Blood Sugar and Insulin The Basics

You need to know a little about normal metabolism to understand how so many of us are developing prediabetes and then diabetes. Metabolism represents the body's processes that direct energy into storage, such as in fat, or into fueling normal growth, development, and physical activity. Carbohydrates (including complex starches and simple sugars), fat, and protein are the three nutrient groups in our diet that provide the energy and building blocks for metabolism and growth. Carbohydrates and fat provide most of the energy to keep our body's machinery working, including our muscles for locomotion and our vital organs such as brain, liver, heart, lungs, and kidneys.

Carbohydrates are broken down in the intestine into smaller sugars that can be absorbed into the circulation. (See Figure 1.1.) Sugar or glucose is then transported from the blood across the cell wall and into the cell where it is broken down further, providing a major source of energy. Alternatively, sugar may be stored in the liver or muscle as glycogen, which is a complex carbohydrate that serves as an energy reservoir in times of energy need. Fatty acids, a breakdown product of dietary fat, are the other major sources of energy. Like glucose, they may provide instant energy for cells or may be stored as fat for later energy release.

For sugar to gain entry to most cells, it must be carried across the cell wall by glucose transporters. This is where insulin first comes into play.

Insulin is a hormone, which means it is a protein that is made and secreted by specialized cells and then circulates in the bloodstream and affects other organs and their function. Insulin is made

[FIGURE 1.1 Digestion

Food is broken into its building blocks, simple sugars from carbohydrates, fatty acids from fat, and amino acids from proteins, and then absorbed into the blood from the small intestine (1). The breakdown of the food groups is aided by chemicals secreted by the pancreas (2). The pancreas also releases insulin, which helps transport sugar, fatty acids, and amino acids into muscle, fat, and the liver (3).

in the pancreas, an organ located in the back of the abdomen. Most of the pancreas makes digestive chemicals that help break down nutrients from your food so that they can be absorbed in the intestine. The pancreas also contains small clusters of cells called "islets." Although different types of specialized cells are in the islets, the most important are the beta cells that make insulin.

These beta cells can sense the level of sugar in the blood, for example after a meal. When blood-sugar level starts to rise, the beta cells make and secrete insulin, which increases the transport of sugar into the cells and keeps the blood-sugar level from rising too high. But the work of insulin has only just started at that

FIGURE 1.2 Normal Glucose Absorption

When insulin is present in adequate amounts, it binds to specialized receptors (like a key fitting into a lock). The receptor-insulin complex results in glucose transporters moving from inside the cell to the cell surface where it attaches to a glucose molecule and moves it from the bloodstream inside the cell.

When insulin is present in adequate amounts, it binds to specialized receptors (like a key fitting into a lock). The receptor-insulin complex results in glucose transporters moving from inside the cell to the cell surface where it attaches to a glucose molecule and moves it from the bloodstream inside the cell.

point. Insulin also stimulates the processes in the cells that direct the storage of sugar as glycogen, the storage of fatty acids as fat, and the use of amino acids, the building blocks of proteins. In addition, insulin prevents protein breakdown, fat breakdown, and glycogen breakdown. Therefore, insulin directs the storage of energy and stimulates the building of tissue and growth. (See Figure 1.2.)

When blood-sugar levels fall, insulin production and secretion shut down and all of the processes are reversed: sugar is released from the storage depot instead of stored in muscle and liver; fat is broken down and fatty acids released; and proteins are broken down rather than synthesized. Insulin is like a traffic cop, directing nutrients into storage and growth. When insulin levels are low, the traffic moves in the opposite direction with energy released from its storage sites.

This is what happens in a healthy person. When something disrupts any part of this finely tuned system, there is trouble. Diabetes is by far the most common disease of abnormal metabolism.

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