Carbohydrates are your body's primary source for energy. Carbohydrates are comprised of sugars, starches, and cellulose. Your body must break down carbs in order to turn them into glucose (commonly referred to as blood sugar). The reason too many of the wrong kind of carbs aren't good for you is that your body can convert them into body fat to use (or not use) later.
Not All Carbs are Created EqualThere are two different types of carbohydrates. Discerning among the two is important, because their impact on your body differ significantly. Simple carbohydrates (sugar) like table sugar, honey, candy, and the like, are digested quickly and give your body an energy surge.
An example of the effects of simple carbs is one we can all identify with. You know the "buzz" you get from eating a candy bar? That's the carbs at work. I'm sure you know the crash you feel soon after, too. You have some energy for a while and then you veg out. That's a simple carb for you, alright; they leave you high and dry. You'll feel hungrier much faster after eating simple carbs than you do after eating protein or complex carbs. That's why after you eat toasted white bread for breakfast, you're ravenous before noon.
Kinder, Gentler Carbs
Then there are the "good guys" of the carbohydrate world, complex carbohydrates. Complex carbohydrates are comprised of starchy and fiber-rich foods. They are processed by your digestive system much more slowly than simple carbs are. Examples of complex carbohydrate foods are legumes, fruits, grains, and other vegetables; starchy foods include potatoes, wheat, rice, and corn.
Most complex carbs are high in nutrient value; they contain plenty of vitamins, minerals, and fiber. Complex carbs are the "best bargains for your calorie buck." They help you feel more satiated (you feel fuller longer) than simple carbs. This is because high fiber foods are absorbed at a slower rate than other foods. In general, complex carbs are far better for you than simple ones.
Carbs 'Got Work to Do!
Both complex and simple carbs supply glucose to your muscles. Once the carbs are "manufactured" as fuel, a few things can happen. The fuel is used right away for your body to perform its regular functions or to exercise, it is stored as potential energy, or, if your cells don't require anymore glycogen, they convert into fat. (Incidentally, this conversion to fat is the basis behind the many popular carb-reducing diets.)