I'm certainly no expert. But food and fasting are but one small piece of the pie. The main component by far is thoughts/feelings/attitude.
These effect a person hugely. If you have good wholesome positive clean healthy thoughts, one would not indulge in harmful foods or binge, or emotionally eat. You can be a fantastic person but have bad thoughts: jealousy, worry, grief, anxiety, stress, poor coping, toxic relationships, promiscuity, not respecting ones body.... And and and... Even being too involved in technology/social media, there is so much that effects it. Thoughts become feelings and feelings become attitudes. Healing is first in the heart and mind #1.
Having said that: I have pretty much alternative day fasted since 2011 - unless sick, traveling or special even -which are all rare. Except when I have to re-feed after fasting.... I've done maybe two dozen 3, 10,12 days fasts, and two 28&29 day fasts.
I feel the best on 10 day fasts, myself personally. I think because I fast so regularly more than 14 days is pretty taxing for myself personally. For others 30 days is good, perhaps as they don't fast as regularly. But it all comes done to what you eat after. You can stuff it up and it's like you neeeever even fasted... And then you have to re do all the work you undid.
Prior to 2010 I was into some serious junk food. I stayed skinny and seemed healthy so I thought it was ok. Since then I learned and changed pretty hardcore. Breakfast was a row of a block of chocolate, morning tea was redbull and coffee - both, lunch was whatever restaurant or cafe I fancied and dinner was nothing, toast, or nachos. If I had exams or assignments it was straight coffee only by the litre for days and days until it was finished then I'd celebrate with my favourite foods. My worst were the three c's: coffee, cheese, and chocolate. Today I don't have any of those.
I do note that the more I fast, the greater sensitivities I have to food. I figure it's my body calibrating and refining and being more discerning as to what fuel it prefers. I hate eating every single day it feels bluuurrr every second day feels better... If I must eat consecutive days I eat only at midday and avoid other times.
Additionally pineapple fasting in excess of 10 days shrunk a cyst I had considerably.
But this is only what worked for me... And it's more important to keep a clean heart and clean thoughts. Soul searching is by far better, forgiving and seeking forgiveness and being shy to do wrong is better. Infinitly !