Do you have high cholesterol, also known as hypercholesterolemia? Abnormal cholesterol levels such as high LDL cholesterol or low HDL cholesterol are a major risk factor for heart disease and stroke. An unhealthy diet can cause high cholesterol. Sometimes high cholesterol runs in families. A low-cholesterol diet can help improve cholesterol levels. If the low-cholesterol diet does not work to lower bad cholesterol and increase good cholesterol, your doctor may prescribe medications.