What Are Carbohydrates?

Carbohydrates are found in a wide array of foods—bread, beans, milk, popcorn, potatoes, cookies, spaghetti, soft drinks, corn, and cherry pie. They also come in a variety of forms. The most common and abundant forms are sugars, fibers, and starches.

The basic building block of every carbohydrate is a sugar molecule, a simple union of carbon, hydrogen, and oxygen. Starches and fibers are essentially chains of sugar molecules. Some contain hundreds of sugars. Some chains are straight, others branch wildly.

Carbohydrates were once grouped into two main categories. Simple carbohydrates included sugars such as fruit sugar (fructose), corn or grape sugar (dextrose or glucose), and table sugar (sucrose). Complex carbohydrates included everything made of three or more linked sugars. Complex carbohydrates were thought to be the healthiest to eat, while simple carbohydrates weren't so great. It turns out that the picture is more complicated than that.

The digestive system handles all carbohydrates in much the same way—it breaks them down (or tries to break them down) into single sugar molecules, since only these are small enough to cross into the bloodstream. It also converts most digestible carbohydrates into glucose (also known as blood sugar), because cells are designed to use this as a universal energy source.

How much fiber do we need?

Adults need at least 20 to 30 grams of fiber per day for good health. But most Americans get only about 15 grams a day. Fiber is an exception. It is put together in such a way that it can't be broken down into sugar molecules, and so it passes through the body undigested. Fiber comes in two varieties: soluble fiber dissolves in water, while insoluble fiber does not.

Although neither type nourishes the body, they promote health in many ways. Soluble fiber binds to fatty substances in the intestines and carries them out as a waste, thus lowering low-density lipoprotein (LDL, or bad cholesterol). It also helps regulate the body's use of sugars, helping to keep hunger and blood sugar in check. Insoluble fiber helps push food through the intestinal tract, promoting regularity and helping prevent constipation.

Carbohydrates and the Glycemic Index

Dividing carbohydrates into simple and complex makes sense on a chemical level. But it doesn't do much to explain what happens to different kinds of carbohydrates inside the body. For example, the starch in white bread and French-fried potatoes clearly qualifies as a complex carbohydrate. Yet the body converts this starch to blood sugar nearly as fast as it processes pure glucose. Fructose (fruit sugar) is a simple carbohydrate, but it has a minimal effect on blood sugar.

A new system, called the glycemic index, aims to classify carbohydrates based on how quickly and how high they boost blood sugar compared to pure glucose. Foods with a high glycemic index, like white bread, cause rapid spikes in blood sugar. Foods with a low glycemic index, like whole oats, are digested more slowly, causing a lower and gentler change in blood sugar. Foods with a score of 70 or higher are defined as having a high glycemic index; those with a score of 55 or below have a low glycemic index.

Good Carbs, not No Carbs

Some popular diets treat carbohydrates as if they are evil, the root of all body fat and excess weight. That was certainly true for the original Atkins diet, which popularized the no-carb approach to dieting. And there is some evidence that a low-carbohydrate diet may help people lose weight more quickly than a low-fat diet, although so far, that evidence is short term.

Adding Good Carbohydrates

For optimal health, get your grains intact from foods such as whole wheat bread, brown rice, whole grain pasta, and other possibly unfamiliar grains like quinoa, whole oats, and bulgur. Not only will these foods help protect you against a range of chronic diseases; they can also please your palate and your eyes.

Until recently, you could only get whole-grain products in organic or non-traditional stores. Today they are popping up in more and more mainstream grocery stores. Here are some suggestions for adding more good carbohydrates to your diet:

• Start the day with whole grains. If you're partial to hot cereals, try old-fashioned or steel-cut oats. If you're a cold cereal person, look for one that lists whole wheat, whole oats, or other whole grain first on the ingredient list.
• Use whole grain breads for lunch or snacks. Check the label to make sure that whole wheat or another whole grain is the first ingredient listed.
• Bag the potatoes. Instead, try brown rice or even "newer" grains like bulgur, wheat berries, millet, or hulled barley with your dinner.
• Pick up some whole wheat pasta. If the whole grain products are too chewy for you, look for those that are made with half whole-wheat flour and half white flour. 
• Bring on the beans. Beans are an excellent source of slowly digested carbohydrates as well as a great source of protein.

Excerpts an article from the Harvard School of Public Health
http://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/carbohydrates-full-story/index.html    
Copyright 2009