What is diabetes? The term diabetes refers to a group of diseases that affect the way your body uses blood glucose, commonly called blood sugar. Glucose is vital to your health because it’s the main source of energy for the cells that make up your muscles and tissues. It’s your body’s main source of fuel. If you have diabetes — no matter what type — it means you have too much glucose in your blood, although the reasons why may differ. And too much glucose can lead to serious problems. To understand diabetes, it helps to understand how your body normally processes blood glucose. Processing of blood glucose Blood glucose comes from two major sources: the food you eat and your liver. During digestion, glucose is absorbed into your bloodstream. Normally, it then enters your body’s cells, aided by the action of insulin. The hormone insulin comes from your pancreas. When you eat, your pancreas secretes insulin into your bloodstream. As insulin circulates, it acts like a key, unlocking microscopic doors that allow glucose to enter your cells. In this way, insulin lowers the amount of glucose in your bloodstream and prevents it from reaching high levels. As your blood glucose level drops, so does the secretion of insulin from your pancreas. Your liver acts as a glucose storage and manufacturing center. When the level of insulin in your blood is high, such as after a meal, your liver stores extra glucose as glycogen in case your cells need it later. When your insulin levels are low, for example, when you haven’t eaten in a while, your liver releases the stored glucose into your bloodstream to keep your blood sugar level within a normal range. When you have diabetes If you have diabetes, this process doesn’t work properly. Instead of being transported into your cells, excess glucose builds up in your bloodstream, and eventually some of it is excreted in your urine. This usually occurs when your pancreas produces little or no insulin, or your cells don’t respond properly to insulin, or for both reasons. The medical term for this condition is diabetes mellitus (MEL-lih-tuhs). Mellitus is a Latin word meaning “honey sweet,” referring to the excess sugar in your blood and urine. Another form of diabetes, called diabetes insipidus (in-SIP-uh-dus), is a rare condition in which the kidneys are unable to conserve water, leading to increased urination and excessive thirst. Rather than an insulin problem, diabetes insipidus results from a different hormone disorder. In this book, the term diabetes refers only to diabetes mellitus.