If we look closer at the doctrine of the Word of Wisdom, it has something to do with our agency. Since agency is one of the precious gifts we received when we came here on earth, we need to take care of it. Substances that mess up our judgment are those included in the Word of Wisdom. They make us dependent upon them hence loosing our agency to these substances. If one feels that drinking Coke is becoming habitual and he cannot resist it, then he better stop drinking it. Actually, chocolates and Mountain Dew have a higher caffeine content than Coke. So if we don't drink Coke but love chocolates, then we are not better off. That's why it's called Word of Wisdom . . . we need to use our good judgment when taking in substances if it will become habitual and take away our agency.