*NOTE* One of the key things in being able to fast in a healthy matter is entering the state of ketosis - that is, switching your metabolism from burning carbohydrate to burning fat. *Considering most people have been burning carbohydrate their whole lives* this can make fasting a challenge. Upton Sinclair recommends doing quite long fasts - 12 days, but you may want to work your way up to longer fasts. Unless you are relatively keto adapted (or have experience with fasting of course), it's important that you take precautions while doing a fast. Fasting isn't inherently dangerous, *but diving into fasting when your body is in no way geared for it can be.* I recommend doing more research before doing longer fasts. "The Complete Guide to Fasting" (http://amzn.to/2tQjxXa) is a good book to start with.
As Tim Ferriss puts it: Please don't do anything stupid and kill yourself. It would make us both quite unhappy.
Just in case I should also say that of course you need to balance fasting with eating - You need to survive off of something. I have been doing intermittent fasting the past year (22 hours fasted, 2 hours eating - you can widen it to 16/8, which still provides great benefits) and will fast for a couple days every other month or so. Several other people have recommend a routine like this - Tim Ferriss recommends doing a 3 day fast once per month and a 7 day fast once per year.
Also make sure you're getting enough fat, protein, micronutrients and fiber to maintain a healthy weight and healthy body - *excessive* fasting can be very dangerous.
"The Obesity Code" by Dr. Jason Fung - http://amzn.to/2rXtalh
"The Fasting Cure" by Upton Sinclair - (If you google the title you can find the full book online)
"Tools of Titans" by Tim Ferriss - http://amzn.to/2rX6P7E
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