First of all it's well known that a single session of exercise increases insulin sensitivity for hours and even days. 11,12
It's also known that a bout of resistance exercise results in a significant decrease in glycogen and that total energy content and CHO content are important in the resynthesis of muscle and liver glycogen.13
Glucose uptake and glycogen synthesis are enhanced in the presence of insulin following an acute exercise bout that lowers the muscle glycogen concentration and activates glycogen synthase. 14,15
Muscle glycogen concentration dictates much of this acute increase in insulin sensitivity after exercise.16 Therefore, an increased availability of dietary carbohydrate in the hours after exercise and the resultant increase in muscle glycogen resynthesis reverses the exercise-induced increase in insulin sensitivity.17
Along with glucose uptake, amino acid uptake and protein synthesis also increase. As well, the use of fatty acids as a primary fuel also rises after exercise since glycogen resynthesis takes priority to the use of glucose for aerobic energy.
However, as liver and muscle glycogen levels get replenished, insulin sensitivity decreases, as does amino acid uptake, protein synthesis and the use of fatty acids as a primary fuel.
By increasing insulin levels and not providing carbs you shunt your body's metabolism to the use of more fatty acids for energy while at the same time keeping muscle glycogen levels below saturation and amino acid influx and protein synthesis elevated for a prolonged period of time post exercise.
This increased capacity for glycogen synthesis, and everything that goes with it, can persist for several days if the muscle glycogen concentration is maintained below normal levels by carbohydrate restriction. By keeping carbs low and protein and energy high after training, you can increase protein synthesis over a prolonged period of time and get long term anabolic effect.18
As well, the type of protein used post exercise can have an effect on glycogen levels and thus the anabolic stimulus. For example it's been shown that a fast protein, such as whey protein, leads to increased glycogen levels over slow proteins such as casein.19
In the long run, the optimal protein for increasing protein synthesis, decreasing catabolism and increasing muscle accretion is a blend of slow and fast proteins, plus the addition of a few other useful ingredients.