Cholesterol is transported in the bloodstream in the form of what are known as 'lipoproteins'. Basically, these are tiny packages of cholesterol and fat, encased in a mix of fats (known as phospholipids) and protein. Lipoproteins come in two different forms: 'low-density' and 'high density'. High-density lipoprotein (HDL) has links with a reduced risk of heart disease, while low-density lipoprotein (LDL) is linked with heightened heart disease risk. This is basically why HDL and LDL are often referred to as 'good' and 'bad' cholesterol respectively.

While LDL-cholesterol has been painted as a villain where heart disease is concerned, increasing evidence shows that not all LDL-cholesterol is bad. LDL-cholesterol varies in size, ranging from small, dense particles up to much larger, less-dense ('fluffy') particles. It has been known for a long time that the size and density of LDL particles has an important bearing on apparent risk of heart disease. What the evidence shows is this: small, dense LDL particles are associated with an increased risk of heart disease, while large, 'fluffy' LDL particles are not [1].

A useful analogy to think of the potential damage wreaked by different types of LDL is to think of large, 'fluffy' LDL as a tennis ball, and small, dense LDL as a golf ball. If we were to throw each of these at a window, it's fair to say that the golf ball is quite likely to break the window, while the tennis ball is likely just to bounce off.

While we're encouraged to eat a low-fat diet for the sake of our cardiovascular health, there is some evidence that this strategy can have a detrimental effect on LDL particle size. In one study, individuals were fed a low-fat, high-carbohydrate diet for four weeks. On a separate occasion, the volunteers were then fed a high-fat, low-carbohydrate diet for the same length of time [2]. Compared to the low-carbohydrate diet, the low-fat one led to a reduction in the size of the LDL particles (not a good thing). In another study, adopting a low-carbohydrate diet was found to increase LDL particle size [3].

This evidence suggests that the low-fat, high-carbohydrate diet so commonly advocated for heart disease prevention can lead to changes in LDL size (making LDL smaller and denser) - a change that is actually associated with enhanced risk of heart disease. It's another reason to be mistrustful of conventional dietary advice regarding the prevention of heart disease.

Here's to a healthy heart.


1. Austin MA, Low-density lipoprotein subclass patterns and risk of myocardial infarction. JAMA. 1988;260(13):1917-21

2. Faghihnia N, et al. Changes in lipoprotein(a), oxidized phospholipids, and LDL subclasses with a low-fat high-carbohydrate diet. J Lipid Res. 2010;51(11):3324-30 3. Volek JS, et al. Modification of lipoproteins by very low-carbohydrate diets. J Nutr. 2005;135(6):1339-42