Hello! I’m a serial lurker on these forums and not one to post often. I’m just breaking my 42 hour fast. Last meal was 6pm on Wednesday. I felt good during the fast (this is my third fast since going on the ketogenic diet). I had black coffee, herbal tea, lots of water (with added salt at times). This morning (at the 36 hr mark) I drank my coffee with a teaspoon of coconut oil and teaspoon of heavy cream. So, technically I really only fasted for 36 hours. Then at noon, I had 1 oz NY strip steak, 1/4 c broccoli, two hard boiled eggs, a 1 oz piece of full fat cheese, and a keto choc chip cookie. Now I have a raging headache. Anyone else experience this? I’ve never had this in my prior fasts. Although, this is my first fast I went over 24hrs. I can understand getting an headache “during” the fast but not when I start eating again.
42 Hour Fast (Headache after eating/breaking the fast)
I’ll let others with more experience respond specifically. Maybe you just ate too much too soon. 36 hours doesn’t seem like a long time on a fast, but your mileage may vary.
36 hours may not seem long but I’ve only been on keto for 2.5 weeks. I’m working my way up to longer fasts.
From your preferences: When I began Keto: February, 2019.
If you’ve just begun keto (2.5 weeks) then fasting is probably not yet a good idea. It’s better to wait a few months until you are more fat adapted. But as I said, I’ll let others with more experience comment on that specifically.
I still think, if the headache is related to the fast, you probably ate too much too soon. If you did not experience this previously with similar fasting times, things change. Or maybe the headache is not related to the fast.
I’ve been fat adapted after 7 days of the ketogenic diet. My blood test result showed 1.6 ketone and 80 blood sugar. I’ve been tracking my foods, testing my blood…and according to Dr Fungs book, The Complete Guide to Fasting, you can start fasting at anytime. Of course he doesn’t recommend long fasts as first but anything from 12-48 hour fasts are safe.
FYI - I went off Keto in June of last year and haven’t started back up until 2.5 weeks ago.
I have no idea about the reasons of headache but of course you can fast any time if you feel ready.
I am especially bad with recommendation and rules so my first fast happened on high-carb and it was 120 hours long. It was fine, maybe I should have supplemented sodium on the last days but it was fun 
But it was me, that single time. People are different and it’s usually better to do things gradually.
A 36-42 hour fast doesn’t sound long at all but maybe you are a tad more sensitive or your food choices weren’t perfect or it’s something unrelated, my headaches have zillion possible reasons.
You will get experience when you have more fast, I doubt it can be solved easily but maybe the experienced ones will have ideas. I rarely go over 26 hours and never had problems with the slightly longer ones.
Don’t kid yourself. You’ve been in ketosis. Fat adaptation takes a much longer time. It’s not an on/off switch. If you are eating sub-20 grams of carbs per day and remain conscious, yes you are burning fat and producing ketones. But your cells and organs are not using them efficiently yet. It takes time for the synthesis of ketones and fat burn to get in sync with your daily energy requirements. By fasting you force your metabolism to burn fat/ketones exclusively (with the exception of those few cells that can not utilize fat/ketones and require glucose). This works fine after you’re fat adapted and utilizing ketones and fatty acids efficiently. Before that, however, you may be running on empty.
So, you’re starting from zero again.
Try keto-ade at least once per day during your next fast. The recipe is here on the forum. It’s just adding himalayan sea salt and magnesium citrate to water. It costs pennies per serving. It has helped tons of us with the dehydration symptoms of fasting. I still use it after a year of keto and dozens of 3 day fasts. It works.
Just wanting to say hi and welcome Smitty Girl. and nice info amwassil. So I may not be fat adapted either, as much as I cheat! 