16:8 Fasting - Glucose 74 - Ketone 5.6 - Is it safe?


Hi everyone,

I have been doing intermittent fasting 16:8 with a low carb high fat diet for a while and I workout 6 days a week while fasting and 4 of those days are High Intensity Training - Kickboxing.

Last week I took my glucose and ketone measurements for couple of days before I break my fast and few hours after eating my first meal and these are the numbers I had:

Glucose 79 - Ketones 4.5
Glucose 74 - Ketones 5.6
Glucose 83 - Ketones 3.8

I would love to hear everyone’s thoughts on:

  • Is it safe and ok for ketones to be as high as 5.6?
  • Should I be concerned?
  • Does this mean my body is still not fully adjusted to burn fat or is it the opposite?

Would love to hear your thoughts and your experience with this.

Thank you in advance!

(Bob M) #2

Blood ketones? mmol/l?

If you’re getting those values for ketones, I’d say you’re adjusted to burning fat. My theory would be that you might not be able to use the ketones what well, so your body is making more than strictly necessary. In other words, fast forward a year, and your ketones should be lower.

(Michael - When reality fails to meet expectations, the problem is not reality.) #3

If you’re not diabetic, and you’re not supplementing them, don’t worry about ketones. Your metabolism/liver will produce what you need when you need it. The amounts you measure in your blood are just whatever is currently in transit when you make the measurement. Unfortunately, there is no continuous ketone monitor that can display the hourly or even minute to minute variations in ketones. If we had such a device we would see very clearly how much the stuff varies and how rapidly. Your numbers look fine. Welcome to the forum.

(Bacon by any other name would taste just as great.) #4

Those ketone levels are right in the range for fasting ketosis. Diabetic ketoacidosis doesn’t even start until ketones of 10 or above, and symptoms are not observable until ketones reach 20. With such low glucose readings, you are in no danger of diabetic ketoacidosis, even if you are a Type I diabetic. It you are taking your daily insulin properly, or if you are not Type I diabetic, then diabetic ketoacidosis is not something you need to be worrying about.


Thank you Bob,
Yes its blood ketones and its mmol/l.


Great, thank you Michael,
No, I am not diabetic and was not supplementing. From the sounds of it, its safe to continue as is. Thank you again for the article and your reply.


Thank you Paul,
No I am not diabetic and am not taking any insulin. Good to know then that’s not something to worry about. Thx once again for your reply.

(Bob M) #8

I’d say, simplistically, glucose + ketones = energy. So, you’ll see that if glucose goes down, ketones up, and vice versa.

This is in general, though. I’m sure there are variations, particularly around exercise.

I have also found a decrease in my own ketones over time (7 years). What I think is happening is that my body (ie, muscles) can use ketones much better. Thus, the amount of ketones that “float around” are less.

But I’m sure exercise changes this too. I’m exercising only 3 days per week. You may (ok, do) need more energy, thus higher ketones.

Also, my “low” blood sugar is higher than your blood sugar. I think this is also an adaptation for me over time. I’m not sure whether that’s normal or I’m an outlier.

But those numbers aren’t bad. I’ll be interested to see what happens over time.

(Michael - When reality fails to meet expectations, the problem is not reality.) #9

I’ll throw this out for consideration simply because it seems to get lost in discussions about ketones. I don’t know exactly how it fits this particular discussion, but I’m sure it does somehow. :roll_eyes: The brain is the biggest ketone hog in the body. This simply because other forms of fat can not pass the blood/brain barrier. So I think it’s a valid assumption that most ketones (talking primarily β-hydroxybutyrate here) get utilized by the brain, secondarily in other cells that lack mitochondria. So at any given moment of measurement, most β-hydroxybutyrate is either on it’s way to the brain or already there. So here’s a testable hypothesis: when engaged in some ‘brain-intensive’ activity - brain exercise rather than muscle exercise - one could expect blood ketone levels to be lower as more β-hydroxybutyrate would be occupied in the brain rather than in transit.

It just occurred to me that you might even be able to measure changes in brain activity with an IR heat detector gun. I’m awaiting arrival of an order I placed online with Walmart. Once that arrives I’m going to place an order for an IR heat gun and see what I can do with it.

EDIT: Goof on my part. Mitochondria are required to metabolize ketones, so cells that lack mitochondria, like red blood cells, can’t use ketones.

(Bob M) #10

I have an IR thermometer, which I use all the time. Great for determining oil temp, temp of your pan you want to use to sear steak, how hot your water is, how cold your concrete basement is relative to the 2 inches of foam you added, etc.

I really can’t grasp the relationship between blood sugar and ketones. For instance, the LMHRs tend to have high BS (and ketones), and I thought that was because they also tend to exercise a lot. Makes sense to me that if you’re exercising a ton, high BS would help, say to replace glycogen.

And Shawn Baker at one time had a super high HbA1c, which also made sense to me. That guy is a manimal. He’s not human, really.

But he did something - I’m not sure what - and he’s showing BS in the 50s after exercise. How is that possible?

As for something like the brain, I assume that and muscles get good at using ketones. But all I do all day long is think, and my (blood and breath) ketones are super low. The last blood ketone I took was a week or so ago, in the morning. 0.1 mmol/l.

If my brain uses ketones, why such a low value?

Part of this is because my morning BS is higher, and my ketones are lower. At night, it’s the opposite: BS lower, ketones higher. This is why it’s an “equation” to me: BS + ketones = energy.

But then you look at someone like Zach Bitter. He sometimes runs a marathon every day (on average). He does supplement carbs, but I wonder if he HAS to supplement carbs? How much protein/fat can one person convert over time to blood sugar to help with glycogen replacement (and for whatever else needs carbs)? I assume he’s over that limit.

As for ketones changing, I don’t think they really change that much. Similar to BS, if you’re keto, your BS is pretty stable. I think ketones are similar. I’ve tested multiple times per day, and they seem to not change that radically.

(Bacon by any other name would taste just as great.) #11

This is an intriguing idea, but to me, Michael, the way you’re expressing it here feels somewhat off the mark. I don’t know if the brain soaks up β-hydroxybutyrate quite the way you seem to be describing it. I’ll happily agree, however, that the brain thrives on ketone bodies, noting, however, that all three of them cross the blood-brain barrier and can feed the brain, not just β-hydroxybutyrate.

Dr. Georgia Ede says that certain portions of astrocytes, portions that are too small to contain mitochondria, cannot do without glucose; on the other hand, Prof. Benjamin Bikman has challenged the notion that the brain needs any glucose at all. What is known is that the brain thrives on ketone bodies, especially when it becomes insulin resistant, since apparently brain cells require insulin in order to be able to absorb glucose. I think I remember from some reading a while back that acetone has some role to play in brain function apart from its role as fuel, but what, precisely, that role may be, I have forgotten.

It has also been demonstrated recently that all three ketone bodies, not just β-hydroxybutyrate, have epigenetic effects that regulate major systems in the body, so I believe that our understanding of the benefits of a well-formulated ketogenic diet can only grow over time. It feels to me as though there is far more to discover.

(Bacon by any other name would taste just as great.) #12

What do our levels of serum β-hydroxybutyrate and serum glucose actually tell us? Do we really know?

One possible answer might be that our measurement of circulating β-hydroxybutyrate shows only the momentary gap between production and consumption, and not the actual levels of either. I have no idea if this is correct, but it seems plausible, at any rate. So a possible answer to your question is that your low level of β-hydroxybutyrate could be because your brain is using a lot of it, no?

Does he supplement carbs? I know that after converting to keto he ran a couple of races with gels just to be on the safe side, but I thought he had said he didn’t really need them. Also, this sounds like a cop-out, but Dr. Phinney suggested that we not take Mr. Bitter’s remarks entirely as Gospel, given that he might be disseminating disinformation in order to conceal a competitive advantage. I don’t know about that, but that’s what the good doctor suggested.

What we do know is that the Inkinens rowed to Hawai’i on a completely keto diet and shaved a couple of days off the previous record while doing so. And I forget the name of the guy (though I seem to recall he is a Master Sergeant in the U.S. Army) who was keto and won the Western States 100, and who then ran a marathon the following day just for fun (didn’t win, but had one of the low finish times). Not my idea of fun, but there we are.

(Jane) #13

Those fasting numbers look fine to me.

The lowest glucose/highest ketones I ever measured was in Jan 2019 on my third day of a 72-hr fast - glucose 52 and ketones 7.6 I felt great.

(Michael - When reality fails to meet expectations, the problem is not reality.) #14

I’m currently trying to find pertinent details about brain/ketone usage and whether that might or might not affect blood ketone readings. I’m quite comfortable with the idea that all 3 ketone bodies can be utilized by the brain for energy and whatever else it uses them for. My understanding, though, is that β-hydroxybutyrate is the most plentiful of the 3. Also, I thought that red blood cells require glucose, not β-hydroxybutyrate since they lack mitochondria.

(Michael - When reality fails to meet expectations, the problem is not reality.) #15

Throwing out another idea that occurs to me. Why do humans enter ketosis and remain consistently in ketosis so easily compared to other animals? Because our big brains require a lot of energy and if we don’t get it we die. Although our brains can function on glucose, they function better on ketones. Why is that? Probably because for most of our evolution (at least 4 million years) ketones were our primary brain food. Glucose from gluconeogenesis was the backup system. It’s only since the last few thousand years that we’ve had consistent carb foods that bypass gluconeogenesis and ketosis. That’s about 0.2% of our evolution. No wonder there’s a problem with this.


Interesting what you say about acetone. This is the one measured with breath tests, isn’t it?

I’ll try to find papers on it, because mine is always above 0.1 %. I wonder if it means something. Could it be related to depression?


Do you feel alright? The way we feel is often a good indication of how our WOE is working for us.

Do you feel as if you had more energy now then with your previous WOE?

Welcome to the forums!

(Butter Withaspoon) #18

Exercise can raise ketones for a number of hours afterwards. Were your levels measured after the kickboxing?

Pretty sure it was Ben Bikman who mentioned that the main substrate for gluconeogenesis is lactate. Excellent recycling move by the body! Wish I could remember exactly where I read/heard this.

I’ve listened to a heap of the Zach Bitter podcasts and he definitely uses carbs at certain phases of training and for races above a certain level of intensity. He goes into so much detail and on multiple occasions; he’s not hiding his nutrition methods. It’s good for the podcast to discuss it. Human Performance Outliers if anyone is interested. Zach spends a few months every year in the off season being very low carb, to maximise the fat oxidation. Carbs are reintroduced strategically depending on training phase and intensity.

(Bacon by any other name would taste just as great.) #19

You are absolutely right! I don’t know what I was thinking when I wrote that. So much for keto clarity, eh? I have edited the post to take that bit of stupidity out. Sheesh!

(Bacon by any other name would taste just as great.) #20

Yes. Someone discovered that breath analyzers designed to detect alcohol also detect acetone on the breath.

We customarily measure acetoacetate in urine, acetone in breath, and β-hydroxybutyrate in blood, but this is a matter of convenience and ease of testing. I have read studies where it was β-hydroxybutyrate in the urine and acetone in the blood that were measured.