When we ingest protein into are body it is broken down into amino acids. The human body cannot synthesize all amino acids so it's necessary to get them from an outside source, food. The broken down protein (amino acids) are then transfered into your blood stream and ingested by muscle cells, so those cells can sythesize those amino acids into protein (20 or more amino acids PEPTIDE) which inturn repairs the damaged muscle cells that are already made out of protein. So insulin doesn't carry protein. Free form amino acids are in your blood and are chemically signaled where you NEED them. So when you ingest protein, it isn't carried anywhere until it's broken down, then remade inside your muscle cell.