Timing is key when it comes to muscle glycogen replenishment. Muscle cells are most sensitive to insulin two hours after exercise. Assuming enough carbohydrates are available, elevated blood-insulin levels after exercise expedite the transport of glucose into muscle cells, where it is converted to glycogen. After two hours, muscle cells become more resistant to insulin and remain so for several hours. Because insulin plays such a vital role in replenishing glycogen stores after exercise, researchers have focused on enhancing insulin release during recovery.
Studies show that protein, when combined with carbohydrates, almost doubles the insulin response.
So it seems logical to include protein in a recovery sports drink. However, more is less in this case. Protein also stimulates a peptide called cholecystokinin, or CCK, which slows stomach emptying. Too much protein, therefore, slows fluid and electrolyte replenishment during recovery because fluids must exit the stomach before they can enter the intestines and be absorbed into the bloodstream. The challenge, then, is how to gain the insulin-increasing benefits of supplemental protein while avoiding its effect on stomach emptying.