Ketones and glucose during fasting


I’m 27 hours in to fasting. I measured my ketones and glucose and my glucose is 66.7 mg/dl and ketones 5.3 mmols. I feel ok but had a small amounts of diarrhoea. Do you think I should discontinue fast. I never been this high on ketones. If anyone has any suggestions please let me know. Thank you all in advance.

(Bob M) #2

How do you feel? If you feel bad, such as being shaky, then bail. If you feel fine, then it should be okay.

What happens is that as your blood sugar drops, your ketones go up. Your ketones are higher, but not that high. (I used to get into at least the upper 4s.)

Ketoacidosis is high blood sugar + high ketones:


Hi I decided to end the fast after 30 hours. I felt ok otherwise. I think it just shocked me to be honest as I never had such high ketones before. I wasn’t too worried about glucose as I been that low before. I can possibly get in to such deep ketosis as I’m consistently in ketosis even after meals as it’s I eat very low carbs and very clean keto that’s why fasting possibly spread it up. I will have a luck at the article and maybe next time continue but longer.

(Bob M) #4

What should happen is that your ketones will go up as your blood sugar goes down. 5.x is fairly high but not unreasonable. Also, if you’re new to this, your ketones in general should come down after a while.

But the main thing is that you don’t feel bad. You can feel hunger, but if you start feel physically bad, then that’s not good.

I’ve seen people who had blood glucose in the low 30s, at the end of a week of fasting, but I don’t remember if they took ketones.

(KM) #5

How did you measure? Ketones in urine will go up (as a percentage of the volume) if you’re dehydrated, and if you have diarrhea that will dehydrate you. (I don’t know if dehydration raises blood ketones but it stands to reason it would, less water = higher percentage of everything else.)


Hi I measure with blood monitor. I have ended the fast. Still diarrhoea though so it had nothing to do with ketones really. Thank you.


Hi thank you for your reply. I think I just panicked tbh. Maybe it would be better not to measure and just go by how my body feels. I think the culprit is magnesium. I started taking glycinate as it’s supposedly kinder to digestive system but it’s still causing me problems. It’s beginning to cost fortune to try and find right supplements/ electrolytes.

(KM) #8

It’s not that the ketones and diarrhea have anything to do with each other. It’s that if you are dehydrated your ketones will be elevated.


Ohhh thank you I didn’t think of that. That is very likely.

(Bacon is a many-splendoured thing) #10

And 5.3 is right in the middle of the range known as the “ketosis of fasting.” Time to re-post Dr. Phinney’s famous chart, I guess:

The yellow-orange “starvation ketosis” range is where the ketosis of fasting lies. Starvation and fasting are synonymous terms, in the literature.

Note that ketoacidosis is not considered to begin until serum β-hydroxybutyrate reaches 10 mmol/dL, and even then, symptoms don’t start until around 20.0.

(Bacon is a many-splendoured thing) #11

You might be eating a bit too much salt. That can cause diarrhoea.

On the other hand, it could be the result of an infection or something, and the timing was simply a coincidence. If you get diarrhoea the next time you try fasting, however, that would be a different story.

(Bob M) #12

I like most of that figure, but I think it doesn’t use those of us who have been in ketosis for a while (10+ years), as our ketones are low. And even Virta’s results had people with ketones <0.5. The “post-exercise ketosis” is also misleading, as I have low ketones post-exercise.

Even “starvation ketosis” is a misnomer, because my last day fast, I didn’t get much above 2.0 mmol/l.

Ok, maybe I don’t like it that much. :face_with_raised_eyebrow:


I only been doing keto two months so that may explain high levels.


Thank you so much for explaining this to me. I have only been doing keto for 2 months and my ketones are normally high is. This put my mind to rest.

(Bacon is a many-splendoured thing) #16

All good points, Bob. Thanks for adding them.

(Bob M) #17

I shouldn’t be so condescending, as it does describe people who are new to keto pretty well. And I’m sure it’s helpful if you need ketones to be high, say for mental illness.

I would like to see more studies or other info as to what happens when you’re keto for a while. Say you’re doing keto for bipolar, depression, anorexia, etc. What happens to your ketones over time, and (more importantly) does it matter?

There’s a family funding a study for bipolar, because their son had bipolar, and what corrected it was keto. But do the effects of keto last … forever?

(KM) #18

Ya. So many variables and so much uncertainty with self reporting. I have a hard time being 100% certain of any changes in myself. Sometimes the excitement and self confidence that comes from doing something, Anything, that feels productive and pro-active, fuels the sense that a certain protocol is doing wonders. Then the new wears off and the “improvement” disappears and I start questioning the value all over again. Was it a short lived real improvement or was it just an emotional boost??

(Jane) #19

I used to test during fast with my old KetoMojo and the highest ketones I ever recorded was 7.6 after 3 days of fasting. My glucose was also the lowest I’ve ever seen - 52.

I felt pretty good, actually. Broke the next day.

I was working out of our Ft Worth office and it is a 7-hr drive home at the end of my work week. Since I sometimes had trouble with diarrhea breaking a fast I also broke the day before I had to get on the road, just to be safe.

eta: I didn’t start fasting until I had been keto for 9 months, so wasn’t a noobie. I am also one of those weirdos who after 7 years of keto can turn a pee stick pink on normal keto and dark purple when fasting. For most, the pee sticks stop working after a while.


That is fantastic Janie. I admit I am bit obsessed with it. After 20 hours fasting my glucose and ketones are equal. I find it unbelievable and no hunger or feeling weak. I would like to believe that I entered authopagy though I need to research more on the subject. Thank you for your reply.