I personally believe a book like that could take many years. I have a great deal of knowledge in weight loss (over 100 lbs), studied to be a personal trainer, and technical school for leadership, so I could write a series on it. I sure wouldn't make it a hollywood cookie diet book, it would be purely motivation, organization, will power, self awareness, exercise and health knowledge, food knowledge, cooking, easy cooking tips/tidbits, so you could see how this could add up to 1500 pager! As long as you got your message along well, and the reader learned anough to change their life then it is ready. If it can't change a few lives yet, don't publish it. One good book from the heart is so much better than 4 little books.