[Cro_on]

woow, other comment recommending fifteen day fast is a) dangerous and b) doesn't answer your question??

i fast twice per week for ~30 hours and drink copious amounts of tea and coffee. but intermittent fasting also works, the really important information is that ketosis can begin after as little as 12 hours, so basically fast for a minimum 14 hours if you want any effect at all, and everything after that is bonus. no extras in your coffees btw, though a splash of milk / coconut oil in your breakfast coffee is acceptable :)

[PoachedSausage]

Where is the evidence that a 15 day fast is dangerous?

[Cro_on]

i think it would be premature to assume that it had universality in the same way as something like intermittent fasting.

the possibly dangerous part is recommending that particular part of the book in response to a query asking for how long one needs to fast to feel the effects.