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Why Your “Normal” Blood Sugar Isn’t Normal (Part 2)


In the last article I explained the three primary markers we use to track blood sugar: fasting blood glucose (FBG), oral glucose tolerance test (OGTT) and hemoglobin A1c (A1c). We also looked at what the medical establishment considers as “normal” for these markers. The table below summarizes those values.

Fasting blood glucose (mg/dL)<99100-125>126
OGGT / post-meal (mg/dL after 2 hours)<140140-199>200
Hemoglobin A1c (%)<66-6.4>6.4

In this article, we’re going to look at just how “normal” those normal levels are – according to the scientific literature. We’ll also consider which of these three markers is most important in preventing diabesity, diabetes, and cardiovascular disease. But before we do that, I’d like to make an important point: context is everything.

As I mentioned in Part 1 of this article series, there are potential problems with how well these tests are utilized to diagnose diabetes. This is an area that needs further study, but continuous glucose monitoring for the general population may be a better marker.

In my work with patients, I never use any single marker alone to determine whether someone has a blood sugar issue. I run a full blood panel that includes fasting glucose, fasting insulin, A1c, fructosamine, uric acid and triglycerides (along with other lipids), and I also have them do post-meal testing at home over a period of 3 days with a range of foods.

If they have a few post-meal spikes and all other markers or normal, I’m not concerned. If their fasting BG, A1c and fructosamine are all elevated, and they’re having spikes, then I’m concerned and I will investigate further.

On a similar note, I’ve written that A1c is not a reliable marker for individuals because of context: there are many non-blood sugar-related conditions that can make A1c appear high or low. So if someone is normal on all of the other blood sugar markers, but has high A1c, I’m usually not concerned.

With all of that said, let’s take a look at some of the research.

Fasting Blood Sugar

According to continuous glucose monitoring studies of healthy people, a normal fasting blood sugar is 89 mg/dL or less. Many normal people have fasting blood sugar in the mid-to-high 70s.

While most doctors will tell you that anything under 100 mg/dL is normal, it may not be. In this study, people with FBG levels above 95 had more than 3x the risk of developing future diabetes than people with FBG levels below 90. This study showed progressively increasing risk of heart disease in men with FBG levels above 85 mg/dL, as compared to those with FBG levels of 81 mg/dL or lower.

What’s even more important to understand about FBG is that it’s the least sensitive marker for predicting future diabetes and heart disease. Several studies show that a “normal” FBG level in the mid-90s predicts diabetes diagnosed a decade later.

Far more important than a single fasting blood glucose reading is the number of hours a day our blood sugar spends elevated over the level known to cause complications, which is roughly 140 mg/dl (7.7 mmol/L). I’ll discuss this in more detail in the OGGT section.

One caveat here is that very low-carb diets will produce elevated fasting blood glucose levels. Why? Because low-carb diets induce insulin resistance. Restricting carbohydrates produces a natural drop in insulin levels, which in turn activates hormone sensitive lipase. Fat tissue is then broken down, and non-esterified fatty acids (a.k.a. “free fatty acids” or NEFA) are released into the bloodstream. These NEFA are taken up by the muscles, which use them as fuel. And since the muscle’s needs for fuel has been met, it decreases sensitivity to insulin. You can read more about this at Hyperlipid.

So, if you eat a low-carb diet and have borderline high FBG (i.e. 90-105), it may not be cause for concern. Your post-meal blood sugars and A1c levels are more important.

Hemoglobin A1c

In spite of what the American Diabetes Association (ADA) tells us, a truly normal A1c is between 4.6% and 5.3%.

But while A1c is a good way to measure blood sugar in large population studies, it’s not as accurate for individuals. An A1c of 5.1% maps to an average blood sugar of about 100 mg/dL. But some people’s A1c results are always a little higher than their FBG and OGTT numbers would predict, and other people’s are always a little lower.

This is probably due to the fact that several factors can influence red blood cells.

Remember, A1c is a measure of how much hemoglobin in red blood cells is bonded (glycated) to glucose. Anything that affects red blood cells and hemoglobin – such as anemia, dehydration and genetic disorders – will skew A1c results.

A number of studies show that A1c levels below the diabetic range are associated with cardiovascular disease. This study showed that A1c levels lower than 5% had the lowest rates of cardiovascular disease (CVD) and that a 1% increase (to 6%) significantly increased CVD risk. Another study showed an even tighter correlation between A1c and CVD, indicating a linear increase in CVD as A1c rose above 4.6% – a level that corresponds to a fasting blood glucose of just 86 mg/dL. Finally, this study showed that the risk of heart disease in people without diabetes doubles for every percentage point increase above 4.6%.

Studies also consistently show that A1c levels considered “normal” by the ADA fail to predict future diabetes. This study found that using the ADA criteria of an A1c of 6% as normal missed 70% of individuals with diabetes, 71-84% with dysglycemia, and 82-94% with pre-diabetes. How’s that for accuracy?

What we’ve learned so far, then, is that the fasting blood glucose and A1c levels recommended by the ADA are not reliable cut-offs for predicting or preventing future diabetes and heart disease. This is problematic, to say the least, because the A1c and FBG are the only glucose tests the vast majority of people get from their doctors.

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OGTT / Post-Meal Blood Sugars

If you recall, the oral glucose tolerance test (OGTT) measures how our blood sugar responds to drinking a challenge solution of 75 grams of glucose. I don’t recommend this test, because A) it’s not realistic (no one ever drinks 75 grams of pure glucose), and B) it can produce horrible side effects for people with poor glucose control.

However, there’s another more realistic and convenient way to achieve a similar measurement, and that is simply using a glucometer to test your blood sugar one and two hours after you eat a meal. This is called post-prandial (post-meal) blood sugar testing. As we go through this section, the numbers I use apply to both OGTT and post-meal testing.

As the table at the beginning of this article indicates, the ADA considers OGTT of between 140 – 199 two hours after the challenge to be pre-diabetic, and levels above 200 to be diabetic.

But once again, continuous glucose monitoring studies suggest that the ADA levels are far too high. Most people’s blood sugar drops below 120 mg/dL two hours after a meal, and many healthy people drop below 100 mg/dL or return to baseline.

A continuous glucose monitoring study showed that sensor glucose concentrations were between 71 – 120 mg/dL for 91% of the day. Sensor values were less than or equal to 60 or 140 mg/dL for only 0.2% and 0.4% of the day, respectively.

On the other hand, some studies suggest that even healthy people with no known blood sugar problems can experience post-meal spikes above 140 mg/dL at one hour. As I said in the beginning of the article, context is everything and all of the markers for blood sugar must be interpreted together.

If post-meal blood sugars do rise above 140 mg/dL and stay there for a significant period of time, the consequences are severe. Prolonged exposure to blood sugars above 140 mg/dL causes irreversible beta cell loss (the beta cells produce insulin) and nerve damage. Diabetic retinopathy is an extremely common (and serious) diabetic complication. Cancer rates increase as post-meal blood sugars rise above 160 mg/dL. This study showed stroke risk increased by 25% for every 18 mg/dL rise in post-meal blood sugars. Finally, 1-hour OGTT readings above 155 mg/dL correlate strongly with increased CVD risk.

What does it all mean?

Let’s take a look again at what the ADA thinks is “normal” blood sugar:

Fasting blood glucose (mg/dL)<99100-125>126
OGGT / post-meal (mg/dL after 2 hours)<140140-199>200
Hemoglobin A1c (%)<66-6.4>6.4

But as we’ve seen in this article, these levels depend highly on context and whether all markers are elevated, or just a few of them.

If you’re interested in health and longevity – instead of just slowing the onset of serious disease by a few years – you might consider shooting for these targets. But remember to interpret the numbers together, and also remember that blood sugar is highly variable. If you wake up one morning and have a fasting blood sugar of 95, but your A1c and post-meal numbers are still normal, that’s usually no cause for concern. Likewise, if you see a one-hour post-meal spike of 145 mg/dL, but all of your other numbers are normal, that is also usually no cause for concern.

Fasting blood glucose (mg/dL)<86*
OGGT / post-meal (mg/dL after 2 hours)<120
Hemoglobin A1c (%)<5.3

*If you’re following a low-carb diet, fasting blood sugars in the 90s and even low 100s may not be a problem, provided your A1c and post-meal blood sugars are within the normal range.

Another key takeaway from this article is that fasting blood glucose and A1 are not often reliable for predicting diabetes or CVD risk. Post-meal blood sugars are a more accurate marker for this purpose.

And the good news is that this can be done cheaply, safely and conveniently at home, without a doctor’s order and without subjecting yourself to the brutality of an OGTT.

I’ll describe exactly how to do this in the next article.

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Join the conversation

  1. Simona,

    High cortisol can cause insulin resistance, and vice versa. Low cortisol can cause hypos during the night. Insulin upregulates 17-20 lyase in women, which converts estrogen to testosterone and causes androgen dominance.

    Unfortunately this stuff is very complex and it’s impossible for me to say more without knowing the particulars of your case. There’s no one-size fits all approach. Over-feeding may work in some people whose metabolic function is still relatively intact (though under-functioning), but I don’t believe it’s a good strategy across the board.

    • Chris — How long after I’ve eaten anything do I have to wait before I do a pre-meal test with my glucose meter?

  2. Thanks Lynn,
    I have his free ebook. I have been low carb (50 g veg carbs) low Pufa (o6 only from meat, olive oil and eggs, o3 about 2 grams for a while, stopped it) and low sugar, low fruit, no wheat, no pulses for more than two years (aug 2008). Minimal supps. I was only increasing potatoes and sweet potatoes (see also Paul Jaminet’s blog) for the last month. I should be doing better, but still struggling with gum disease/infections, even worse than a year ago, acne, hairloss, weight loss stall. Wide ranging hormonal issues, I think, cortisol affecting inflammation, underlying androgen (5 alpha reductase) problems due to possibly inherited insulin signalling problems. Just guessing here, trying to make sense of it. Couldn’t get a clear PCOS diagnosis in the last 10 years I’m suffering of these symptoms. More recently low T3 shows the metabolism slowed down, the cause of which is not clear.

    • my sugar was up last nite when i got off wotk to 177,, then todat it was 120 fasting,then after supper it was 199, then a hr later it wen to 106 it seemsthe more i move it goes down and when im stressed i havto take anxiety pills .every nite to sleep ,,plus i got a heraniated disc my bs has bee good till i hurt my back ,,,any ideas

  3. Simona

    If you want to try Matt Stone’s protocol, I would suggest you pick up his free RRARF eBook. His program is not just about increasing carbs; it is also very low fructose and very low in PUFA’s. There are other parts of it too.

    Also, feel free to email him. He is very responsive to emails.

    I have tried everything to get my insulin down and eight years of low carbing has done nada. So, I am trying the Ray Peat program. It is high carb too; but is extremely stringent re: PUFA, meat etc. The only thing Stone and Peat have in common with the SAD is that they both include carbs. However, thereoin they are world’s apart. Just raising carbs ala SAD won’t help at all. The biggest misconception re: Stone is that he advocates junk food and junk carbs. He does not. 🙂

  4. Thanks Lynn, these conditions have killed my brain! Am looking forward to the next article, I’ll be picking up a monitor shortly.

  5. Hi Chris,
    I have two questions. You have been very kind and answered many already. I hope it’s not too much to ask.
    Regarding that effect of raised post prandial glucose after reintroducing carbs, I remember there was a day when I had two very small boiled potatoes in a salad with protein and fat for lunch and I felt very sleepy after a while. The idea was to help revv up my metabolism (a la Matt Stone) I got a bit scared but now (after reading Stephan and you) I understand that it takes time for the body to adapt. However, my body shows signs of previous hyperinsulinemia, like skin tags, small acanthosis nigricans, I was wondering how can I know if it’s still a problem after two years of low-carbing and losing weight. Is insulin resistance not the cause? Would high-cortisol (chronic stress) cause high insulin too and then high androgens (which is also a problem)?
    My mother has diabetes type 2 for the last 25 years or so. She has had severe hypos and some of them happen at night. What could be the reason for a hypo at 2-3 am when there isn’t much basal insulin left (taken at 8 a) Is the glucagon/epinephrine release necessary to get glycogen out of liver not working?
    Four questions, not two.

    Thank you.

  6. Hi Jo

    To convert US units to mmol/L, simply divide by 18. So, a US unit of 90 divided by 18 = 5.0 in the UK, Ireland and Australia units. To convert an Aussie unit of 5.0; multiply by 18 = 90.

    My blood glucose monitor is in the MMMOL/L units, but since all literature I read is in US units, I convert instantly and focus on the US number.

  7. Hi Chris, firstly thanks for your posts, I’ve read them all and it is helping me in my plans to manage some diagnosed and undiagnosed problems. I want to monitor my blood glucose levels as they have been creeping up in FB tests. I had an OGTT, came in under range, but not a lot. I live in Australia, is there any chance you can convert the lab values you recommend into the common ranges we have here? Our fasting levels (IMVS labs) are “normal” at 4 to 6 mmol/L, and two hours post OGTT <7.8 mmol/L


  8. I’ve seen patterns like that in my practice and it’s pretty typical of cortisol dysregulation. That may be why your fasting blood sugar is elevated as well. The normal pattern would be a blood sugar peak 45 minutes after eating, returning to baseline by 2 hours. Something is raising your blood sugar in a fasted state, and cortisol (and/or glucagon) are the likely culprits.

  9. Hi Chris,

    What a timely post. I have been low carbing at about 50 carbs average per day for the past 21 months. I don’t normally check my BS but, was curious when I did do a FBS to find my morning level at 115. Then, I read about the phenomenon of LCers having high morning levels and felt a little more reassured. I have been checking my post-meal levels for the past few days and I am pretty confused. One hour after eating my level will be around 101 and two hours later it will be at 113. Even after three hours it is still going up, say to 119. I will have had nothing to eat or drink during this time. Is, perhaps, my meter not working correctly? Shouldn’t my levels be decreasing after that first hour postprandial?

  10. Angela,

    I think high intensity strength training is the best type of exercise for restoring and maintaining insulin sensitivity and glucose utilization. I’ll write an article about this soon.

    • Hey Chris I have a very important question it’s regarding my 2 year old daughter. Ive noticed she acts weird sometimes she would ask me for water constantly or ice and would sweat uncontrollably or would just lay down for long periods. My mom, brother and maternal grandmother all have diabetes. One day I decided to check her blood sugar and it was 135 after that I kept doing it regularly and one day I noticed it went to 187 and her fasting reading would be 95 105 or 114 and so on but it would never be under 90. Is this something I should be really concerned about? I contacted her doctor and they will run tests on her but they don’t seem like its a huge concern. What would be your advice?

    • chris – please do! i’m excited to hear about techniques we can use to keep our blood sugar in the healthy range.

  11. Hi Chris
    Thank you for your blog. It comes at just the right time. For the second time this year, my A1c was 6.0, so my doctor now wants me to do a 3 hour glucose test but I’ve been very weary of doing this (especially since my fasting glucose is 78). Your post-meal monitoring makes more sense to me. I know that I should be concerned that I might be pre-diabetic (even though I’m skinny). I’m looking forward to learning how to do this. Also, what kind of exercise do you feel is best to keep blood sugar levels down?

  12. Thanks, Chris, that’s encouraging. I’ll check out your site. I have learned a lot from your blog.

  13. Usually it can be addressed. It depends on what’s causing the problem in the first place. For example, if it’s “lifestyle”-related (i.e. diet, stress, sleep, etc.) and it’s early enough in the process it should be possible to completely restore healthy metabolic function. If it’s autoimmune, or has progressed long enough to where beta cells have been destroyed, then insulin signaling may be permanently damaged. In that case it would be a case of improving insulin sensitivity and glucose utilization to the fullest possible extent, and making dietary and lifestyle changes to prevent further damage. Feel free to check out my professional site and book a free 15-minute consultation if you’re interested in pursuing this further.

    • Chris, how can you tell if your beta cells are being destroyed? I usually follow a strict diet but at times I “just have to have something, (i.e. cookies, bread, muffin, etc.) and then my BG shoots way up, sometimes almost 300. Is it really bad to have these spikes?

      • Hi Jean – hopefully Chris has the time to jump in here too – but I’ll add my 2c worth as well:

        Beta Cell function can be measured somewhat using the C-Peptide and insulin-level tests. If you have decreased levels of c-peptide (a protein) it’s indicative of beta-cell damage.

        If you have decreased c-peptide but hyperinsulinemia (high-insulin levels) – that’s usually an indicator of insulin-resistance, and it may be possible to still maintain your pancreatic function without insulin, if you reduce your carbohydrate levels enough to compensate. If you have low-insulin levels as well as decreased beta-cell function, then it’s very possible your beta-cells are damaged to the point you may need additional insulin to manage your condition, or go VERY-low-carbohydrate in order to manage your glucose.

        My own experience – I managed to damage my beta-cell function without realizing it. Now I MUST eat very-low-carbohydrate to manage by glucose levels what little insulin production I have left. I don’t need basal or bolus insulin at this point in my life, but I *DO* keep my carbohydrate intake UNDER 20g maximum per meal. 15g maximum for any snack. Depending on my activity levels for the day I may have as little as 30g of carbohydrate, or as much as 90g. Typically it’s 45-60g in a day. That’s as a 220lb man eating 3,000 calories a day, BTW. That’s how low I need to go to keep my glucose “in-check”.

        As for BG shooting up to nearly 300… YES, that’s really bad. It is physically damaging you – no if’s, and’s or but’s about it. Anything above 140mg/dl is causing damage – period. This is agreed upon by all experts in the field (with the exception of the ADA who seems to want you to be on medication and damaging yourself…) and is in position statements from both the IDF (International Diabetes Federation) and the AACE (American Association of Clinical Endocrinologists).

        Unfortunately many of us MD’s as well as nutritionists, dieticians, diabetic-educators and others go by the recommendations of the American Diabetes Association (or in my case the Canadian Diabetes Association) simply because that’s the information we’re presented. Much of our continuing education is sponsored by the pharmaceutical industry – so it’s really no surprise that misinformation is rampant in those occupations.

        Chris’ blog post here shows exactly why blood-sugar levels are important, and gives it straight, and all research I’ve ever seen shows it to be “spot-on” for targets.

        Please, for your health’s sake, keep those spikes under 140mg/dl.

        • Thank you Glen for that info. I’m curious – do you have to use medication/insulin? Do you eat a lot of protein? My goodness, 15 g. carbs per meal is hardly anything. I don’t know if I could keep it that low. I eat a lot of veggies plus I probably eat 3-4 fruits a day. Thanks again.

          • Hi Jean – at diagnosis I was a very unhealthy 320lbs, with a fasting level of 267mg/dl and HbA1c of 12.1% … Not good.

            Initially my own doctor prescribed insulin, metformin and sulfonylureas … but after research I decided to ONLY go on the metformin and see about controlling everything else through a very-low-carb/ketogenic diet.

            As of now I have an HbA1c of 5.6% and virtually-all of my post-prandials are under 130mg/dl, unless I’m sick or very stressed. I’ve dropped 100lbs in the past year getting this under control.

            Yes, I eat considerable amounts of protein, usually a minimum of 35% of my calories – but I’m also exceptionally active. I work out a minimum of 5 days a week, (weight-training, HIIT, and cycling in the summer) usually for a minimum of 75 – 90 minutes. In the summer I’ll do 5 to 6 hour bike rides on days-off or weekends. With that level of activity I find I need the protein in order to maintain my lean-mass.

            I eat TONS of veggies – between 6 and 8 cups a day most days. I eat very little fruit. I’ll have at most two very small servings (like 1/2 of an apple or 1/4cup of berries) in a day. All the nutrients available in fruit you can get in vegetables with fewer calories and way less sugar. =)

            • Glen, first of all, congratulations!!! for what you’ve done for yourself! Hope I will be able to take this seriously and get my diabetes under “real control”. I must admit I find it hard to give up my fruit! I usually have a banana every morning (but at least I am trying to buy smaller ones these days). I know bananas are one of the worst for diabetes. One hour after my breakfast this morning (3 oz. turkey burger, banana and 1/3 c. whole milk, 1/3 c. 1% milk with my coffee) my reading was 167. Guess that’s not good huh? Again, thanks for your feedback.

              • I used to love bananas too – and I still eat them – sort of…

                I buy GREEN bananas (less ripe = less sugar) and peel them and freeze them … then use 1/3 to 1/2 a banana in a post-workout smoothie if I’ve done exercise enough to deplete glycogen pretty severely.

                Otherwise, I just don’t eat them.

                I think you’ll find if you cut out the banana, maybe substitute an egg (from free-range chickens, if possible) and cut the milk (especially the 1%) you’ll have much better post-breakfast glucose levels.

                My typical breakfast is 2-3 eggs, 2 strips of nitrate-free naturally-cured bacon (free-range pork), and I skip the coffee too. There are many diabetics that don’t respond well to caffeine – I’m one of them. This provides me between 400 and 500 very low-carb calories (depending on the number of eggs I eat). My post-prandials at breakfast are virtually identical to my fasting numbers, maybe 10 points higher at most.

                If I’m exercising in the morning I’ll also add 1/2 slice of organic, sprouted-grain bread (no flour!) with 1/2 tbsp organic/natural peanut-butter and 1 tsp no-sugar-added organic jam – usually raspberry. This adds another 100 calories – 12g of carbohydrate, 4g of protein and 4g of fat.

                • Hi Glen,

                  Can you give me information about Nitrate free naturally cured Bacon? What kind and where you buy them. I dont find anything without Nitrates or Nitrites, forget about the free range pork


      • I agree, once again, with Glenn. C-peptide is a cheap and readily available way to indirectly test beta-cell function. It is definitely bad to have spikes up to 300, and it’s indicative of deteriorating insulin sensitivity and glucose tolerance. Not a direction you want to be moving in. It’s possible that by addressing the underlying causes of your condition, you may be able to recover some carbohydrate tolerance. However, if there has been beta-cell destruction, it’s likely you’ll need to maintain a low-carb diet to prevent those spikes. Your cravings can be addressed through proper nutritional treatment (identifying and addressing nutrient deficiencies). Best to find a practitioner skilled in treating metabolic issues with a natural approach. Good luck.

        • thank you Chris …..you say readily available …. is this a test one can do themselves …. a “kit” you can get at the pharmacy? Or do you need to see a doctor? I’m sorry, but I’m new at all this stuff (was diagnosed with diabetes quite a few years ago, but just recently took it really seriously)…… really appreciate your site. Oh, another ? ….. what do you think about the “peak” training? 30 sec. high intensity and then 90 sec. rest, etc. ?

          • C-Peptide is only available from a lab. It requires special equipment to analyze – so no home test is available.

            As for training – what you’re calling “peak” training is likely what is referred to as HIIT – “High-Intensity Interval Training” and it’s by far the best exercise you can do as a diabetic – it’s also great for almost anybody – but it’s shown in several studies now to burn more fat and decrease insulin-resistance compared to moderate cardio.

            Weight-training, sprints with rest in-between, jumping rope on/off, etc. are all good examples and very beneficial.


            also, don’t over-train: http://chriskresser.com/why-you-may-need-to-exercise-less

          • You’d need to see a doctor to get cystatin-C. What I meant by readily available is that it’s not an exotic test your doctor hasn’t heard of. Any Labcorp or Quest lab can do it.

    • what do you mean by low carb? can this be followed just by anyone? is carbohydrates the culprit of causing diabetes? would you pls tell me the cause of diabetes? because if the real cause is identified i think the problem of what kind of food to eat will be settled.

  14. Chris, thanks again for your advice. So do you think I should eat a low-carb diet, monitor BG to keep it under some level (140?), occasionally check HbA1c, and continue to exercise regularly? Should this prevent further trouble? Can the metabolic problem be improved, or just worked around carefully?

  15. Mark: if you’ve always had that response, and if you feel sleepy after carby meals, I wouldn’t recommend the carb re-feeding. That’s indicative of a metabolic issue, and it’s probably not wise to potentially push your blood sugars above 200 in light of this.

  16. Thanks for your thoughts, Chris. I may give your carb-up test a try. I think I may have always had this response to carbs, at least the reactive hypoglycemia part. I get a little sleepy after an unusually large meal, which in the past has always meant a meal with plenty of carbs. I used to think everyone reacted that way. Maybe my mom’s side of the family (where the CVD is occurring) all have this too, staying mild enough to not trigger investigation for diabetes, but causing damage. My wife (a doctor) and a friend (a nurse) both are very skeptical I could be T2 diabetic, perhaps because I am not overweight and seem healthy. But BG of 237 is not healthy! Do you think I should get a HbA1c test to assess the current damage level?

  17. Mark: that kind of pattern is consistent with reactive hypoglycemia, which is often the earliest stage of the progression towards diabetes. I’m glad to hear you’re now eating low-carb, as BG of 237 after a potato is definitely cause for concern.

    If you’ve been LC for some time, it’s possible your body has adapted to burning fat and that’s why your glucose tolerance is impaired. The only way to find out would be to eat a higher amount of carbs over a 3-day period. If your blood sugars start to come down, it suggests you are adapted to fat burning but don’t have metabolic damage. If your BG stays high, it suggests you’ve got some metabolic damage that needs to be addressed.

  18. Chris,
    This is very interesting. I recently started eating fairly low carb, trying to follow the guidelines of the Perfect Health Diet (thanks for reviewing that, great book!) Then I got a FBG among other screening tests, because suddenly three elderly members of my family have been stricken by cardiovascular disease. The FBG was 110 mg/dL, causing me to investigate and freak out. Using a cheap glucometer I found evidence of the “dawn phenomenon” (83 mg/dL fasting usually, but 95-100 in the morning, have not repeated the 110 lab value). More shocking, I ate 8 oz of potato and it spiked my BG up to 237, down to 169 at 2 hrs, then mildly hyperglycemic (70 mg/dL) for a couple of hours. Response to a normal low-carb dinner was pretty benign. I did not mention the potato test to my doctor, who is unconcerned. I don’t know what to think. Looking forward to your next post!