God wants us to have a healthy clean body. Our bodies are not just for us! They are for God more. Through our bodies we are representing God, and we need to represent Him in the best way possible. 

It says in 1 Corinthians  6:19:
Your body is the temple of the Holy Ghost therefore glorify God in your body. 
And, it says in Deuteronomy 14:2
For thou art an holy people unto the LORD thy God, and the LORD hath chosen thee.

We need to keep ourselves healthy in order to glorify God to our best ability.