My longest was 14days and I just jump into it witout preparing. Fasting is a mindset to me. And eating properly b4 I think helps ppl getting use to eating less. I did get great results from 14days but ended by fast horribly. So its trial and error but this time I have it planned out and will break my fast properly. I take my fast day by day too. Mine r broken up in 5day blocks and every 5days I give my self a reward(non-food related) for completing those days