Carbohydrates

The word carbohydrate comes from the Latin carbo for carbon, and hydras, which refers to the combining with water. As a group, carbohydrates represent the body's most important source of energy. There are three basic types; simple carbohydrates, complex carbohydrates, and fiber.

Simple and Sweet
The most important carbohydrate is glucose (also called blood sugar). Glucose is the body's basic fuel: it's the preferred fuel of the brain and nervous system, and the only fuel that the red blood cells can use. Indeed, there are entire body systems dedicated specifically to maintaining the level of glucose in the blood.

Glucose is referred to as a single sugar because it exists as individual, unattached units. Other common single sugars in our diet include fructose, also called fruit sugar, and galactose.

Simple carbohydrates can also be double sugars, which are two single sugars connected to one another. The most common of these is sucrose, or table sugar (glucose and fructose); lactose, or milk sugar (glucose and galactose); and maltose (glucose and glucose), which is found in grains and malt beverages such as beer. What simple carbohydrates share is sweetness; they stimulate the sweet taste receptors on the tongue.

It's All in the Build
Although glucose is a "single" sugar, it serves as the building block for the complex carbohydrates, which are found in grains, legumes, and potatoes. These complex carbohydrates, or starches, consist of hundreds to thousands of glucose units connected to each other in straight-line or branched formations. They are too large to be absorbed through the wall of the digestive tract, so the body releases a set of enzymes designed to break the starch apart, piece by glucose piece.

Cellulose is a complex carbohydrate that is found in hay and wood pulp as well as many vegetables. It is also made from glucose. The big difference, though, between a meal of mashed potatoes and one of mashed wood is that the body lacks the enzymes needed to separate the complex of glucose units of cellulose. As a result, the starch gets digested and absorbed, while the cellulose passes through the system unabsorbed. Because the body cannot digest cellulose, this complex carbohydrate is classified as a dietary fiber.

The Fuel with Something Extra
Normally, muscles require oxygen from the bloodstream when they work. This is why our breathing rate picks up during physical activity. Carbohydrates, though, are exceptional in that they're an anaerobic fuel (an = without; aerobic = requiring oxygen). There's a small amount of stored carbohydrate, called glycogen, in the muscles and liver, and the body relies on this fuel to meet special demands. It's this fuel and the anaerobic ability of carbohydrates that enable us to dash across a room and grab a falling child or sprint down the street to catch a bus. This carbohydrate provides a vital source of energy that keeps the muscles working until the lungs gear up to provide the needed oxygen.

Focus on the Complex
When thinking about carbohydrates in your diet, focus on the complex rather than the simple sugars. Why should we do that, if all carbohydrates end up as glucose? The answer is in the nutrient company the different carbohydrates keep. Except for fruits, foods high in simple sugars tend to be high-calorie and often high-fat processed foods, where intense flavor or a sweet taste is the main offering. In contrast, complex carbohydrates are generally found in grains, vegetables, and legumes – whole foods with a wide array of valuable nutrients and fiber.

More on: Nutritional Resources for Families

Excerpted from:

From The Nutrition Doctor's A-to-Z Food Counter. Copyright © Ed Blonz, 1999. Used by arrangement with NAL Signet, a member of Penguin Group (USA) Inc.

To order this book visit amazon.com.