Blood levels of cholesterol, the fatty substance that can build up in your arteries, can go as high as 700. Yes, 700! But those who attain the 700 number have a rare genetic disorder—familial hypercholesterolemia—in which cholesterol levels are high, regardless of diet or exercise, according to Lynne Perry-Böttinger, MD, FACC, a board-certified clinical and interventional cardiologist in New Rochelle. According to the National Institutes of Health, only about one in 500 people in the country are so afflicted.