Post Workout Nutrients
During your workout your muscles use glucose (usable energy) and glycogen (stored energy) for energy. As such, there is a point at which blood glucose and glycogen levels get so low that intense exercise can't continue. There just isn't enough available energy for your muscles to use. Therefore, once you have finished your workout your body looks to muscle tissue for a source of energy.
What happens is that the hormone cortisol is secreted, this is your body's "stress" hormone and it has very catabolic effects (catabolic meaning the process of your body utilising vital protein and amino acids – the building blocks of protein – as energy). What cortisol does is eat up muscle tissue for protein and converts it into glucose. The net result is a loss of muscle tissue.
A post-workout protein shake is recommended as it will prevent this. It also allows insulin to be released. Whey protein is your best protein source at this time because it is absorbed quickly. It is recommended to have this within the first 15 - 30 minutes after you have completed your workout.
So the protein shake will fuel your muscles after your workout, but it is still essential to refuel your body.
As mentioned following a hard workout, your body is severely depleted of glucose and glycogen. Therefore after you workout is one of the few times simple carbs are recommend. This is critical because it starts the whole recovery and refuel process allowing for your body to function as required and not sacrifice the muscle growth process.
Normally, when we talk carb intake, it is best to consume complex carbs with a low Glycemic Index (GI) so as to not initiate an insulin spike. However, post-workout, the exact opposite is true. As it is critical to get the carbs to the muscle cells as fast as possible during this time, the consumption of simple carbs with a high GI is best.
The GI levels in food is a measure of how quickly a food raises blood sugar and hence insulin levels. It is recommended to consume these carbs within the 30 minutes - an hour after completing a workout. Keep in mind, this isn't an excuse to run for the mudcake. When I say simple carbs, I am still referring to unprocessed unrefined sugars. Simply consuming a banana will provide the required amount of simple carbs at this time.