Raised levels of certain lipoproteins are associated with cardiovascular disease. However, it should be emphasised here that while raised levels of these lipoproteins are associated with cardiovascular disease, the cause and effect is not proven. The traditional view was that a raised level of total cholesterol was a risk factor for cardiovascular disease, but this initial theory has been superseded because experimental data and observation did not support this contention. More recently the ratio of low density lipoprotein (LDL) to high density lipoprotein (HDL) has been shown to be a superior predictor of cardiovascular risk. This relates to the observation that while raised levels of the LDL particle are a risk factor for cardiovascular disease, raised levels of HDL are protective of cardiovascular disease. However, the story is more complicated than this because further analysis revealed that there are subdivisions of LDL and HDL particles and these divisions show a heterogeneity of LDL and HDL particle sizes.
Investigations into lipoprotein sizes has shown that high levels of smaller denser LDL particles increase the risk of cardiovascular risk. In contrast higher concentrations of the large buoyant LDL particles does not increase cardiovascular disease risk. Likewise the larger HDL particles are protective of cardiovascular disease, yet the smaller denser particles do not show the same properties. Therefore as the LDL and HDL particles become larger and less dense, the risk of cardiovascular disease diminishes. Raised levels of LDL or HDL are therefore only loosely predictive if the size of the particles has not been quantified. Low carbohydrate diets tend to increase the LDL and HDL particle size. The effect for low carbohydrate diets to increase the peak and mean diameter of the LDL particles is most evident in those with the smallest LDL diameters initially, described as pattern B individuals. Low carbohydrate diets also increase very low density lipoprotein (VLDL) particle size, which may also be cardioprotective1.
Low carbohydrate ketogenic diets have also been investigated for their effects on lipoprotein particle size. For example2, obese subjects fed a low carbohydrate ketogenic diet experienced, compared to the baseline readings, a 78 % reduction in large VLDL, a 60 % reduction in medium VLDL a 57 % reduction in small VLDL, a 54 % increase in large LDL, a 42 % reduction in medium LDL, a 78 % reduction in small LDL, a 21 % increase in large HDL, as well as a 2 % increase in LDL particle size and a 5 % increase in HDL particle size. The low carbohydrate diet group also experienced greater reductions in medium VLDL, small VLDL and medium LDL compared to a low fat energy restricted diet group. In addition the low carbohydrate diet group also experienced greater increases in VLDL, large LDL and HDL particle sizes compared to the low fat energy restricted diet group. Low carbohydrate diets may not lower total cholesterol but they do shift lipoprotein subclasses to a more favourable cardioprotective profile.
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