God gives us our bodies to hold the light and power that our spirits have--to be filled with love and intelligence. For this purpose, our bodies have certain natural desires--desires for love, desires for nourishment, and so forth. However, Satan tempts us to give in to these desires in ways that contradict God's laws.
Addictions and sins are usually motivated by fundamentally good things that are twisted to an improper use. That is why almost everyone will inherit a kingdom of glory, as shown to Joseph Smith (D&C 76). For example, food is fundamentally good and important. However, some obsess over food to the point of eating too much, too little, or too unhealthfully. We sometimes lose sight of the real reason God gave us food--for health and for moderate joy--and eat to forget our troubles. Most sins are not because we are fundamentally evil, but because we allow a lesser good to distract from God. Elder Maxwell stated, "On the two great commandments, Jesus declared emphatically, everything else hangs, not vice versa (see Matthew 22:40). The first commandment is not suspended just because of our vigorous pursuit of a lesser good, for we do not worship a lesser god" (Neal A. Maxwell, “Consecrate Thy Performance,” Ensign, Dec 2008, 26–30).
I've been reading out of a book, Willpower Is Not Enough. It makes the wonderful point that to change, we don't just gain more willpower. Instead, we redirect our natural, fundamental desires. A desire for love and closeness can easily be misinterpreted as a desire for romance or sex. A desire for good, wholesome food can easily lead us to binge on M&M's. The addiction never actually fulfills the desire, and so we go on and on. If you have ever eaten half a package of Oreos, I'm talking to you! (Yes, I have.) It's not because we are evil binge-eaters. I was just hungry, and Oreos were easier than making healthy food. Obviously, eating sweets just doesn't work as well.
Anyway, good luck to everyone who reads this--most importantly myself--in their quest to sanctify their minds and bodies. The Holy Ghost is the single most powerful tool in this quest. It can change who we are. That is how the Atonement reaches us--the Savior's sacrifice authorizes the Holy Ghost to help us.