Between 45% and 75% of the body weight of a typical human being consists of water. Other components of the human body include proteins, fats, carbohydrates, various minerals and various gases. In the 1950s, researchers conducted experiments which involved feeding subjects with radioactive atoms and then observing those atoms as they moved throughout the body. They found that new atoms continually replaced old ones, and that 98% of all the atoms in a human body were replaced each year.
This creates an interesting philosophical issue. I still seem to be the same person I was 12 months ago, but in fact 98% of the atoms which make up my body are different from the atoms which made up my body last year. Clearly the atoms which constitute my body cannot define who I am. I am more like an enduring idea, and the atoms which are in my body are simply temporary servants to that enduring idea.
In Mark chapter 7, Jesus said, “There is nothing from outside a person that pollutes the person when ingested. The things which come out of the person are the things which pollute the person.” Anything which a person eats will work its way through the body and out again, in a fairly short period of time. The atoms which make up the body don’t define who the person really is. It is the things which a person says and does which define who the person is, and they are the things which cause real pollution.