Coronary heart disease has become one of the biggest killers in modern societies, and the consumption of animal fats has been positively associated with this phenomenon. Arteriosclerosis does not only lead to heart disease, but can also be responsible for strokes and kidney diseases. Arteriosclerosis is a slow insidious disease which progresses slowly as a result of the deposition of fat and cholesterol in the walls of the arteries. These fatty deposits become hardened, making the blood vessels less elastic, and eventually clogging them with plaque (a mass of fat and cholesterol). It sometimes happens that blood platelets become caught on the rough edges of plaque, thus initiating clot formation. In this way blood flow to the tissues can be further diminished or stopped. If a clot stays in place it is called a thrombus but if it becomes dislodged and travels around it is called an embolus. Clogged blood vessels in turn
lead to a host of secondary effects such as ischaemia (lack of blood supply and oxygen in the area supplied by the blood vessel) or coronary or cerebral infarct where the supply of oxygen is completely cut off as in the case of a heart attack or stroke. Angina attacks are an indication that the coronary arteries are clogged to the extent that only a quarter of the normal blood supply is being sent to the heart muscle.
It has been clearly established that high cholesterol levels can pose a serious risk of contracting cardiovascular diseases. Besides cholesterol, there are other compounding factors which increase the risk of getting a heart attack, such as high blood pressure and smoking. What is more, the risk is more than additive, as being exposed to more than one of these factors will more than double the risk of having a heart attack. Cholesterol levels per se are however not necessarily a good indicator of the overall risk, but it seems as if the relationship between HDL- and LDL-cholesterol is a better criterion to use when determining the risk factor. HDL-cholesterol has been firmly established as a predictor of protection from atherosclerotic disease. People with low HDL cholesterol levels have the highest heart attack rates, even if their cholesterol levels are in the supposedly safe range of 116 to 192 mg/dl for men and 124 to 211 mg/dl for women. LDL-cholesterol, on the other hand, appears to remain a risk factor throughout life.17
An elevated serum triglyceride level is also a risk factor for arteriosclerosis. This could be because high triglyceride levels are associated with low HDL-cholesterol levels. When triglyceride metabolism is efficient, the triglyceride concentration is low and the HDL concentration is high. When triglyceride metabolism is sluggish, the triglyceride concentration is high and the HDL concentration is low.18 Elevated triglyceride levels will also lead to obesity which has also been established as a leading cause of disease. The incidence of obesity also increases with age, as do the risks of contracting cardiovascular disease.
The ratio of saturated to unsaturated fats in the diet is also of significance when determining the risk of contracting cardiovascular disease. Saturated fat is highly correlated with the incidence of coronary heart disease.6 A high intake of total fat, cholesterol and saturated fatty acids can also lead to thrombosis, as such diets increase the levels of fibrinogen and factor VII which could cause an increase in thrombosis tendency. Clinical studies have shown, that stearic acid is the most thrombogenic fatty acid,6 and diets high in animal products will thus increase the risk of thrombosis. Research has focused for many years on the benefits of polyunsaturated fatty acids in the diet, and these fats have become the desirable replacement for saturated fats to lower cholesterol levels. However, this practice has raised some concern, as studies showed that polyunsaturated fats lowered the levels of the desirable HDL-cholesterol, which was not the case if foods rich in monounsaturated fatty acids were consumed.19,20 Moreover, it was found that diets high in polyunsaturated fats increased the cancer risk21 and had a negative influence on the immune system.22 Trans fatty acids in the diet have been positively associated with cardiovascular disease. In the Nurses’ Health Study, 23 a 50% increase in risk of heart disease in the highest versus the lowest levels of trans fatty acid consumption was reported, although there were no differences at the intermediate level of consumption. Clinical studies have also shown, that hydrogenated vegetable fats (corn, soy, cottonseed, peanut, or safflower) consistently increased blood cholesterol levels compared to the natural unhydrogenated oils.6 Mediterranean diets rich in monounsaturated fats, on the other hand, seem to afford protection against heart disease and cancer.
Mediterranean diets include mainly olive oil as the main fat, and they contain lower levels of polyunsaturated and saturated fats. Mediterranean diets are also rich in grain products such as all kinds of breads, baked goods and pastas. They also include many legumes, seeds, nuts, fruits and vegetables. Populations on this type of diet have low cholesterol levels and a low incidence of coronary heart disease compared to counterparts in other regions of the same country.21 Olives, canola oil, monounsaturated safflower and sunflower oils, and almonds are rich in oleic acid which is a monounsaturated fatty acid. In figure 3.7 the relationship between the various fatty acids in foods commonly used in Mediterranean countries is presented.
Vegan vegetarians consume very similar foods to those prevalent in Mediterranean diets. It has also been established that a vegan vegetarian diet can afford protection against cardiovascular diseases. Vegan vegetarians have lower LDL-cholesterol and triglyceride levels than are prevalent in the general population, but HDL-cholesterol levels are not depressed.25 Thus the ideal relationship between these components can be maintained by a vegan diet and this lifestyle can help both adults and children to maintain or achieve desirable blood lipid levels. In view of the increase in the prevalence of cardiovascular diseases with age, a vegan vegetarian diet can contribute substantially to the quality of life during old age. There is also quite a body of evidence, that coronary lesions can even be reversed by extremely stringent diets combined with other lifestyle changes.26 Having said this, it is essential to note, that stringent lifestyle changes may be acceptable for adults who want to reduce fat intake to prevent cardiovascular disease, but care should be taken not to enforce similar changes on children, who require higher fat intakes than adults.27 For a more detailed discussion of these criteria see chapter 5.