When the twins decreased their fat intake their high-density lipoprotein (HDL)-cholesterol, the so-called "good cholesterol," fell in both the active and the sedentary twin. There was also a significant drop in apo A-I levels, the major protein of the HDL particles, in the active twin, and a nearly significant decrease in the sedentary twin. Combining the dietary response of the active and inactive twin confirmed the significant reduction in apo A-I, and the increase in an atherogenic lipoprotein particle called lipoprotein(a). Plasma levels of low-density lipoprotein (LDL) cholesterol, the "bad cholesterol", did not change in response to the diet. The LDL-cholesterol is carried on particles of different sizes, and the smaller particles are particularly dangerous in regards to heart disease. Switching from the high-fat, low carbohydrate diet to the low-fat, high-carbohydrate diet caused a significant decrease in the overall average size of the LDL-particles. This was due to an increase in the concentrations of the smaller atherogenic LDL-particles, and a decrease in the concentrations of larger particles, whose relationship to heart disease is less certain. There was a wide range of responses to the diet, with some twins decreasing their LDL-cholesterol levels when switching to a lower-fat, higher-carbohydrate diet, and others not. The figure below is a scatterplot of the twins' changes in LDL-cholesterol. Each point represents one twin pair. A line drawn from the point down to the horizontal axis shows the LDL-cholesterol change