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.
| Marker | Normal | Pre-diabetes | Diabetes |
| Fasting blood glucose (mg/dL) | <99 | 100-125 | >126 |
| OGGT / post-meal (mg/dL after 2 hours) | <140 | 140-199 | >200 |
| Hemoglobin A1c (%) | <6 | 6-6.4 | >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.
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.
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:
| Marker | Normal | Pre-diabetes | Diabetes |
| Fasting blood glucose (mg/dL) | <99 | 100-125 | >126 |
| OGGT / post-meal (mg/dL after 2 hours) | <140 | 140-199 | >200 |
| Hemoglobin A1c (%) | <6 | 6-6.4 | >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.
| Marker | Ideal |
| 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.
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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When I stay strict paleo, I see my post prandial and fasting numbers are in the ideal range for the most part. When I deviate by having say a piece of pizza and pineapple my post prandial shoots up to 150-170.. So how do I find the medium ground in terms of how many carbs I should target in a day?
I have posted as “Susie~Q” and “Susan”. I have a question. A lot of times my blood sugar will not spike until the second hour, it fools me on the first making me think all is well, then WHAM, it can be anywhere from 139 to 150, by 3 or 3 1/2 hours, I am pretty close to my starting level.
I am taking all kinds of lowering herbs, I guess they help some, but sometimes, when I do not take them, my blood sugar is lowering, like the herbs are working opposite of what they should do.
I’d rather estimate lower, unlike another had posted. I am inclined to agree that these numbers are closer to normal. We should be trying to meet the levels of healthy people, not the numbers of known diabetics using insulin. I, for one, totally appreciate the information published here.
…… just another quick question, why are old posts shown at the top? Would it not be better to sort them with the newest at the top so that people can see the latest news?
Steve
Hi Chris
For the most part we are told that having elevated BSL causes heart problems, kidney problems etc; etc. My friend who is 76 has never taken any type of medicine (insulin, metformin) due to lack of trust in the Pharma companies and has had this for over 45 years without any type of side effect. The few times he has taken his morning levels they were always between 240 and 320.
I was diagnosed with chronic pancreatitis at the beginnig of the year at age 62 with diabetes as a side effect. Metformin made me really ill so I was put on 26 units of insulin (Lantus) at night and 6 units of rapid (Humalog) before every meal. 2 months after taking the insulin, my average fasting levels were 169 (anything between 130 and 250). Like my friend, I distrust the Pharma companies. So I Googled it and came up with gymnema sylvestre as an alternative. After 1 month of this my levels had dropped and I needed to stop the Humalog because of hypoglycemia (down to 60ish fasting). After 3 months of taking this supplement I have been able to cut the Lantus down to 10 units.
Now my average fasting levels are 112 (for a 2 month period).
Firstly, how come my friend isn’t either dead or seriously ill with complications of high levels? Secondly what do you know about gymnema sylvestre?
All I can tell you is it works for me.
It also works for my friend as I told him about it and now his fasting levels are down to a pretty stable 130 – 140. Not brilliant but much improved on before (he still eats what he likes).
I wish everybody on this site good luck with their quest for normal levels.
Steve
Hello, I have just discovered your site and am very glad I did! I just finished reading this article and cannot seem to find the next one where you talk about to accurately take post prandial blood sugar readings, can you or someone else here direct me to it? Thanks!
Suz…
Hi!
Are the measurements in whole blood or plasma? I have heard that there is a difference between them.
Your numbers sound great to me. Why do you keep checking? I am always in the 90’s to 100, fasting, have ALWAYS been that way for me this us normal everyone is different, we can’t all be text book perfect.
I do spike at times, I come down after 2 1/2 hours, again, this is normal for me. I have been this way since I was 26, I am now 57 and in great health.
Hello! (I’m from Sweden so I apologize in advance for my spelling!)
I have a question that I don´t seem to find an answer to anywhere. My FBG is all over the place. I can test 10 times at home within 15 minutes and I get numbers from 76 to 109. If I take the middle value of all the readings I get 89 which is borderline high and indicate diabetes within a decade. My postprandial values are always good. I don´t ever spike and don´t get a number over 120 ever. I can go under 100 after 45 minutes sometimes. My HbA1c levels are also good and within a normal range according to the article. I can´t understand why my FBG differs. I am underweight and have been my whole life which is genetic. My BMI is 17,3 and I rarely eat more than 1300-1500 kcal a day. I counted my carbs and I guess I eat less than 130 a day. I don´t strive to be low carb I just eat little of everything. Can my BMI and diet be the reason why my FBG are borderline high? Should I do something about this?
Thankful for any answer!
Have you considered your meter at home may be inaccurate? I was convinced for 3 months I was diabetic until I started having my doctor test me and always got normal results.
The article is very informative. Thank you very much.
How does all this fit with porphyria, where a high carb diet is vital – HIGH carb: 300 minimum, 400-500 during attacks?
RE: Posting of blood sugar and A1c numbers. I find myself unable to comment with the information given. It would be useful to post more specifics like BMI, number of carbs per day (and an idea of their sources), and amount/type of exercise, etc. What changes have you made and what was the impact (if any) seen via your experimentation? What have you done to confirm the accuracy of your meter? Any experimentation done with avoidance of key allergens and the observed impact (grains, dairy, soy, corn, etc)? Are you attempting to optimize cell membrane function (paying attention to )3-6 ratios and environmental toxins?
Yes, I agree with the comment about not getting too stressed about it. There is no ‘failure’ only feedback and the information IS useful as long as you are not discouraged about it. It may spur you to find answers in areas you hadn’t thought to explore (e.g. gut biome configuration). Even if you never are able to lower the overall numbers, you will likely get info on individual foods YOU need to avoid that will spike you.
This article is very frustrating. No matter what I do, my blood sugar is always over 100, and my A1C is usually around 5.4. There is simply no way for me to achieve the numbers in this article.(I never in my life had blood sugar numbers this low even when I was like 12 year old) BTW I have no family history of diabetes, I am normal weight and exercise every day and eat a diabetic diet. It all makes no difference at all.
I agree, for me, those numbers are an impossible, I will never be in the 80’s when fasting, oh maybe sometimes I am 86, but my “Norma” is in the 90’s.
I take tons of herbs to keep it down, such as Berberine, which consistently rates better than Metformin, I have no family history of diabetes, am normal weight and exercise most days, and watch my diet. For me, a good A1C is 5.7. Folks can say what they want, but that is my best. My blood pressure is low, and when I had an ultra sound on my carotid arteries a couple years back, the results were “stellar” to quote my doctor.
So, bottom line, I am not like others, and the numbers I have are good for me. I will add that I have been in these numbers since I was 25, I am now 56. I say stop worrying about what other folks are, worry adds high cortisol, high cortisol equals higher blood sugar. Accept the readings, especially if you are in good health and have always had such numbers. You are not diabetic, neither am I. We just do not fit the bill of others, but hey, that is fine.
Here!s to individuallity, and good health.
I would like to know what is considered an “ideal” hba1c? A few months ago, mine was a 4.9 and now it’s a 5.1. My doctor said not to worry, but are we trying to get it as low as possible? My fasting glucose is 85. I eat about 150 grams of carbs a day. Not low carb but not exactly high carb either.
Or if anyone else knows the name of the part 3 article that would be great. Thank you
I think I found Part 3: https://chriskresser.com/how-to-prevent-diabetes-and-heart-disease-for-16
Chris, I would love to read Part 3 of this article – what is the title please so that I can find it. And thank you so much for your invaluable information!
Hi Chris,
My FBG is in 80ss and post meal after an hour is usually 120-130 and 2 hour is between 90-110 but my A1c is always 5.9. I have changed my diet to low carb diet, no sugary sweets or drinks but still my a1c is not moving down even a bit. Is it a concern?.?
Hi, I dont think Chris comments on posts much, so I hope you dont mind my thoughts, as I have a similar situation. One possible explanation is long-lived red blood cells , this would explain the higher A1Cs despite lower fasting and non-spiking post prandial numbers. A1C can be like BMI – a general (but not personally specific) screening. 2) You may have a latent reaction that you haven’t ‘caught’ yet (numbers are spiking later than anticipated). This was what was discovered about the ‘low-carb’ Dreamfield pasta – the spike was as high as regular carb pasta, but it was happening later. 3). I am experimenting with a little higher carb diet to see if it actually lowers blood sugar. You may have read that if you are following a low carb diet, you will fail an oral glucose tolerance test, but that eating 100-150 carbs per day for 3 day prior to the test will reverse the physiological insulin resistance (this is a term you can google search for more ideas). 4) I am getting ready to evaluate berberine (‘herbal metformin’) to see what happens and am trying to eat a few more starchy carbs a la Jaminet PHD, as my 23and SNPs suggest I am genetically disposed to higher blood glucose numbers.
Which begs the question, why would you want to go on a low carb diet if it’s going to make you insulin resistant….
When i was pregnant i developed gestational diabetes and it never went away. Up until last year my fasting bs levels would be between 115-130 but i was able to keep my numbers under control for the rest of the day i.e. Under 120 after 2 hrs. I have to tell you i am overweight. I weighed 228 pounds. This past year i have been under extreme amounts of stress being a restauranteur so im sure my cortisol levels are totally out of control and in one year i have gained more weight bringing me up to 245 lbs with fasting numbers at 160-180 and i can no longer control my numbers throughout the day. The low carb atkins diet in which ive done before and lost alot of weight rather easily, is not working at all and my reading 2hrs after a meal is still at 140. Im having a hard time understanding first, why i cannot loose weight on atkins, and second why my numbers are so out of whack even when im not taking in the carbs. Cholesterol at last check wasnt too bad at 184 but they did say triglycerides where a bit high and good cholesterol was low. I am not on any meds and never have been except through pregnancy. Please tell me your thoughts. I know i need to lose weight and im trying but all diets seem to be failing.
Just an FYI and N=1 follow up to the whole BS discussion. I hope it will be enlightening to the discussion:
I have taken my Bayer Contour to the lab when I had my blood drawn in the past and it was very close to their results (i.e. therefore I presume it is accurate). I have been testing/comparing the NovaMax Plus meter (for glucose) because the same meter will do blood ketones and the sticks are reasonable priced vs. what they used to cost and competitors. However, there has been big discrepancies between the 2 meters so this morning I called the company. Overnight fasted glucose. Bayer meter read 82 and NovaMax read 145 (same blood drop). Based on my diet and past testing history, the 82 should be (I hope) correct! They had me do a control solution test on the NovaMax strips which read 119 (so this iswithin their ‘acceptable’ limits which are printed on the meter vial and are about the range of 82-127 I believe). They had me re-test my blood x 2. The first reading was 140 and 2nd was 137. By their standards, this is acceptable. I like this company and they are sending me replacement test strips just in case it was something about this batch (this lot is not from their ‘bad’ strips recall). This is just an example of why it helps to do repeat N-1 testing. I am going to add a 3rd meter to the mix. I believe Dr. Bernstein says Freestyle and Freestyle lite currently the most accurate.
I am a newly diagnosed Type 2 and am trying to control my blood sugar with diet and exercise. So far, I’ve been very successful, but I have a question: Why, when I eat the exact same breakfast two days in a row, does my postprandial glucose fluctuate so much? Yesterday it was 115, today it was 130.
Sounds like margin of error in the meter. What you eat up to 24 hours before can also impact the amount of insulin that is ‘stored’ in your pancreas – so that could have a minor effect as well. Have always been grateful I can check BS out of interest (not medication dosing). Think the device manufacturers should be held to a much tighter standard than they are. See Jenny Ruhl’s Blood Sugar 101 book and great on-line info and there is an interesting section in Tim Ferriss 4-hour body where he tests blood sugar (varied by finger, etc). I wouldn’t purchase the book but maybe stop by the library and have a look at that section.
Results can also depend on what your fasting blood sugars are. My results vary depending on where my blood sugar are before I start my meals. You can eat the same exact meals and get different results depending on stress levels, time of day, before meal readings, if you are ill. There are so many things that can effect results.