I read in a Christian book once how fasting for 3 days can help rid the system of any impurities and also help kick any bad habits. Dedicating your fast to a higher power was also recommended.

My father became a strict Vegan a few years ago for spiritual reasons. When he was explaining his reasons to me he said, "imagine climbing up a mountain with heavy bags and luggage...if you want to reach the top, wouldn't it help to drop the load?"

I guess so.

Humans have always been obsessed with purity. What you do with your body and what you put into it has always been considered important. And it is! If you eat better, you will feel better. Whether or not that's spiritual is up to you.