The Effects of Nutritional Ketosis on HbA1c Part 1

Blood glucoseOne of the reasons I decided to switch from the Slow Carb Diet that I followed since the beginning of 2011 to nutritional ketosis was because I had a blood test that showed my HbA1c level to be 5.7% which placed me at an “increased risk for diabetes.”

  • < 5.7% is normal
  • 5.7% to 6.4% means you have a higher risk of diabetes
  • > 6.4% means you HAVE diabetes

I was surprised by having such a high HbA1c, especially since the main idea behind the Slow Carb Diet was to maintain glycemic control to decrease the amount of insulin fluctuations with the exception of one cheat day.  Since I was strictly adherent to the diet, the only possible explanation that I could come up with was that my cheat days exposed me to so much glucose, that it actually raised my HbA1c, placing me at increased risk for diabetes.  I chose my diet so that I could lose weight AND be healthier… but if it placed me at increased risk for diabetes, then the whole thing was pointless.

So when I came across the idea of nutritional ketosis which espouses even stricter control of glucose and subsequently insulin release WITHOUT the benefit of cheat days, I was ready to jump on the bandwagon.

Before I go forward, I should explain what HbA1c actually is and to do that I have to go into some basic biology.

  • Everyday your body makes new red blood cells (RBCs) and breaks down old RBCS at an equal rate so you have a constant number of RBCs (assuming you are healthy).
  • The lifespan of a RBC is somewhere between 100 – 120 days.
  • The main function of the RBC is to bring oxygen to your body by using an oxygen carrying protein called hemoglobin
  • When your RBCs are exposed to glucose, some of this glucose sticks onto the hemoglobin protein forming a sugar-hemoglobin
  • The more glucose there is, the more hemoglobin proteins it sticks to, forming more sugar-hemoglobins
  • Also, the longer your RBC is alive, the more it is exposed to glucose, hence it will have more sugar-hemoglobins
  • The HbA1c test measures the average percentage of sugar-hemoglobins of ALL the RBCs in your body, giving you an idea of how much sugar they’ve been exposed to in the past 90ish days.
  • So if you are diabetic, and your blood sugar is high all the time, you will have more sugar-hemoglobins, and thus a higher HbA1c.
  • This is an important tool that doctors use to track diabetics because even though they can have a normal blood sugar measurement (which is a snapshot in time), if their HbA1c is high, it tells the doctor that their blood sugar has been poorly controlled on average in the past 3 months.
  • HbA1c is a function of your blood glucose level and how long your red blood cells live.  If this were put into an equation it would look something like this:  
    • HbA1c ~ (RBC lifespan) x (avg blood glucose concentration)

So now that I’ve gotten all of that out of the way and bored you death I can go into what my HbA1c was after 72 days of nutritional ketosis.

  • Before starting nutritional ketosis my HbA1c was 5.7% which equates to an average blood glucose of 117 mg/dL (according to this calculator)
  • My average fasting AM blood glucose during 72 days of nutritional ketosis was 83.8 mg/dL which equates to an expected HbA1c of 4.5% (according to this calculator).
  • My HbA1c after 72 days of nutritional ketosis was 5.7%!!!!

When I saw that I was like WTF!!!!!!!!  WHY DIDN’T IT GO DOWN!?!?!

Possible explanations that crossed my mind were:

  • Maybe there was a lab error
  • Maybe my glucose is actually bouncing around a lot higher than it is when I measure it in the morning
  • Maybe I’m still eating too much protein leading to increased gluconeogenesis
  • Maybe I’m eating more carbs than I think, since I know that food labels can be way off
  • Maybe there’s something else going on with me (like a glucagonoma) causing me to have a higher glucose throughout the day even though I was eating very low carb and having a normal fasting AM level

I couldn’t believe that I was still at “increased risk of diabetes” despite being in prolonged ketosis confirmed with blood ketone measurements!  It didn’t make any sense at all!  If I was exposed to enough glucose to average 117 mg/dL, that means that I was also exposed to a lot of insulin which would then prevent me from reaching ketosis!  These are two mutually exclusive things!  HOW CAN THIS BE?!?!?!?

So I did what any rational person would do.  I went to google and found out that there were a few people out there who ate low carb with the same issue which you can see here and here, which made me feel better since I wasn’t the only person in the world to experience this.

Blood JournalThen I came across this article which offered the best explanation and helped me put 2 and 2 together.  He basically said that HbA1c can be an unreliable test because “there is actually a wide variation in how long red blood cells survive in different people.”  I actually found evidence in the scientific literature to support this, where they observed that there is a wide variation in RBC lifespans in normal people that actually can have a clinically significant impact on their HbA1cs.  Then there’s this paper showing that RBCs die faster when they are exposed to more glucose, which can also be interpreted as RBCs live longer when they are exposed to less glucose.

In my case, this all started to make sense, particularly when taking into account the HbA1c equation above:

HbA1c ~ (RBC lifespan) x (avg blood glucose concentration)

Since my HbA1c was high and I know from my measurements that my blood glucose concentration was normal if not on the low end, that means the reason for my elevated HbA1c must be that my RBCs are living longer.

Whew… what a sigh of relief.  My low carb diet and subsequent low blood sugars actually help my RBCs to live longer.  RBCs that live longer are then exposed to blood glucose for a longer period of time causing me to have a higher HbA1c.  My ABNORMAL lab result actually reflects a HEALTHIER change in my body.

The curious thing is, there is virtually no data out there in the scientific literature examining the effects of a low carb or ketogenic diet on HbA1cs.

Inuitively it should look something like this:

  • Low Carb -> Lower Blood Glucose -> Lower HbA1c

But from all the data I’ve just presented, it looks like it’s actually more like:

  • Low Carb -> Lower Blood Glucose -> Longer RBC lifespan -> Higher HbA1c

This means that all the reference ranges for HbA1c that we are currently using don’t necessarily apply to people who eat low carb or have good glycemic control.

Talk about barely scratching the surface of understanding how our bodies work and operating without a manual…

In part 2, I start another n=1 experiment to prove this to my self with actual measurements.

20 Responses to The Effects of Nutritional Ketosis on HbA1c Part 1

  1. Hemming says:

    That’s a very interesting observation. But how reliable is the equation? I’m thinking that it’s actually pretty poor (like most of these estimation). Just saying that one should be catious about getting ‘false’ hopes of improved from a single marker.

    • BJJ Caveman says:

      The equation is incomplete, but reliable in that it reflects what happens if one side goes up and one side goes down. ie if red blood cell life span goes down (seen in settings like hemolytic anemia or sickle cell anemia), then that will cause hba1c to go down.

      And when I put that equation a more accurate form would be HbA1c ~ (Total # of RBCs) x (Avg Blood glucose concentration)

      and the total # of RBCs ~ (RBC life span) x (Rate of RBC production)

      These equations aren’t meant to be quantitative.. but to represent what happens when one factor increases/decreases and how it effects the others. I probably should have made that clearer.

      “one should be catious about getting ‘false’ hopes of improved from a single marker.”

      I’m glad you brought up this point since I AM cautious and had to prove it to myself… I think you’ll find part 2 interesting.

  2. Daytona says:

    How frustrating to not have your A1c fall in line. I just wanted to share that in the LCHF diabetic community, we mostly see a lower A1c eating this way. I would caution against saying low-carb => higher A1c, it is definitely something that varies from person to person.

    I don’t have an answer for your why A1c hasn’t lowered. Some thoughts are:

    1: Are you testing your post-meal blood glucose? The fasting BG is the last to “go bad”. It could be that random chinese meals, protein shakes, etc may be affecting your BG more than you expect based on fasting readings.

    2: I know that anemia will cause the A1c to be lower than expected based on average BG levels. Maybe you have the opposite issue (not uncommon for men).

    3: There is a margin of error in the A1c, especially with the home kits. Are you getting yours done at the same lab each time? Give it more time, test again in another 3 months and skip the kits.

    Don’t let this discourage you! You have done a great job and seem to feel better on your current diet so it is worth sticking to it.

    • BJJ Caveman says:

      I got the lab tests from Quest both times.

      I’ve thought a lot about the other things you suggested, and I think you’ll find part 2 interesting.

  3. […] – A marker I wrote about before (Part 1, Part 2) that reflects how much sugar you’ve been exposed to over the past 3 months.  A […]

  4. […] I also got my HBA1C checked and it measured 5.7%, which hasn’t changed at all. […]

  5. Nadia Peters says:

    How interesting. Just read this post : my HbA1c was 6.1 after LCHF with no more than max. 100g carbs, and only from vegetables and some fruit (no wheat, potatoes, rice…) . I wrote a post about it here:
    Might my RBC’s be living longer? 🙂
    Found no other explanation until I hit your post!

    • BJJ Caveman says:

      I just commented on your site… but I figured it’d be good for me to copy and paste my response here so that others can read:

      Great numbers! It’s interesting to see how similar our numbers are!

      Also interesting to see the reference range you have for your A1C levels which is 4.0 – 6.0. My reference range is 4.8 – 5.6%.

      In a couple months I plan on also getting the fructosamine test, a measure of how much glucose is stuck on to certain proteins in your blood, which I think will confirm my thoughts on why my A1C is slightly high. It may be a test you want to consider also!

  6. […] will have more glycated hemoglobin molecules, hence a higher HbA1c.  I wrote a longer post on this here if you want to read […]

  7. Rick says:


    Just found your site and it seems we share a physiology. I’ve been ketogenic for over 2 yrs (80% fat, 5% Carbs) and my HbA1C is the same as yours. When I researched why I found the same papers and used them to convince my doc nothing was wrong.

    Similarly, My LDLs wigged out and increased like yours increasing from 150 to 230 while my TSH went from 2 to 5. I want to read your cholesterol posts closer but I think increasing carbs might be the right path for me as well even though I really like my current diet and would prefer not too.

    Thanks for the info

  8. Donnie Whetstone says:

    I’ve been KETO for years. My carbs rarely go over 25 grams per day. When I’m in contest prep, I can go 0 carbs for weeks on end while still training and doing cardio. Though my blood sugar stays within the mid 60s to mid 70s, I was surprised to discover my A1C at 5.8. I will do more diligence but what you’ve written is very plausible.

  9. […] meine roten Blutkörperchen länger im Blut sind und sich dadurch der Blutzuckerwert erhöht. Der Artikel sagt es […]

  10. Patrick says:

    72 days is a relatively short time. It’s best to have it done after 120 days or more. If your A1C had been around 7.0 you would probably notice a more dramatic drop, but you were only about 5.7–well within the .5 error rate.

    Ketosis also causes fasting blood sugars to rise a little. If your peak BS was lower but your fasting was higher, they could cancel each other out.

  11. Charles Grashow says:

    Maybe you need to rethink your use of a ketogenic diet.

  12. Stephanie L. Hughes-Cox says:

    I’m at a loss. I had my A1C tested last year an it was 5.4 then again in January it was 5.6. I started a ketogenic diet may 1,2017. I got a call from my doctor today that my A1C is 5.7. She asked me if I was really eating a very low carb diet and I said yes but she wants me to go to a nutritionist. 😐 I have lost 53lbs since May 1 and feel like staying under 20g carbs per day has kept me in ketosis. I have thyroid issues too (hypothyroid….then suddenly went hyperthyroid this past week so had to back off my meds). I’m at a loss as to what’s going on with me.

Leave a Reply

Disclosures: Please note that some of the links provided are affiliate links, and at no additional cost to you, I will earn a commission if you decide to make a purchase.  Please understand that I have experience with all of these products.  If they're books, I've read them cover to cover, and if they're products or supplements, I've used and/or continue to use them, and I am not shy about giving my honest opinion of them, positive or negative.  The small commissions I make help me out a tiny bit, and if you've found my site helpful then feel free to purchase these products through the links I've provided.  If not, that's fine too, no pressure, I'll still continue to write!  Please do not spend any money on these products unless you feel you need them or that they will help you achieve your goals.

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to and affiliated sites

Medical-Legal Disclaimer:

This site is not designed to and does not provide medical advice, professional diagnosis, opinion, treatment or services to you or to any other individual. Through this site and linkages to other sites, provides general information for educational purposes only. The information provided in this site, or through linkages to other sites, is not a substitute for medical or professional care, and you should not use the information in place of a visit, call consultation or the advice of your physician or other healthcare provider. BJJ Caveman and are not liable or responsible for any advice, course of treatment, diagnosis or any other information, services or product you obtain through this site.

Privacy Policy

See the privacy policy here.