Simple vs Complex Carbs
Carbohydrates can be dvided into two camps—simple carbs and complex carbs.
Simple carbohydrates
Simple carbohydrates are the ones found in candy bars, pastries, breads, crackers and soft drinks. Since simple carbohydrates usually contain a high percentage of undesirable fats (such as donuts and crackers) they are not the best source of energy. Most of these foods also contain a plethora of additives, which are not very "body-friendly", as well.
When a food has large amounts of unhealthy fat and sugar calories, which simple carbs usually do, then it is unlikely to have much value in the way of vitamins, minerals, or fiber. That is why these are called "empty calories."
However, some foods with high sugar content have plenty of minerals or vitamins. Bananas, oranges, apples, and raisins break down into fructose (natural fruit sugar) but are great carbohydrate sources.
Complex carbohydrates
Complex carbs take longer to digest and convert to glucose (sugars. They are then stored as glycogen (stored energy) in the muscles or liver, to be used for energy when needed during physical activity. Vegetables, grains, whole grain breads, and beans are valuable sources of complex carbohydrates.
When you train your body aerobically and consistently, your muscles will learn to store more energy. A "trained" muscle can store up to 50 per cent more glycogen than an "untrained" muscle—and the more glycogen the muscles can store, the longer they can perform without tiring.