There are different types of LDL particles, and some of them are more likely to contribute to heart disease than others. LDL particles range from large and fluffy to small and dense, and it is the smaller, denser particles that cause the problems. The large fluffy LDL particles play little role in developing heart disease. So not only should we be counting the number of LDL particles, we should also note their sizes.
It is well known (by which I mean it is part of the Conventional Wisdom) that vegetable oils are good for the heart. Vegetable oils (that’s corn, safflower, canola, soybean, sesame etc) have been shown to reduce LDL (that is not just part of the Conventional Wisdom, that is actually true), so surely they lower the risk of heart disease, right?
Vegetable oils tend to be higher in polyunsaturated fats, and polyunsaturated fats are more easily oxidised than saturated fats. Oxidised LDL is far more likely to become stuck in the arterial wall. Vegetable oils reduce the number of large fluffy LDL particles, but leave the SDLDL particles behind. Although vegetable oils will reduce the total number of LDL particles, they will increase the number of SDLDL, and actually increase your risk of heart disease. (The cooking temperature also matters – see this post for more on cooking oils.)