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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Chris, I have written to you before. My triglycerides still are 34.
My fasting blood sugars are around 74 to 80. Two hour blood sugars run 140 to 179 but they are down the next morning in the 70’s with a rare 80. My doctor said because I have thalessemia minor I have triple chance of having diabetes. She is adamant that I have diabetes and is prescribing Metaformin. I also walk every day alternating 4-5 miles a day. I am 5′ 8″ tall and weigh 144 lbs. What would you do?
Linda, your numbers do not seem close to diabetes, although the post meal numbers may be higher than recommended. Could be the type of foods you are eating. Everyone else is getting the Hemoglobin a1C test, or average glucose over 3 months essentially. I never heard of anyone having very normal fasting numbers and being Diabetic. If the a1C comes out more than 6.0, then maybe you have some concern to improve. Your post sounds fishy — its off base somehow, which also seems to be what your are wondering.
can you provide a recommendation for the 1hr post-meal spike? thanks!
When I was first diagnosed with type 2 diabetes in January 2015, I weighed 203 lbs. I weigh 172 pounds today 4/21/15. I changed my diet and I exercise. My blood readings are between 120 and 106. Is this OK?
Hey! Have you taken a blood sugar reading in the morning before eating? If you take readings throughout the day, before and after eating, for several days and never get under 100- you have an issue. Just losing some weight is good but won’t necessarily “reset” you to not being sensitive to carbs.
hh, mix high carbohydrate foods with higher fiber plant foods to slow the digestion of sugars. fast digesting sugars cause high spikes after meals.
I have had severe peripheral neuropathy for several years , am overweight and am now developing multiple “trigger fingers”. All my lab tests indicate that my blood glucose is borderline at worst and I have no contributing back problems. Is it possible to have diabetes and not show on all the standard lab tests? I have a strong family history of diabetes and multiple symptoms, but my labs always say otherwise. What’s up?
First, I am no expert on diabetes, but have some experience with it.
Secondly, could you provide more information as to your lab tests. When were they done, what were the actual numbers? Do you also check your levels at home? How frequently?
I’m assuming your B-12 has been checked and is normal.
Hello Chris,
My doctor says im pre diabetic.
My last readings were;
A1c 4.6%
mg/dl was 146 thats what has me concerned. What type of regular diet should I be on? I am african american mid fifties.
I have not been too active but kniw i gotta get off my tail and into some kind of exercise
146 at what time? If you had a meal rich in crabs one hour after the meal this wouldn’t be a prediabetic number. Buy yourself a glucose meter and do regular measurments over a period of several weeks. Generally, one hour after the meal, you should be below 140, two hours below 120. If you get consistently higher numbers then you should first try to do regular exercises and watch your diet. Takes about 30 days for such an effort to have an effect on blood sugar.
Marty,
What if they ate shrimp, not crabs? Would that hep?
Bruce, I LOL’d!
My last blood work was:
Fasting glucose 104
Insulin 4.8
A1C 5.6
Do these numbers mean I’m prediabetic?
Thanks!
Just one borderline number does not make you a prediabetic. You need to take several measurements done within a period of time to confirm it. Although, there is a study by the NIH stating that even lab measurements scan be 5% off.
I had my CDC done 11-20-2013 and then one 07-09-2014 and another 12-31-2014:
11-20-2013:
Glucose: 82
HBG: 12.2
07-09-2014:
Glucose: 97
12-31-2014:
HGB: 12.5
A1C: 6.1
LDL: 142
HDL: 45
Tri: 106
Chol: 208
The dr. said I am pre diabetic?!?!!
Desiree, the A1C number is why he said that. Its supposed to be <6.0 for normal. Though the guru's doing all the studies and writing the books say 6.0 is still too high for normal. I got 5.8 and read that is too borderline for good health. Review the article above and this info is there, with 5.3 as the better target. A1C is an estimated 3 month average. If you really want to know your risk then getting your own measurements is best–you can see Kimberly below where I explained how to go about it to her. I have about 5 weeks of data now and feel much better seeing the variations over the day and various meal and workout situations.
You mentioned low carb diet a few times. What percentage of total calorie intake would you term a low carb diet?
A real low carb diet is 25 grams of carns a day or fewer. A moderate low carb diet could be anything between that and 100 grams a day.
Hello,
What constitutes “Fasting”? How many hours approximately?
I had at Random Glucose test at Kaiser yesterday. My level was 94.
I had a fresh juice (kale, celery, pear) 2 hours before the test and a full lunch 6 hours before.
Thanks!
Kimberly, Kaiser is expecting 12 hours with water only for fasting. The fresh juice will spike sugar readings but after 2 hours it should go back to the basal between meal normal. I recently got a meter and upload the data to look for trends. Kaiser prescribed the VERIO IQ meter which only has Windows App software. if you have a mac like me you can create an upload collector account for your meter on diasend.com Weirdly, I found my readings can be normal fasting numbers in the afternoon typically, while after 10 hours fasting I am pre-diabetic every day. I am so glad I got the meter since all my years of annual Kaiser 12 hour fasting levels have no meaning after all. If you get this curious and can spare the extra $20-30, the ACCU-check fastclix is very handy for the blood droplets. So much quicker than single prick lancets.
I was on tradjenta for 1/2 yrs and metformim – all seemed fine.
I recent had a peptide serum test that was low . I was also taken off tradjenta 2 weeks ago. On Metformin 1000 2x a day.
This was all from primary doctor.
Now my blood sugar is going up. a1c up and peptide serum low.
I scheduled an appointment with an endocrinologist – I think its time!!!!
You need checked for GAD, HLA, ICA, IAA, IA2, IgA antibodies. If they won’t run the tests run out the door. Your screaming LADA.
My daughter’s fasting blood sugar has been running 95-125, 75- 100 2 hours after meals. Just curious why the fasting number is higher than the 2 hour after meal number? She has been watching carbs more. Thank you for your time!!! Jennica
My fasting blood sugar is 99 and two hours post meal is 92. Why would fasting be higher?
Helen, that is too close to trust the single measurement. You should repeat this a few times to uncover a trend. My own self testing would make me think the meter is not exact every time and your meal may not have had carbs or sugars. But I have also seen this a few times myself when the meal was quality fat and protein like chicken or fish. Somehow I guess that digestion work is lowering the glucose present in the blood. Maybe that explains your numbers?
Please help my
fasting blood sugar:94
1 H After food: 100
2 H – 123
2h:30m – 94
That looks quite normal. The meal may have included complex carbohydrates which would take a bit longer to raise the blood glucose-but the spike is modest and soon returning to fasting levels.
Totally agree with Andrew, however the numbers are not ideal and if its possible to change diet and exercise to reduce these lower it would be a great thing.
Hi, my fasting glucose reading this morning was 91. I ate breakfast and tested one hour later, it was 96, then I tested again another hour later, (total of two hours after eating) and it was 100. I am using the FreeStyle Freedom Lite meter. They seem like strange figures to me. My A1C in the past has been 5.7 to 5.9, so a little high. What do you think? I am on Synthroid now because the thyroid was eliminated with radio active iodine. I have to stay on the hypo end of normal with the Synthroid, or I will go into atrial fibrillation. Maybe everything works together? Thank you.
Most of my life I have been told my sugar is a little high. But until the last year, I had never taken it serious . Then I picked up a meter at a friends urging. I was shocked to find my sugar sitting at 250 an hour after eating a half of a chicken sandwich. This has my attention. For the last few months, I have checking my sugar at different times through out the day, depending on how I am feeling. My fasting sugar usually ranges between 106 – 120. After eating I have seen spikes as high as 350 . For years I have been told I was pre-diabetic. With numbers like this, should I ask the Dr. to prescribe metformin.
Post meal readings like that strongly indicate diabetes even if your fasting glucose is normal & probably requires medication.
Post meal spikes like that also indicate you have a poor diet that may be high in carbs, especially processed and simple carbs, like sugar. You need to watch that. I have switched to a mostly vegetarian diet with fish (not fried, but baked with no additional oils). I don’t put any additional oils on anything, and I don’t buy anything packaged that has more than 1 to 3 grams of carbs total (packaged meaning prepared meals, etc.). I eat a LOT of greens, beans, and other veggies. I brought mine from a normal 350 to 77 between meal to 90 post meal in just a couple of weeks. My fasting level is still 115, but that’s because your liver starts producing glucose to compensate for the fasting. A little protein snack before bed helps that a little.
Oh, and exercise is extremely vital! I can’t stress that enough! When you exercise, your body is less insulin resistant, especially if you work the muscles. Muscles burn a LOT of glucose in a short amount of time. Doing things like fast walking from your car to the store, or climbing a few flights of stairs every day will make a HUGE impact on your glucose levels.
For health and weight management I maintain a pretty low carb diet. I lean toward paleo and alkaline food regimens, watching the volume of high calorie healthy fats. I am also religious with green smoothies and greens&vege juicing in moderate amounts 5 days a week. My fasting glucose is generally higher this way but my triglycerides stay down 75 to 85. I am trying to validate if this is more healthy, while riding a nominal 104 glucose? I just started home testing and have a high of 115 after paleo dinner with red wine. I have been drinking a shot glass amount of boiled turmeric powder daily for a few months. In addition I started gymnemma with meals. My HDL has been steady at 60. I would still like to get pre-meal glucose below 90 to feel safe. Family history is bad heart disease so I am motivated to keep experimenting and following the success of others.
The greens are good. Also throw black beans in the mix (and other beans, but not broad beans). I stay under 40 on the glycemic index, and it has made a world of difference. I also cut out most animal protein, except fish. I also do some form of exercise every day because your muscles will burn a lot of glucose in a very short period of time. For example, I tested at 120 this morning waking up. I ate mostly greens all day, ran down 22 flights of stairs and walked back up (about 11 minutes) and i dropped to 77 Mg/dL before dinner. After dinner I was 93. That is pretty normal. I will also add that I am on a couple of meds, including metformin, but those only brought me down to about 120 for a couple of weeks. Exercise, greens, and beans are the key! I do no bread, potatoes, and other high GI carbs at all anymore.
Derik, thanks for sharing. I eat pretty similar to you, not so much on beans – my wife just started adding black bean and lentils into dinners. The early morning exercise seems like a good habit if I can swing it- I like it after work when I am loose and awake after sitting most of the day.
Yeah, I usually stay up too late to get up early to exercise. I am working on my sleep now, and have lowered my caffiene intake significantly, because around 8 hours of sleep is vital for a diabetic. That is when your body normalizes many chemicals in your body, including hormones that cause or limit weight gain. Obesity is linked to lack of adequate sleep. Exercise in the morning lifts your metabolism, and breakfast spikes it even more so that you don’t crash as hard in the afternoon and do things to feel good, like drink alcohol, or eat at the wrong time of day.
I really think that attacking the diabetes type 2 with a low carb diet and exercise for the first few months really does the trick. Today we had a retirement lunch for one of our employees. I ate a very large piece of stuffed pizza (crust on the bottom and top, HUGE carbs), and a very rich piece of cake. 1 hour later I was at 132, then 2 hours later, after walking up 12 flights of stairs, I was at 91. Right now, I am at 77. I am still on glipizide still, but I will bet it wouldn’t be very far from my BG without glipizide. Exercise after meals seems to be the magic bullet as well. I am really getting pretty excited about this.
So when I test my blood sugar in the morning time ,most times it reads like 79-85,I checked it the other day after a meal and it was an hour after and it read 144 , now I’m worried as to if I am diabetic….,can someone answer me this question?pleease……..thanks
Fasting readings absolutely normal-post meal a bit high (but not diabetic level) unless it was very high carbohydrate. Why not try a few more post meal readings after varying the meal ?
If they’re consistently high you may be on the way to developing impaired glucose tolerance (a possibly pre-diabetic condition) – but on the evidence of the readings you’ve provided you’re definitely NOT diabetic now.
What you are describing is a perfectly normal scenario for blood sugar levels. You’re fasting blood glucose levels are fine, and it is completely normal to have a slight spike, as is yours, after a meal.
Exactly. The damage to your body comes from long periods of time at constant high levels (weeks or more). I have read people spike as high as around 140, especially if they had bread, potatoes and other high GI carbs with their meal. Perfectly normal.
I have to correct or clarify my above statement. I say “normal” but only if it goes back down to a baseline of 70 through 90 in a couple of hours.
Luara,
As the article said, any one reading that is a bit outside the norm when all other readings are normal is nothing to worry about. If you have fasted levels of less than 90 and an A1C of less than 5.7 then your 144 post meal reading is not a big deal as long as it lowers within 2 hours or so.
Can someone clarify or elaborate on this?
“One caveat here is that very low-carb diets will produce elevated fasting blood glucose levels. Why? Because low-carb diets induce insulin resistance. ”
Everything I’ve read about insulin resistance or avoiding diabetes urges one to incorporate a low carb diet.
Thanks!
It happened to me. I went for a routine physical, my fasting glucose was 96, when it never before had been over 85. I got freaked out, bought a meter, started testing myself. Got very high readings after eating. I started researching. Here’s one article. https://www.marksdailyapple.com/does-eating-low-carb-cause-insulin-resistance/#axzz3OvjQe99y
For some people it has that effect. Never again will I go low carb.
It’s not inherently low carbing, it’s the incidences of minimal carbohydrate intake after extended intervals of time, as opposed eating small amounts spread evenly thoughtout the day
I’ve been monitoring my blood sugar for several years. Lately my fasting blood sugar has averaged 122 over a 14 day period of time. Seems like the more I limit carbs the worst it is, but like others are told to limit carbs to reduce FBG
I have read that it is because, since you aren’t loading your body with glucose through the day, your liver produces it from fat and protein breakdown at night, during the fast. It’s normal to have a higher fasting reading. It should go down through the day once you start eating though. Mine does.
Your fasting & postprandial glucose results look excellent, can’t understand why your A1C is 5.9% -would have expected much lower.
This seems to be a consistent theme on these postings -interesting to know why.
A1C is the accumulation of glucose on the red blood cells over time (a few months) which is why it is a good indicator of your average blood glucose and can prove prediabetes even when your BG looks normal when you test it (it may not be normal when you aren’t testing it). Frequent high spikes that you don’t catch can cause a higher A1C.
My FBG is between 70-80, my post-meal glucose (about 1 hour after) is 95-118 (the high # after generous portion of beef liver dish and 3 flax seed tortillas), but my A1c came out at 5.9%. I did start regularly exercising and strongly restricting my calories about a month ago, so I might have had less stellar #’s previously, but I just measured them over the last few days with home test kits to see how close to the brink I was. I have been 50-60 pounds overweight for a long time now, plus am of South Asian descent, so I have reason for concern, but hopefully with getting back to exercising regularly and controlling my diet, I can undo some of the damage. Regarding my #’s, should I just wait another 3 months to take another A1c and see what it looks like, or is there major reason for concern and I should head to the doctor?
How do I get to the next article?
Here’s a link to the next article:
https://chriskresser.com/how-to-prevent-diabetes-and-heart-disease-for-16
My mom is 80 with Alzimer
her FBS is 200 . she take 1 metformin and 1 glybanglamid in morning and same intake in the evening,
have you any idea about it