(At the moment I am not on the Keto diet.)
I gather it takes a while before the body can be convinced to use ketones.
However, can that process be initiated at the start of a Ketogenic diet by a three day water fast?
If the body has no food for three days, it goes into ketosis right ? Boom, - you’re right there in 3 days.
Short answer: yes
Longer answer: it will be rough, and there’s really no reason to suffer and torture yourself. What are your goals/reasons for seeking ketosis?
I’ve done 3 days water fast before. And it is rough, but if you have the right mindset going into it , then you are prepared to accept it.
More energy because I have CFS, and elimination of Lyme disease. Plus losing a few pounds and having more mental energy.
I wouldn’t force it then. Just limit carbs to 20g or less a day, moderate protein scaled to your lean body mass, and eat fat to satiety. Following that will also generally get you into ketosis in a few days, but more importantly will get you on the path to being fat adapted. At that point, fasting (if you choose to) becomes very easy and almost natural.
Forcing fasting without being fat adapted really jus equals calorie restriction. You’ll be in ketosis, but it’s tough because you body is still looking for carbs and will end up adjusting your metabolism because it’s not getting the energy it wants.
Thats helpful. I thought it took a few weeks to get your body into ketosis, and thats why fasting appealed. I wouldn’t do fasting if I could avoid it, because its not the easiest thing for me to do. Its rough.
In the past when I’ve water fasted > 3days I have noticed a mental clarity that is unusually nice.
Obviously being physically tired offsets the niceness.
But, this is what gives me hope that my bosy can use ketones for mental energy.
Ketosis happens pretty quick, but it often takes a couple weeks to get through carb withdrawal (aka keto flu). Stick to it though, it will be worth it.
It could get you into ketosis yes, but wouldn’t get you keto adapated and they’re different things. Also, a fast of that length before keto adaptation wouldnt be a nice experience. Why not just eat keto and go from there? Only takes a few days to get into ketosis naturally, the more active you are the quicker your body uses up the stored glycogen and once that’s done it be producing ketones.
Yes, boom. But LindsaySue raises an extreeeeemly important point. 3 days is a bunch running on just water…IF… you are still a sugar burner, and MOST ESPECIALLY…if you are a fasting newbie.
Even if a beginner can pull it off, you may feel so deprived afterward, that you will BREAKfast very poorly. (Ask me how I know) 
Then, you could wind up being “turned off” to fasting. That’s bad juju my friend.
Get yourself fully fat adapted by the normal method. That’s my advice. Oh, you’ll be in KETOsis, trust me. Then fasting is easier, not the other way around.
Fasting is a skill that requires a little practice. I blew one badly, just about a week ago. And that’s with lots of experience over many years.
Beginning a 3 day fast without being fat adapted will not be fun.
Eat keto for a few weeks to get a hang of the this way of eating and get fat adapted. Then, when you fast, it will be easier, and when you get off your fast, you will know what to eat.
What’s your motivation for wanting to start this diet by the way?
I did what you are suggesting. I started my keto with a 3-day water fast (Sept 2017). It put me into ketosis and I stayed in ketosis until I got bumped out on Thanksgiving Day. Even though it seemed to work for me, if I could do it over again, I would pass on the initial fast and just start eating keto.