What's the difference between these two strategies and which would/may be more beneficial to health?

A lot of people talk about doing a daily 14-16 hour fast, such as no food between 8pm and 12 noon the next day.

Some people advocate a "5:2" fast, eat regularly 5 days, but fast 24 hours 2x a week, or eat a very low amount of calories, like 500-800.

The main idea behind this is to keep weight and main markers of health in check, yes? Prevent illness, etc.

Then you have people who do long fasts of a week or more consuming only water. This seems scary and basically like starvation to me. I've heard of people dropping dead from this too or it causing deleterious effects on the body. Other than losing weight if your severely overweight, is there any reason to fast for say a week or more? And how often/why would one do this?

There is so much different advice out there it's confusing as fuck.

(http://www.autoadmit.com/thread.php?thread_id=3987251&forum_id=2#36132999)

if youre just overweight than 2 one day fasts or a 2 day fast a week is credited

If youre average weight then a one day a week fast is fine

(http://www.autoadmit.com/thread.php?thread_id=3987251&forum_id=2#36133249)