out-patient program or a 25 day live-in program (48). In both cases patients lost weight, decreased their blood pressure and, in many cases, came off medication. For example, in the live-in program after only 3 weeks, 66% of the women who were on medication at the start of the program and 72% of the men, were able to give up their drugs and still maintain normal blood pressure. In spite of the reduced medication, systolic blood pressure decreased by 18 points for women and 19 points for men over a 3-week period, very much more than in the vegetarian studies (44-46), where much more minor dietary changes were made.

A vegetarian, but especially a vegan diet, can substantially reduce blood pressure and the risk of stroke and heart disease, without the financial costs and adverse side effects associated with drugs.

I would like to see References for this document on Vegetarianism and Cardiovascular Diseases.

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