About 72% of the human body is H2O (liquid water). Every ~16 days nearly 100% of the water is exchanged in a healthy body. Heavy elements like carbon, sodium and potassium take occupancy far longer perhaps 8 months - 11 months. For example the calcium and phosphorus in bones are replaced in a dynamic crystal growth / dissolving process that will ultimately replace all bones in your body.
Other larger organs' atomic replacement can be estimated:
• The lining in stomach and intestine every 4 days
• The Gums are replaced every 2 weeks
• The Skin replaced every 4 weeks
• The Liver replaced every 6 weeks
• The Lining of blood vessels replaced every 6 months
• The Heart replaced every 6 months
• The Surface cells of digestion, top layer cells in the digestion process from our mouth through our large bowel are replaced every 5 minutes
This data was first pointed out by Dr. Paul C. Aebersold in 1953 in a landmark paper he presented to the Smithsonian Institute, “Radioisotopes - New keys to knowledge”
In about a year every atom in your body would have been exchanged. Not a single atom in your body resides there forever and there is a 100% chance that 1000s of other humans through history held some of the same atoms that you currently hold in your body.
To be sure this data is confounding and seems to defy logic. However the Radioisotope data as far back as 1953 is quite conclusive. The data is not based on urban legend or assumptions yet certainly seems to feel this way.
Just as fascinating, is the fact that about 30% of your body, by weight, is not even “you” (cells without human DNA/RNA), it is a cooperative arrangement of bacteria, viruses, parasites and other welcomed or sometimes unwelcome guests. In fact, just in the case of bacteria, there are 10 times more bacteria cells then human cells in your body.
This leaves one with perhaps a very large philosophical question: " If every atom in our body is replaced each year, who are we if we are not our atoms and we are not our cells? "