roponents of the cholesterol theory of cardiovascular disease believe that dietary cholesterol and saturated fatty acids are the cause of cardiovascular disease. The mechanism for this we are told is based on the erroneous belief that dietary cholesterol and saturated fat are able to detrimentally affect levels of certain plasma lipoproteins, which are in turn a risk factor for cardiovascular disease. That the nutritional literature does not support this contention is seemingly ignored. In fact the evidence for such a belief is so slim, that it would be just as scientific to suggest that the magic cholesterol fairy is the cause of cardiovascular disease. A number of studies are often cited by proponent of the cholesterol theory of cardiovascular disease, as evidence to support their viewpoint. However, when these studies are analysed it becomes clear that the results are easily explainable by the presence of confounding variables.
One such problem with using low fat diet studies to show that lowering dietary cholesterol and saturated fat decreases plasma levels of cholesterol is the fact that low fat diets tend to change their composition. Lowering the fat usually entails increasing carbohydrate content of the diet, and this in turn increases the fibre intake. As fibre is known to lower plasma cholesterol levels, it is not possible to conclude that low fat diets lower plasma cholesterol from such studies. In addition, lowering the fat content of the diet has been reported to cause significant alterations to the composition of the diet as a whole. For example, in one study1 published in the American Journal of Clinical Nutrition, researchers reported on the dietary composition seen with changing from a 40 to 44 % fat diet to a more modest 25 % fat diet. Such a dietary practice might be employed by an individual persuaded to lower their fat intake based on current medical recommendations.
The results of this study showed that reducing the fat content of the diet as a whole also reduced the cholesterol, saturated fat and monounsaturated fat content of the diet. This was accompanied by an increase in polyunsaturated fat. This is problematic for the proponents of the cholesterol theory of cardiovascular disease, because polyunsaturated fatty acids of the omega 3 variety are known to lower the risk of cardiovascular disease and cause reductions in fasting triglyceride levels. In addition, the lower fat diet increased dietary intakes of a number of micronutrients including vitamin C, thiamine, riboflavin, niacin, B6, B12 and folate. The B vitamins B6, B12 and folate are known to lower cardiovascular risk because they decrease plasma homocysteine concentrations, high levels of which are able to cause endothelial dysfunction and vascular damage. Vitamin C may also protect from cardiovascular disease because it lowers levels of lipoprotein(a).
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