Exercised: Why Something We Never Evolved to Do Is Healthy and Rewarding

by Daniel E. Lieberman

Cholesterol. A cholesterol test usually measures the levels of three molecules in your blood. The first is low-density lipoprotein (LDL), often termed bad cholesterol. Your liver produces these balloon-like molecules to transport fats and cholesterol throughout your bloodstream, but some LDLs have a harmful tendency to burrow into the walls of arteries, especially when blood pressure is high. These intrusions cause an inflammatory reaction that generates plaques. The second type of cholesterol is high-density lipoprotein (HDL), sometimes called good cholesterol, because these molecules scavenge and return LDLs back to the liver. The third type are triglycerides, fat molecules that are floating freely in the bloodstream and a signpost for metabolic syndrome. To make a long story short, diets rich in sugar and saturated fats contribute to cardiovascular disease because they promote high levels of plaque-forming LDLs. Conversely, physical activity helps prevent cardiovascular disease by lowering triglycerides, raising HDL levels, and to a lesser degree lowering LDL.