
Pick your carbs wisely. Most of your carb intake should be from complex carbohydrates. Complex carbs are usually from unprocessed, unrefined, whole grains. So instead of white rice, eat brown rice. Instead of white bread each whole grain bread, etc. They take longer for your body to digest and because of this complex carbs will stay with you and provide energy for the long haul. Most of the early part of the carb-loading phase before the race will consist of eating complex carbs.
Simple carbohydrates are food products that are made of processed and/or refined grains. Because they have been processed and refined, they are digested very quickly and provide quick energy. Sugary soft drinks, white rice, sugar, candy, and fruit are examples of simple carbs. Don't avoid simple carbs completely, however. For example fruits are simple carbs, but they are nutrient dense foods that provide many different vitamins as well as fiber. Simple carbs, because they are processed so quickly, do raise the blood sugar levels really quickly. That's why when you eat a candy bar you feel a quick boost of energy, but then soon after crash. Simple carbs tend to have a high GI (a rating using the Glycemic Index) and complex carbohydrates tend to have a lower GI. Foods considered high are 70+ on the GI scale, 56-69 are considered medium, and under 55 are considered low. [Click here] to find out more about the Glycemic Index.

As a runner, eating foods with a lower GI will provide you a better source of energy for the long haul. But simple carbs do have their place. Eating simple carbs shortly before a race can provide quick energy that will be used and if you have stock up prior to the race on complex carbs, you shouldn't feel that crash. Also during the race, using gels and sports drinks (which usually contain a combination of simple and complex carbs) and be used quickly by the body and provide that needed energy later on in the race when your glycogen stores begin to get depleted.
Note: If you are diabetic or have other health concerns, consult with your doctor before making any dietary changes.