When Your "Normal" Blood Sugar Isn't Normal (Part 1) | Chris Kresser
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When Your “Normal” Blood Sugar Isn’t Normal (Part 1)

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In the next two articles we’re going to discuss the concept of “normal” blood sugar. I say concept and put normal in quotation marks because what passes for normal in mainstream medicine turns out to be anything but normal if optimal health and function are what you’re interested in.

Here’s the thing. We’ve confused normal with common. Just because something is common, doesn’t mean it’s normal. It’s now becoming common for kids to be overweight and diabetic because they eat nothing but refined flour, high-fructose corn syrup and industrial seed oils. Yet I don’t think anyone (even the ADA) would argue that being fat and metabolically deranged is even remotely close to normal for kids. Or adults, for that matter.

In the same way, the guidelines the so-called authorities like the ADA have set for normal blood sugar may be common, but they’re certainly not normal. Unless you think it’s normal for people to develop diabetic complications like neuropathy, retinopathy and cardiovascular disease as they age, and spend the last several years of their lives in hospitals or assisted living facilities. Common, but not normal.

In this article I’m going to introduce the three markers we use to measure blood sugar, and tell you what the conventional model thinks is normal for those markers. In the next article, I’m going to show you what the research says is normal for healthy people. And I’m also going to show you that so-called normal blood sugar, as dictated by the ADA, can double your risk of heart disease and lead to all kinds of complications down the road.

The 3 Ways Blood Sugar Is Measured

Fasting blood glucose

This is still the most common marker used in clinical settings, and is often the only one that gets tested. The fasting blood glucose (FBG) test measures the concentration of glucose in the blood after an 8-12 hour fast.

It only tells us how blood sugar behaves in a fasting state. It tells us very little about how your blood sugar responds to the food you eat.

Up until 1998, the ADA defined FBG levels above 140 mg/dL as diabetic. In 1998, in a temporary moment of near-sanity, they lowered it to 126 mg/dL. (Forgive me for being skeptical about their motivations; normally when these targets are lowered, it’s to sell more drugs – not make people healthier.) They also set the upward limit of normal blood sugar at 99 mg/dL. Anything above that – but below 126 mg/dL – is considered “pre-diabetic”, or “impaired glucose tolerance” (IGT).

Oral glucose tolerance test (OGTT)

The OGTT measures first and second stage insulin response to glucose. Here’s how it works. You fast and then you’re given 75 grams of glucose dissolved in water. Then they test your blood sugar one and two hours after. If your blood sugar is >140 mg/dL two hours later, you have pre-diabetes. If it’s >199 mg/dL two hours later, you’ve got full-blown diabetes.

Keep in mind these are completely arbitrary numbers. If your result is 139 mg/dL – just one point below the pre-diabetic cut-off – you’ll be considered “normal”. Of course this is perfectly absurd. Diabetes isn’t like catching a cold. You don’t just wake up one day and say, “I’m not feeling so well. I think I got a bad case of diabetes yesterday.” Like all disease, diabetes—and diabesity—is a process. It goes something like this:

malfunction > disease process > symptoms

Before your blood sugar was 139, it was 135. Before it was 135, it was 130. Etcetera. Would you agree that it’s wise to intervene as early as possible in that progression toward diabetic blood sugar levels, in order to prevent it from happening in the first place? Well, the ADA does not agree. They prefer to wait until you’re almost beyond the point of no return to suggest there’s any problem whatsoever.

[End rant]

The other problem with the OGTT is that it’s completely artificial. I don’t know anyone who drinks a pure solution of 75 grams of glucose. A 32-oz Big Gulp from 7-11 has 96 grams of sugar, but 55% of that is fructose, which produces a different effect on blood sugar. The OGTT can be a brutal test for someone with impaired glucose tolerance, producing intense blood sugar swings far greater than what one would experience from eating carbohydrates.

Hemoglobin A1c

Hemoglobin A1c, or A1c for short, has become more popular amongst practitioners in the past decade. It’s used to measure blood glucose in large population-based studies because it’s significantly cheaper than the OGTT test.

A1c measures how much glucose becomes permanently bonded (glycated) to hemoglobin in red blood cells. In layperson’s terms, this test is a rough measure of average blood sugar over the previous three months.

The higher your blood sugar has been over the past three months, the more likely it is that glucose (sugar) is permanently bonded to hemoglobin.

The problem with the A1c test is that any condition that changes hemoglobin levels will skew the results. Anemia is one such condition, and sub-clinical anemia is incredibly common. I’d say 30-40% of my patients have borderline low hemoglobin levels. If hemoglobin is low, then there’s less of it around to become bonded to glucose. This will cause an artificially low A1c level and won’t be an accurate representation of your average blood sugar over the past three months.

Likewise, dehydration can increase hemoglobin levels and create falsely high A1c results.

The “normal” range for A1c for most labs is between 4% and 6%. (A1c is expressed in percentage terms because it’s measuring the percentage of hemoglobin that is bonded to sugar.) Most often I see 5.7% as the cutoff used.

In the next article we’ll put these “normal” levels under the microscope and see how they hold up.

332 Comments

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  1. rmarie,

    From what I’ve read, even relatively quick spikes can be harmful, but the effect worsens the longer they are elevated.

    A much better strategy, in my opinion, would be to avoid the spikes in the first place by not eating the foods that cause them, and by working to address the underlying mechanisms. Just my 2 cents.

  2. Chris, I’ve been wondering about something re A1C tests and BG spikes for which you may have the answer:

    How long does the blood glucose have to be in the blood to bond to the hemoglobin. Is it immediate? For instance if a high BG spike of say 180 is brought back down quickly (without medication) does it have enough time to bond? (and influence the A1c test result)?

    I’m asking because I have learned a little trick. For example, if I eat something I suspect may raise my BG I test it after 1/2 hour and if it’s high, doing 60-80 jumping jacks will lower it 30-40 points within 10 minutes. Works every time and I have NEVER experienced hypoglycemia. My base line tends to stay around 115-120.

    It’s very convenient and quick without having to spend an hour running or bike riding.

    • I thought that with exercise too but if the food was high enough glycemically…try testing your bg again after a while from the exercise. I think you will see the dramatic lowering from exercise was temporary.

  3. I’ll explain how to cheaply and easily measure post-meal blood sugars in a future article, which is probably a more accurate indicator of CVD and diabetes risk than OGTT anyways.

  4. I am definitely pre-diabetic (have been for at least 10 years that I know of) and yes, my doc never said anything because it was usually well below 126. One of the reasons I’ve never taken an OGTT is that I weigh 89 lbs and I think drinking 75 oz glucose for such a small body is irresponsible. And they probably wouldn’t adjust it. I watch my carbs and things have not gotten worse over all that time. I’m in my late 60’s.

  5. Hi Perkdoug- I did test it after several exhaustive sprint workouts and I now know that they definitely elevate my BG for a while. I didn’t really ever get super high readings though, usually between 95-115. I really don’t know how this compares to a healthy BG response to exercise but it doesn’t strike me as too excessive.

    Thanks for the tip.

  6. Tyler the sprinter:

    Test your blood sugar immediately after a high stress workout and you might see an unfriendly blood sugar level.

    Just an idea that could explain the high A1c.

  7. This is exactly what I was talking about in the article. I can’t understand why a doctor would be “pleased” by an A1c of 5.5 when 5.6 is often considered to be pre-diabetic. That’s lunacy. Does some magic button get pushed between 5.5 and 5.6 that changes everything? I don’t think so.

    As I’ll explain in the next article, nerve damage, beta-cell destruction and other complications begin to occur as blood sugars rise over 140 mg/dL. Believe it or not, heart attack risk increases in a linear fashion as A1c rises above 4.6%. Granted, the increase in risk from 4.6% – 5.5% is very mild, but from 5.5% – 6.0% it goes up significantly.

    You may need to reduce your carb intake. There are several other potential causes of high blood sugar, such as high cortisol, so that might be worth investigating as well.

  8. Hi Chris,

    Thanks so much for this article. I am new to reading your blog, but am very interested in learning more about blood glucose testing. I recently had some blood work done and because of a flaky reading on a fasting glucose test, my doctor reordered the test and an HbA1C test. While she was very pleased with the results (fasting of 90 mg/dl and A1C 5.5%), I thought the A1C seemed high. I purchased a blood glucose meter and have been doing some testing over the past week. So far the highest reading I have seen was 2 hours after eating a breakfast of oatmeal with butter, coconut flakes, cashew butter and about 2 Tbsp of honey. It was 141 mg/dl. That seems fairly high to me (for a presumably healthy person). Thoughts? (and FYI, I ate the same breakfast this morning without the honey and only hit 110 mg/dl)

    My plan is to continue testing after meals that are higher in carbs and see what foods tend to cause the highest spikes.

    …Tim

    • Most type 2 diabetics (non-insulin dependent) have increased b.g. after eating something carby like oatmeal with honey. An alternative could be flaxmeal porridge with coconut oil and cream. Mix a couple of tablespoons of flaxmeal with the c.o. & cream and heat. Add whatever sweetner you choose.

      BTW, my b.g. would probably be around 180 with the same meal.

      Best wishes…..

  9. Jesse: lab ranges are mostly determined by taking a bell curve of the results of those who get tested. And that is a huge problem I will be addressing in a future article.

    Java: eating will affect blood sugar, that’s why to obtain a fasted blood sugar reading (to see how the blood sugar behaves in a fasted state) it is necessary to fast for 12 hours. Many other things, such as cortisol levels, will also affect blood sugar in the fasted state. Being adequately hydrated is a normal physiological state, so yes, you should be adequately hydrated to avoid skewing the results.

  10. Hey Chris, what research are these tests and numbers based on? It’d be interesting to see how they came up with such values. Or were they just made up from nothing?

  11. Amazing article..does a state of fasting , as in early morning blood tests alter scores. Should one ideally hydrate before these tests. But then what is ‘normal’ ? Tests done in a state of hydration or tests done without hydration ?

    • That’s absolutely incorrect. Fructose is a glucose just like any other. As a kind 1, I am an perfect lab rat for “will something impact your blood vessels sugar” and fructose is no exemption. Melon is a fruits, the is know for fructose, and it has one of the biggest decided upon Glycemic Indices on the table.

  12. A normal life cycle for a red blood cell is 120 days. So when I say “permanent”, I’m just referring to that period of time. It’s absolutely possible to change A1c levels with diet.

  13. Dear Chris

    I’m not well-informed on this important topic, so please excuse my question. You write that “The higher your blood sugar has been over the past three months, the more likely it is that glucose (sugar) is permanently bonded to hemoglobin.” – Is this absolutely permanent? – Or does the bonded hemoglobin eventually get broken down so that the person ‘gets another chance’ at regaining unglycated hemoglobin?

    Thank you very much for your interesting and informative blog.

    Margaret

  14. I can’t say I remember my hydration status at the time, I’m usually well hydrated but it’s definitely possible that I wasn’t. I’m going in for another one soon and I’ll make sure to hydrate well.

    The previous months were physically stressful as I was doing manual labor all day, training for track, and weight lifting, but not mentally stressful. I was also during intermittent fasting at this time (probably stupid idea considering the workload). Certainly could have elevated cortisol.

    I’ll let you know the results from the next test. I really appreciated the answer, thanks again.

    Tyler

  15. Only thing I can think of that wouldn’t elevate FBG and post-meal BG, but would elevate A1c is dehydration. In this scenario, your hemoglobin would still be in the lab range but outside of what we call the “functional range”, which is the range that reflects optimal health. Polycythemia and erthrocytosis could do the same thing, but in that case your hemoglobin would be outside of the lab range.

    Were you under any additional stress during the previous 3-month period leading up to the A1c test? Cortisol elevations from physical (overtraining) or mental/emotional stress could elevate A1c, but we’d expect to see it in FBG and post-meal sugars as well.

  16. Hi Chris- been reading your blog for a while, I’ve used the information from here to treat clients with really excellent results. Your research quality and the application of it is really top notch.

    Quick question – I’m 180 lbs, intercollegiate sprinter/jumper, following a strict evolutionary diet for ~10 months, diet was very good before that too, about 8-10% body fat, and overall in great health. However in my last blood test, my A1c was 5.7%. I tested BG values for 2 weeks afterwards and it only went over 126 twice, and was usually between 80-90 (while eating my normal lowish carb diet). The doctor was completely stumped as to why my A1c was so high, as am I. My other blood values were normal- TGs: 48, LDL: 91, HDL: 111.

    Any ideas off the top of your head as to why this would happen?

    Thanks a lot for the great info on the site by the way, you are an inspiration.

    Tyler

    • A1C does not directly correlate to bg.

      For example, fructose can raise A1C, but not bg – I’m guessing that’s the cause as your LDL is a bit on the high side (gorgeous TG and HDL though).

      • That’s completely untrue. Fructose is a sugar just like any other. As a type 1, I am an ideal lab rat for “will something affect your blood sugar” and fructose is no exception. Watermelon is a fruit, the home of fructose, and it has one of the highest agreed upon Glycemic Indexes on the table!

        • I’m not arguing with the watermelon issue.
          However I do know you can spike your BG and not have it affect your A1c since A1c is a 3 month measure.

          This may be splitting hairs but it’s true. A single spike or two won’t raise your A1c like a 3 months run of high spikes will.

          This may be a moot point and nothing for any argument over.