Cyclic Ketogenic Diet and Blood Glucose, HbA1c, Fructosamine, and Insulin

Blood glucoseCyclic Ketogenic Diet and Blood Glucose, HbA1c, Fructosamine, and Insulin

Brief Summary:

Recently I completed a 10 week experiment doing a variation of a cyclic ketogenic diet called the Carb Nite Solution, which basically entails eating strict low carb (less than 30 gm per day) with one 6-8 hr window of massive carb loading per week.  At the end of this experiment, before going on a trip to Italy, I had a series of fasting labs drawn.

So far we’ve looked at my:

Now I want to go over the labs reflecting my glucose control.

Fasting Blood Sugar

Carb Night 10 Weeks 2

Carb Night 10 Weeks


Just doing a cursory examination of my AM fasting sugars, you can see that they were all relatively well controlled, rarely going over 90 except for the mornings after my Carb Nites.  On the low carb days, I wouldn’t have expected much variation since I was eating such low carbs and the effect of the protein and fat I was eating on blood sugar is minimal.


This lab essentially measures how well your blood sugar has been controlled in the past 90 days by detecting how many hemoglobin molecules are glycated (have a glucose attached to it).  If your blood sugars are high, then you will have more glycated hemoglobin molecules, hence a higher HbA1c.  I wrote a longer post on this here if you want to read more.

HbA1c = 5.7% (Normal 4.8 – 5.6)

  • 5.7 – 6.4% = Increased risk for diabetes
  • > 6.4% = Diabetes

Estimated Average Glucose = 117 mg/dL

My HbA1c came in at a stable 5.7%!  It hasn’t changed one iota since I started measuring it here and here.  I still have concerns with the calculated estimated average glucose of 117 mg/dL, especially since I did an experiment measuring my blood sugars at 17 separate intervals while being in ketosis full time, and my blood sugars never got past 92 mg/dL.

I concluded at the time that:

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

I guess the good thing to take away from this is that my HbA1c remained stable despite the addition of the massive influx of carbs on Carb Nites.


This test is similar to the HbA1c in that it calculates your average blood sugar, except that it reflects values in the prior 2-3 weeks rather than the 3 months that HbA1c calculates.  This is because this test measures how much glucose binds to proteins in your blood (primarily albumin) which has a turn over of around 2-3 weeks.

The reason I wanted to get this test is to obtain another marker for my average blood glucose that is independent of RBC lifespan, which would confirm my explanation of why my HbA1c is higher than expected.

Fructosamine = 229 umol/L (Normal 0 – 285)

According to the equations found here and here:

HbA1c = 0.017 x Fructosamine + 1.61


Estimated Avg Blood Glucose = { [ (0.017 x fructosamine) + 1.61 ] x 28.7} – 46.7

Therefore, plugging in my fructosamine of 229 umol/L, my HbA1c should be 5.5% and my estimated average blood glucose should be 111 mg/dL.

While these numbers are slightly better than what my HbA1c indicates, I’m not quite sure it confirms my hypothesis of an extended RBC lifespan causing a falsely elevated HbA1c.

Here are a few issues for me to consider as I ponder these results

  • I should have drawn a serum albumin at the same time as I obtained this test.  For the same reason that the HbA1c can be falsely elevated or falsely depressed depending on the RBC lifespan, the fructosamine test can be susceptible to the rate of turn over of Albumin.  If my albumin was high… that could indicate a reason as to why my fructosamine is higher than expected.
  • The last 3 weeks of my Carb Nite experiment was when I started adding an additional Carb Nite into the week and that may have caused me to have more elevated blood sugars during the last few weeks of the experiment.

Fasting Insulin

Fasting insulin is perhaps one of the most convenient and practical methods to detect insulin resistance.  Insulin resistance is of course the thing we want to prevent when we avoid the carb heavy standard american diet, since it is associated with such badness as diabetes, obesity, heart disease, high cholesterol, high blood pressure, etc.

Fasting Insulin = 2.8 uIU/mL  (Normal 2.6 – 24.9)

The first question I had is what is the optimal range I should strive for?  Not just the normal, which as you can see is pretty broad, but the ideal range for optimal health.  Here are a few of the best resources that I came across:

According to Stephen Guyenet from the Whole Health Source:

So what’s the ideal fasting insulin level? My current feeling is that we can consider anything between 2 and 6 uIU/mL within our evolutionary template.

These folks think that:

When fasting insulin is over 5 µIU/mL, this indicates a metabolic problem such as pre-diabetes, which sharply increases risk for degenerative diseases.

In a fantastic post by Dr. Mercola he states that:

A normal fasting blood insulin level is below 5, but ideally you’ll want it below 3. If your insulin level is higher than 3 to 5, the most effective way to optimize it is to reduce or eliminate all forms of dietary sugar, particularly fructose.

So after looking into this I feel confident that I’m not insulin resistant and am pretty happy with these results.  The other thing I learned is how off the normal range provided is.  This again illustrates the importance of seeking health optimization rather than un-sickness.


After working through this post I’m finally able to pinpoint why I was so bothered by the discordantly elevated HbA1c despite having normal fasting sugars: I was worried that I had an underlying metabolic dysregulation such as insulin resistance, which would then subject me to an increased risk of all the badness that comes with it.  Seeing the normal but less than stellar fructosamine results also fed into this concern.


The fact that my fasting blood sugars are so good AND my fasting insulin is in the optimal range indicates that I don’t have an underlying insulin resistance, which is comforting.

This would then support my conclusion of a longer RBC lifespan as the reason behind the elevated HbA1c.  I still don’t have a clear explanation as to why the fructosamine levels are discordant with my bloods sugars (perhaps the additional carb nites?  maybe the equation is inaccurate? maybe I have a lower turnover of albumin also?)

In the future, rather than checking my HbA1c, I’ll preferentially test my fasting insulin levels as a better marker for cardiovascular risk.

… now if I could just figure out why body recomposition while doing ketosis or cyclic ketosis isn’t coming as easily for me as it is for others…

20 Responses to Cyclic Ketogenic Diet and Blood Glucose, HbA1c, Fructosamine, and Insulin

  1. Nadia Peters says:

    Interesting! Since my HbA1c levels show a similar tendency, I’ ll definitely have my fasting insulin levels checked at next testing. Very informative, thanks!

  2. mike says:

    I checked my last two blood tests, I do not see an insulin measurement.

    I can say for sure, my fasted glucose has been rising. It also seems to have risen directly from doing Carb Nite.

    Home testing showed morning levels of 90-95 and now they are 104-110, since starting low carb. I wonder if lowered insulin results in higher fasting glucose?

  3. KD says:

    I’d really like to know what you are eating and what you’re PPG values are.

    • Mike says:

      KD, who are you asking?

      • KD says:

        PPG is post prandial glucose or post “meal”

      • KD says:

        I’m asking both of you… If both of your fastings (FPG) are rising, then you need to look at what you are eating. What are the macros?

        When I eat carbs/or too many, the next day the FPG usually goes up and the ketones go down.

        And yes you’re FPG is rising due to your Carb night

        Above 100 fasting is already pre-diabetes, so you are eating yourself into pre-diabetes/diabetes.

        Look at Caveman’s #’s after every “Carb Night” his next day FPG’s shoot up to the pre-diabetic ranges. IMO too many carbs were eaten night before.

        Mike, lowered insulin does not result in higher FPG

        Caveman, an a1c of 5.7 and above IS pre-diabetes

        The other thing is diabetes/pre-diabetes is disease of insulin resistance, exercise and resistance training in particular is key to reversing this/improving insulin sensitivity.

        • BJJ Caveman says:


          I understand that an A1c of 5.7 is technically considered pre-diabetes, but I still don’t buy it in my case. When I was doing NK, eating less than 50 gm of carbs per day, there is no way my average blood sugar was 117. I even did a test on myself, eating a typical diet, testing 17 different times, and the highest my blood glucose got was 92.

          That’s why it was so puzzling for me, it just didn’t add up. There is definitely something else going on.

          As an example patients with polycythemia (too many RBCs) can have a falsely elevated HbA1c and patients with hemolytic anemia’s can have a falsely low HbA1c.

          Same with fructosamine, if you have an albumin dysregulation (hypoalbuminemia as with liver dysfunction) you can also have a falsely low fructosamine.

          To truly test my insulin sensitivity, I probably should check my fasting insulin while eating a higher load of carbs for a month… or just do my own glucose tolerance test at home. Drink something with 75 gm of sugar and check my sugars regularly for the next 3 hours.

          Also I don’t think the jury is out regarding fasting blood sugars on Carb up days on people who are ketogenic. After going all week with less than 30 gm of carbs and minimal insulin secretion, and then getting hit with a monster bolus of carbs 1 day of the week, there is a thought that it takes a while for the beta cells in the pancreas to upregulate their activity in order to secrete adequate insulin.

          Kiefer mentioned this in his most recent podcast on the Livin La Vida Low Carb show, although he did admit that there is no research out there looking into this yet.

          So who knows… it does give me something else worth exploring! Any suggestions for drinks containing 75 gm of sugar? I also wonder if it matters if the source is fructose vs glucose…

    • BJJ Caveman says:

      What doe PPG mean?

  4. KD says:

    So I’ll give you my experience…

    Since I’ve last tested my a1c since being on my strict NK diet and testing blood ketones daily, my a1c on 12/24 was 5.6. Today my a1c was 4.9%

    My fasting BG’s range from 60- mid 70s

    My blood ketones have ranged from 0.8-5.7. For the most part I know how to eat to keep them consistently above 2.5 mmol. All blood ketone tests are done fasting

    • Mike says:

      Any guesses on why my blood sugar is running high doing a CKD?

      They were 94 or so and now seem to be 10-15 points higher on average, measured upon waking (which I know can be higher).

      I am eating about 65-75% fat, Net carbs 20 or less, protein 90-130 gms.

      Fat loss appears to be going good 1-2 pounds a week while in a caloric deficit.

      How are you getting higher ketone levels? I know blood sugar has been noted to rise during low carb diets (Chris Kresser article)

      • KD says:


        are you doing resistance training? If you are I don’t see why BG would rise on a LCKD. Also how long have you been on LKCD?

        Also, how much do you weigh? and do you know your bodyfat %?

        And you say “net carbs”…are you actually eating any carb rich foods? What are you eating for your net carb sources?

        For fat sources, with the exception of my morning tblsp of coconut oil, and 2 avocados a day, some nuts, the rest comes mostly from saturated fats.

        • mike says:

          One HIT weigh training session per week.
          One home, short dumbbell workout a week.
          Occasional walking.

          55 days on Carb Nite CKD.

          Vegetables, nuts, coconut oil, fish oil, meat, minor dairy etc.

    • BJJ Caveman says:

      Wow, looks like your blood sugars have really come down, and those changes were reflected in your A1C!

  5. Saf says:

    hi caveman – you could try estimating your RBC lifetime, to validate your hypothesis, using the method here:

    • BJJ Caveman says:

      This is a fantastic article… comprehensive. I might just need to do a summary post of this.

      I haven’t had my reticulocytes measured yet, so can’t make the calculation, but I definitely will be adding it on to my next panel.

  6. Mary says:

    Dump your carb nights and follow a true ketogenic diet and body composition will follow.

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