“Or do you not know that your body is a temple of the Holy Spirit who is in you, whom you have from God, and that you are not your own? For you have been bought with a price: therefore glorify God in your body.” (1 Corinthians 6:19-20 NASB)
I don’t think God is simply saying, “Keep healthy, stay in shape.” That is important and becomes more so as we age, but we are discussing the spiritual realm. A temple for the Holy Spirit. Our body was purchased at the cross. No longer held captive by Satan, through sin, we begin in the spirit as slaves to righteousness. The Holy Spirits temple is meant to glorify God, and as we do the slave becomes a friend.
“You are My friends if you do what I command you. No longer do I call you slaves, for the slave does not know what his master is doing; but I have called you friends, for all things that I have heard from My Father I have made known to you. You did not choose Me but I chose you, and appointed you that you would go and bear fruit, and that your fruit would remain, so that whatever you ask of the Father in My name He may give to you.” (John 15:14-16 NASB)