Diabetes Mellitus: An Overview

Diabetes: Prevention, Control, and Cure
by Seymour L. Alterman, M.D., Donald A. Kullman, M.D.

If you or someone you love has diabetes, you need this up-to-date, accessible, and comprehensive guide. Written by two experienced physicians, this trusted reference, now completely revised, shares everything you need to know to keep yourself in the best possible health. Discover

• the causes of diabetes - and how to prevent it and cure it
• the differences between type 1 and type 2 diabetes
• ways to reduce the risk of long-term complications
• the pros and cons of the insulin pump
• the facts on how diabetes can affect pregnancy
• how to manage diabetes-related impotence
• the proper diet, even when dining out and traveling
• alternative therapies and medical advances

Addressing hundreds of patient concerns, this essential guide will help you deal constructively with virtually every challenge a diabetic may encounter, so that you can live a full, productive, and meaningful life.

Chapter 1

Diabetes mellitus, or "diabetes" as it is commonly known, is a disorder of metabolism-the way our bodies use food to obtain energy. The most apparent disturbance in diabetes is with carbohydrate metabolism and is classically characterized by an elevated blood sugar and often the excretion of sugar in the urine. To understand diabetes, it is necessary to know how the body functions normally to convert food substances into energy. The human body may be thought of as a machine that requires "fuel" to function.

As we walk down the street, hit a baseball, or just take a breath, we expend energy. The body's fuel is obtained from the food we eat-carbohydrates (sugars and starches), proteins, and fats. Food must be digested-broken down in the gastrointestinal tract-before it can be absorbed. Complex carbohydrates such as those in vegetables and whole grains are composed of long-chain molecules that are broken down by the digestive enzymes into their simple sugar components. All the simple sugars are eventually converted into glucose, the body's main fuel, which is the form of sugar required by the body's cells for energy. Proteins are broken down by the digestive enzymes into their constituent amino acids. Fats are digested to fatty acids.

Your body is comprised of billions of cells, the smallest units of living matter. Each cell is surrounded by a cell membrane that protects the inside of the cell from its environment. For glucose to get into the cells, where it can be used, it must cross this protective barrier. The hormone insulin, manufactured by specialized cells in the pancreas,* called beta cells, is secreted directly into the bloodstream and transported throughout the body, where it plays a vital role in the conversion of glucose into usable energy by escorting it across cell membranes. It is the key that opens the cell door to allow glucose in.

Once taken up by the tissues, glucose is either metabolized (burned) to supply the energy for all body functions or is stored away for future use to be drawn upon later when needed.

The pancreas secretes a steady, constant basal amount of insulin.

In a healthy person, rising blood sugar levels after eating serve as a signal for the pancreatic beta cells to secrete insulin. The beta cells act like a tiny thermostat, constantly measuring the blood sugar and releasing precisely the right amount of insulin to ensure the correct balance between the blood glucose level and the quantity of insulin needed to metabolize the glucose and keep the blood sugar within a fairly narrow range. When blood glucose levels are high, insulin helps muscle and liver cells respond to the body's need to lower the blood sugar by removing glucose molecules from the blood and stringing them together to form long, complex molecules, called glycogen-an efficient form for glucose storage in the muscles and liver. Glucose that is not used by the body or exceeds its capacity for glycogen storage is converted into triglycerides-a storage form of fat.

The liver may be thought of as a food processing center. Insulin enables the liver to not only convert glucose into glycogen, but also to synthesize, from amino acids, proteins that the body needs for cell growth and repair. Any surplus amino acids are converted by the liver into glucose or glyco-

The pancreas is a flat abdominal organ situated in the posterior abdomen below and behind the stomach. It functions as though it were two organs. As a digestive organ, it secretes enzymes into the intestinal tract that help to break down food into constituents that the body can use. As an endocrine organ, it secretes insulin and other hormones into the bloodstream that regulate the metabolism of glucose, proteins, and fats. Normally, in non-diabetic persons, the pancreas can store approximately 200 units of insulin and it secretes about twenty-five to forty units daily to meet metabolic needs.

gen, depending on bodily needs. This process of manufacturing glucose from non-carbohydrate food sources, known as gluconeogenesis, helps the body function efficiently as it prevents any excess fuel from being wasted. Any carbohydrate or protein intake that exceeds the body's immediate energy needs and glycogen storage capacity is rapidly converted by the body-with an efficiency greater than any machine-into fat and stored away. Thus, any of the body's three sources of fuel-carbohydrates, protein, or fat-can end up as body fat. This explains why one gains weight, regardless of the type of food consumed, when the caloric content of the diet exceeds the caloric expenditure by the body.

After a full meal, the insulin-producing beta cells of the pancreas secrete adequate amounts of insulin to transport the glucose from the bloodstream into the cells, thereby keeping the blood sugar level from rising too high. Between meals-during the fasting state-blood sugar levels gradually decline, as do blood insulin levels. However, should the blood glucose level fall too low, the alpha cells, another group of specialized pancreatic cells, secrete a hormone, glucagon, which acts in an opposite or antagonistic manner to insulin. Glucagon raises the blood sugar by signaling the liver to break down its glycogen stores and release glucose into the bloodstream. Glucagon can also mobilize stored fat and muscle protein, which are then transformed by the liver into glucose.

Copyright © 2006 by Seymour L. Alterman, M.D.

About the Author

Seymour L. Alterman, M.D., F.A.C.P., is Clinical Professor of Medicine and Endocrinology at the University of Miami School of Medicine. He is certified by the American Board of Internal Medicine in Endocrinology and Metabolism.

Donald A. Kullman, M.D., has been practicing family medicine for more than forty years and is the editor of several medical books.