My grandmother was fond of saying "there's more truth in fiction than in non-fiction" or words to that affect. For that reason, I'm happy to repeat what The Essene Gospel of Peace says about fasting - that we can undo seven years of sins through seven days of fast or a lifetime of sins in seven weeks. (http://essene.com/GospelOfPeace/peace1.html)
Using that scale of reckoning, a 17-year old could easily wipe the slate clean with a 21 day fast.
"Fat in the form of triglycerides in adipose tissue provides the largest and most efficient storage of body energy and constitutes 85 percent of all potentially available calories. In a 70-kg person basal caloric requirements could be met solely from fat stores for two to three months in the absence of any caloric intake."