The cholesterol theory of cardiovascular disease states that dietary cholesterol and saturated fatty acids are the cause of atherosclerosis, which is in turn is the cause of cardiovascular disease. However, this theory is so shot full of holes it is difficult to know where to begin when discussing it. The main problem with the theory is that dietary cholesterol and saturated fatty acids do not cause deleterious changes to plasma lipoprotein levels in healthy individuals. In fact, the liver manufactures larger quantities of cholesterol than are present in the diet of most individuals and saturated fat is not a single substance, but a group of chemicals, the constituents of which all have different physiological effects. Another problem is that changes to lipoprotein levels when they do occur, have not been shown to cause cardiovascular disease, only be associated with it. In fact, it is likely the development of the metabolic syndrome is the common factor that links changes to plasma lipoproteins to the development of cardiovascular disease.
Another of the problems surrounding the cholesterol theory of cardiovascular disease is the more recent research findings surrounding endothelial dysfunction. It has become apparent that other dietary factors may be the root cause of cardiovascular disease because they cause changes to the endothelial lining which in turn changes the flow characteristics and blood pressure. In particular it is thought that free radicals and oxidative stress interfere with the production of nitric oxide through inhibition of the enzyme nitric oxide synthase. Because nitric oxide is required for correct relaxation of the arteries, its inhibition prevents the normal relaxation that occurs in response to flow (flow mediated dilation). Antioxidant nutrients have been shown to increase production of nitric oxide and reverse deleterious changes to flow mediated dilation, suggesting that the dietary origins of cardiovascular disease can be traced to food that cause oxidative stress rather than the presence of lipids.
A recent study published in the American Journal of Clinical Nutrition investigated the ability of saturated fatty acids to cause endothelial dysfunction1 in human subjects. The study involved feeding over one hundred subject with insulin resistance a high saturated fat diet for one month, followed by either a high saturated fat, high carbohydrate or high monounsaturated fat diet for 24 weeks. The researchers then monitored the changes in flow mediated dilation caused by the different diets. The results showed that there were no significant differences between the different diets in terms of the degree of flow mediated dilation. Therefore it cannot be said that dietary saturated fatty acids detrimentally affect endothelial function, flow dynamics or blood pressure in arteries. As endothelial dysfunction is likely required to cause the arterial stiffness associated with atherosclerosis, this suggests that saturated fat is not involved in this process, or at least not on the short time scale seen in this study.
Dr Robert Barrington’s Nutritional Recommendation: Cardiovascular disease is likely not caused by dietary cholesterol or saturated fat. Instead it may be caused by the consumption of a low quality diet that leads to the development of a raft of metabolic abnormalities that can be termed the metabolic syndrome. These changes include a dysfunction in the endothelial lining of the arteries that affect correct blood flow which in turn leads to damage to the endothelial lining of the arteries. Such diets also cause the deleterious changes to blood lipids that are associated with (but not the cause of) cardiovascular disease. Eating a high quality diet and abandoning the typical Western diet is effective at reversing the metabolic syndrome, which in turn will reduce the risk of cardiovascular disease significantly.
RdB
