Diabetes is a disease of the substance sugar, but is really about energy. In the final analysis, diabetes is a disease of poor energy metabolism. It is manifest in problems with sugar, the crucial fuel, and insulin, the crucial energy hormone. To understand diabetes, we need to understand biological energy: where it comes from, what it is, and how it works.
Life is work and work is energy. Energy for life comes from the same source as a flame. In a flame, oxygen in the air combines with carbon in candle wax to make carbon dioxide and water. In our body, oxygen also combines with carbon. The difference between a candle and a human is in the violence of the method. The human metabolism is carried out at a lower temperature and makes better use of its energy.
Energy for life is found in many forms. People with diabetes mostly worry about carbohydrate, which means sugar. Some forms of energy last longer than sugar, while others don’t last as long. For example, carbohydrate, in the form of glycogen, stores energy from as short as one hour, to as many as several days. While carbohydrate in the form of glucose, can store energy from minutes to hours. Conversely, fats are very stable, and can be stored for days to weeks to be used later.
All of these forms exchange their free energy in a process called metabolism. Glucose sugar is the fulcrum of energy metabolism. Some tissues like the brain rely almost exclusively on sugar; all tissues use it to a certain extent. It is the perfect fuel: easy and quick to burn, easy to transport. Glucose has a major drawback, though. It reacts with proteins and literally gums them up. Our bodies solution to this problem is to use enormous resources to keep the amount of glucose in the blood close to constant. The difficulty of this task is immense, but the reward is great. At 95 mg. of glucose per dl. of blood, there is enough sugar to fuel everything that wants fueling, and damage to the proteins in the body is manageable. When blood glucose rises above 180 mg/dl, damage to the proteins of the body occur, and we have a condition called diabetes.
Diabetes has two causes, both related to insulin. Insulin is a beautiful, simple protein, but has a complicated itinerary through the body. It is made in the islets of Langerhans in the pancreas. It first goes to the liver, where it spends five to fifteen minutes; then it goes to the rest of the body, where it affects all tissues, especially the muscle and fat cells. More on this fascinating part of metabolism will appear in future columns.