An analysis of five recent studies, including more than 76000 cases, showed that mortality from coronary heart disease was 31% lower among vegetarian men compared to non-vegetarians, and 20% lower among women. In the only study on this subject, conducted among vegans, the risk of developing the disease was even lower among vegan men than among ovo-lacto-vegetarian men.
The ratio of deaths was also lower among vegetarians, both men and women, compared to semi-vegetarians; those who ate only fish, or those who ate meat no more than once a week.
The reduced rate of cardiovascular disease among vegetarians is due to their lower levels of cholesterol in their blood. A review of 9 studies found that lacto-ovo vegetarians and vegans had 14% and 35% lower blood cholesterol levels than non-vegetarians of the same age, respectively. It may also explain the lower body mass index among vegetarians.
Professor Sacks and colleagues found that when a vegetarian subject was heavier than a non-vegetarian, there were markedly fewer lipoproteins in his plasma. Some, but not all, studies show reduced blood levels of high molecular density lipoprotein (HDL) among vegetarians. Decreased HDL levels can be caused by a general decrease in dietary fat and alcohol intake. This may help explain the small difference in rates of cardiovascular disease among vegetarian and non-vegetarian women, as High-density lipoprotein (HDL) levels in the blood may be a greater risk factor for disease than low-molecular-density lipoprotein (LDL) levels.
The level of common triglycerides is approximately equal among vegetarians and non-vegetarians.
A number of factors specific to a vegetarian diet can affect blood cholesterol levels. Although studies show that most vegetarians do not follow low-fat diets, saturated fat intake among vegetarians is significantly lower than among non-vegetarians, and the ratio of unsaturated to saturated fats is also significantly higher in vegans.
Vegetarians also get less cholesterol than non-vegetarians, although this figure varies among groups where studies have been conducted.
Vegetarians consume 50% or more fiber than non-vegetarians, and vegans have more fiber than ovo-lacto vegetarians. Soluble biofibers may reduce the risk of cardiovascular disease by lowering blood cholesterol levels.
Some studies suggest that animal protein is directly linked to high blood cholesterol levels.even when all other nutritional factors are carefully controlled. Lacto-ovo vegetarians consume less animal protein than non-vegetarians, and vegans consume no animal protein at all.
Studies show that eating at least 25 grams of soy protein per day, either as a substitute for animal protein or as a supplement to a normal diet, lowers blood cholesterol levels in people with hypercholesterolemia, high blood cholesterol. Soy protein can also increase HDL levels. Vegetarians eat more soy protein than regular people.
Other factors in a vegan diet that reduce the risk of cardiovascular disease, other than the effect on blood cholesterol levels. Vegetarians consume significantly more vitamins – antioxidants C and E, which can reduce the oxidation of LDL cholesterol. Isoflavonoids, which are phyto-estrogens found in soy foods, may also have anti-oxidant properties as well as enhance endothelial function and overall arterial flexibility.
Although information on the intake of certain phytochemicals among various populations is limited, vegetarians show higher intakes of phytochemicals than non-vegetarians, as a greater percentage of their energy intake comes from plant foods. Some of these phytochemicals interfere with plaque formation through reduced signal transduction, new cell formation, and triggering anti-inflammatory effects.
Researchers in Taiwan found that vegetarians had significantly higher vasodilation responses, directly related to the number of years a person spent on a vegetarian diet, suggesting a direct positive effect of vegetarian diet on vascular endothelial function.
But reducing the risk of cardiovascular disease is not only due to the nutritional aspects of vegetarianism.
Some but not all studies have shown elevated blood levels of homocysteine in vegetarians compared to non-vegetarians. Homocysteine is thought to be an independent risk factor for cardiovascular disease. The explanation may be insufficient intake of vitamin B12.
Vitamin B12 injections lowered blood homocysteine levels in vegetarians, many of whom had reduced vitamin B12 intake and elevated blood homocysteine levels. In addition, a reduced intake of n-3 unsaturated fatty acids and an increased intake of saturated n-6 fatty acids to n-3 fatty acids in the diet may increase the risk of heart disease among some vegetarians.
The solution may be to increase the intake of n-3 unsaturated fatty acids, for example, increase the intake of flaxseed and flaxseed oil, as well as reduce the intake of saturated N-6 fatty acids from foods like sunflower oil.