During your training session, your muscles use up the glucose (readily available energy) and glycogen (stored energy). Once your body has used up all of the glucose and glycogen it has, it begins to secret the hormone cortisol (Stress Hormone). Cortisol has a very catabolic (break down) effect, and it essentially eats up your muscle tissue to break it down into protein and ultimately glucose.
This process is called gluconeogenesis, it produces glucose in your liver from the amino acids from your broken down muscle tissue. The net result is muscle loss.
Taking in a high quality whey protein source along with high glycemic (simple) carbohydrates immediately following your training session will prevent gluconeogenesis and also release insulin. Insulin is an anabolic (building) hormone needed to help build new muscle tissue.
How many carbs and protein should I be consuming after I train?
This answer will vary greatly by several factors. It will be based on your fitness goals, sex, age, weight, height, training schedule, etc. (If you want to get your exact numbers, click here to sign up for the most epic nutritional coaching program there ever way).
But what we do know is that you should be taking in approximately 30%-50% of your recommended carb load immediately after you work out. As for protein, you should be consuming a 2:1 ratio of carbs and protein. So if you are consuming 80g of carbs post workout, you should also be taking in 40g of protein. The consumption of Protein and Carbs at this ratio speeds up the absorption rate of the protein and to start the recovery and repair process immediately.
What kind of carbs and Protein should I be taking?