Carbohydrates are the ideal source of energy for the body, your body runs on carbs. During digestion, all carbs are broken down into glucose. Glucose is used by the cells in your body for energy and is the essential component of a carbohydrate. During an intense workout the body uses the glucose from the carbohydrates. When the body runs out of the glucose the next available source of energy is fat. The body will use fat as energy if you limit the amount of carbs it has to work with. When you limit the amount of carbohydrates in the body the production of insulin reduces. Insulin regulates the carbs and fat metabolism in the body, meaning your less likely to store fat. When you eat a carbohydrate it releases insulin into the body. The insulin regulates the nutrients in the bloodstream, storing it in either the muscle cells, liver or fat cells. When the insulin is released from the carbohydrate it stores the glucose and amino acids into the muscles. After training for extended period of time, the bigger the muscles you have the more glycogen and protein you will be able to store. Weight training produces bigger muscles which allows more nutrients to be store in the muscle tissue rather than the fatty tissue, and your muscles are more receptive to insulin. Ideally the best time to carb up is in the morning or right after a workout, your muscle tissues crave nutrients right after a workout. Balancing the intake of complex carbs(starches) and simple carbs (sugars). Vegetables are the best carbohydrate of them all because of the fiber, antioxidants, and protein enzymes. Eating oatmeal in the morning before a workout and a banana(in a protein shake) after a workout is an example of a slow burning carb(oatmeal) and a fast acting carb(banana). The fast acting carb will provide nutrients into the body folioing a workout. Starting a low carb diet does have benefits, mainly loss fat tissue but your body will also start to use muscle tissue as energy which is counterproductive during any weight loss or training regimen. Just remember to pick the right carbs and limit the simple carbs. All fruits and vegetables are ideal for muscle gain(sweet potatoes,oatmeal, beans). Berries and fibrous vegetables are ideal for fat loss.
Here is a helpful link for some healthy carbs http://www.buzzle.com/articles/complex-carbohydrates-list.html