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 :)