Carbohydrates
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Carbohydrates
Summary:
Carbohydrates:
Carbohydrates are the main energy source for the human body. Chemically, carbohydrates are organic molecules in which carbon, hydrogen, and oxygen bond together in the ratio: C x (H2O)y, where x and y are whole numbers that differ depending on the specific carbohydrate to which we are referring. Animals (including humans) break down carbohydrates during the process of metabolism to release energy.
There are two major types of carbohydrates in foods: simple and complex.
Simple carbohydrates: These are also called simple sugars. Simple sugars are found in refined sugars, like the white sugar youd find in a sugar bowl.
Complex carbohydrates: These are also called starches. Starches include grain products, such as bread, crackers, pasta, and rice.
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Youve probably seen ads for low-carb foods and diets, but kids and adults need carbohydrates. Most foods contain carbohydrates, which the body breaks down into simple sugars – the major source of energy for the body.
When you eat carbohydrates, the body breaks them down into simple sugars. These sugars are absorbed into the bloodstream. As the sugar level raises in your body, the pancreas releases a hormone called insulin. Insulin is needed to move sugar from the blood into the cells, where the sugar can be used as a source of energy.
The carbohydrates in some foods (mostly those that contain a lot of simple sugars) cause the blood sugar level to rise more quickly than others. When this process goes fast – as with simple sugars – youre more likely to feel hungry again soon. When it occurs more slowly, as with a whole-grain food, youll be satisfied longer. These types of complex carbohydrates give you energy over a longer period of time.
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What are Carbohydrates?
Carbohydrates come from a wide array of foods – bread, beans, milk, popcorn, potatoes, cookies, spaghetti, corn, and cherry pie. They also come in a variety of forms. The most common and abundant are sugars, fibers, and starches. The basic building block of a carbohydrate is a sugar molecule, a simple union of carbon, hydrogen, and oxygen. Starches and fibers are essentially chains of sugar molecules. Some contains 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. Simple sugars were considered bad and complex carbohydrates good. The picture is much 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.
Fiber is an exception. It is put together in such a way that it cant be broken down into sugar molecules, and so passes through the body undigested.
Carbohydrates and the Glycemic Index
A new system for classifying carbohydrates calls into question many of the old assumptions about how carbohydrates affect health. This new system, known as the glycemic index, measures how fast and how far blood sugar rises after you eat a food that contains carbohydrates. (1).
White bread, for example, is converted almost immediately to blood sugar, causing it to spike rapidly. Its classified as having a high glycemic index. Brown rice, in contrast, is digested more slowly, causing a lower and gentler change in blood sugar. It has a low glycemic index.
The most comprehensive list of the glycemic index of foods was published in the July, 2002, issue of the American Journal of Clinical Nutrition (2). A searchable database maintained by the University of Sydney is available online.
Diets filled with high-glycemic-index foods, which cause quick and strong increases in blood sugar levels, have been linked to an increased risk for both diabetes (3, 4) and heart disease. (5, 6) On the other hand, lower GI foods have been shown to help control type 2 diabetes. (7)
One of the most important factors that determine a foods glycemic index is how highly processed its carbohydrates are. Processing carbohydrates removes the fiber-rich outer bran and the vitamin- and mineral-rich inner germ, leaving mostly the starchy endosperm. (See Fiber for more information on whole-grain foods.)
Other factors that influence how quickly the carbohydrates in food raise blood sugar include:
Fiber content. Fiber shields the starchy carbohydrates in food immediate and rapid attack by digestive enzymes. This slows the release of sugar molecules into the bloodstream.
Ripeness. Ripe fruits and vegetables tend to have more sugar than unripe ones, and so tend to have a higher glycemic index.
Type of starch. Starch comes in many different configurations. Some are easier to break into sugar molecules than others. The starch in potatoes, for example, is digested and absorbed into the bloodstream relatively quickly.
Fat content and acid content. The more fat or acid a food contains, the slower its carbohydrates are converted to sugar and absorbed into the bloodstream.
Physical form. Finely ground grain is more rapidly digested, and so has a higher glycemic index, than more coarsely ground grain.
All these elements lead to sometimes counterintuitive results. Some foods that contain complex carbohydrates, such as potatoes, quickly