HDL basically does the opposite of LDL. While calling HDL-C “good cholesterol” and LDL-C “bad cholesterol” is simplistic, studies do show that a lower ratio of HDL-C to LDL-C (and of HDL-C to total cholesterol) leads to a higher risk of cardiovascular disease (CVD). Those ratios matter more than your absolute numbers for HDL-C, LDL-C, and even total cholesterol.
A WHO meta-analysis reported that eating more saturated fat increased HDL-C, but the increase was one-tenth that of LDL-C. Therefore, the ratio of LDL-C to HDL-C (and of total cholesterol to HDL-C) increased, and with it the risk of heart disease.
A similar pattern was seen with apoA1, the major protein component of HDL particles, akin to apoB for LDL particles. Although replacing unsaturated fat by saturated fat led to increases in apoA1, the increase was only 30–60% that in apoB. The ratio of apoB to apoA1 is considered a better predictor of heart-disease risk than other blood lipid biomarkers and their ratios. If apoB increases more than apoA1, then the apoB-to-apoA1 ratio increases, and with it the risk of heart disease.
The HDL-C and apoA1 numbers reflect the amount of HDL in the blood. HDL has cardioprotective effects, but while eating saturated fat (instead of unsaturated fat) increases both HDL-C and apoA1, it increases LDL-C and apoB even more.
The ratio of triglycerides to HDL-C represents a strong, independent predictor of heart disease when LDL-C levels are below 160 mg/dL, and has similar predictive ability as LDL-C for determining the extent of atherosclerosis in at-risk patients. Having a ratio of triglycerides to HDL-C above 3.8 is associated with having more small, dense LDL particles, which are especially susceptible to oxidation.
The aforementioned WHO meta-analysis reported that eating more polyunsaturated fat reduced the ratio of triglycerides to HDL-C, whereas eating more carbohydrate increased it, when saturated-fat intake was reduced. However, the changes were very small and not clinically significant. A 10% reduction in calories from saturated fat would increase the ratio of triglycerides to HDL-C by a mere 0.16 if more carbohydrate were eaten, and decrease it by only 0.04 if more polyunsaturated fat were eaten.
The ratio of triglycerides to HDL-C correlates with the number of small, dense LDL particles and represents a strong risk factor for heart disease. However, changes in saturated-fat intake have little effect on this ratio.