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)||<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 diabetes and cardiovascular disease.
Fasting blood sugar
According to continuous glucose monitoring studies of healthy people, a normal fasting blood sugar is 83 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’s not. A study in Diabetes Care showed that the risk of heart disease increases in a linear fashion as FBG rises above 83 mg/dL. Another study in the same journal showed similar results.
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.
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.
In spite of what the American Diabetes Association (ADA) tells us, a truly normal A1c is between 4.6% and 5.3%
And 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.
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 every 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.
This study showed that even after a high-carb meal, normal people’s blood sugar rises to about 125 mg/dL for a brief period, with the peak blood sugar being measured at 45 minutes after eating, and then drops back under 100 mg/dL by the two hour mark.
Another continuous glucose monitoring study confirmed these results. 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.
Even the American Association of Clinical Endocrinologists is now recommending that post-meal blood sugars never be allowed to rise above 140 mg/dL. Unfortunately, less informed groups like the ADA haven’t caught up with the science.
The consequences of this are severe. Nerve damage occurs as blood sugar rises above 140 mg/dL. Prolonged exposure to blood sugars above 140 mg/dL causes irreversible beta cell loss (the beta cells produce insulin). 1 in 2 “pre-diabetics” get retinopathy, a 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)||<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 are only normal if you think increased risk of diabetes, heart disease, cancer and other serious complications is normal. Just because these conditions are common, doesn’t mean they’re normal.
If you’re interested in health and longevity – instead of just slowing the onset of serious disease by a few years – you’d be well advised to shoot for these targets instead:
|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 very reliable for predicting diabetes or CVD risk. Post-meal blood sugars are by far the most 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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Tags: a1c, blood, diabetes, fasting, glucose, hemoglobin, impaired, normal, sugar
K… Don’t know where or how old this info is. I’m work in pharmacy and just took a CEU on Diabetes that the info is good on for the next two yrs. Normal is 70-130 and a1c of 7%. So… wondering what source is being used for these statistics. You can view mine at wwww.powerpak.com look for the CEU on Diabetes.
Chris, this is some of your best work. My BF and I are two months into a low carb diet and my blood sugar has stabilized, but he still has extreme hunger between meals and has to eat 4x a day. Can’t wait for your third installment where you show how to check blood sugar between meals–I suspect he has some insulin issues that I don’t have.
Thank you so much for these incredibly well-written articles.
Great article. You mention that FBG can be elevated on a low carb diet. What do you consider a low carb diet to be in terms of grams? Anything under 150g a day or do you mean a keto diet?
I used to think LC was under 100 carbs also, but apparently the strict definition of LC is less than 130: http://livinlavidalowcarb.com/blog/?p=6648.
My BS is better on 120-150 carbs than it was on VLC, but I am wondering why my FBS is not ideal still,; though my PP numbers are where they need to be.
Any other thoughts on correcting IR? I read all your posts and I watch my carbs, eat a strict gluten free diet, limit vegtable oils (I have recently gone further and embraced an extremly low PUFA diet, so no more bacon etc. for me) and get good sleep. I also take metformin and natural thyroid.
Despite all of this, my insulin is never below the magic 10. Any ideas on what I can do?
Chris: if, as you state, “low-carb diets induce insulin resistance,” why isnt it a cause for concern? I went low carb some time ago, no processed foods or bad oils, lost 20 lbs, do regular strength and resistance training, A1c 5.3, post-prandials <120, usually <100, very low BMI and BFP.
But now my FBG levels are as high as 125! (Used to be 87) I guess I don't get the logic behind the assurances that a low-carb diet "may not be a cause for concern" when in the same article you quote studies showing diabetes risk in people with FBG levels above 95. Type II diabetes runs in my family, including those who are not overweight. Does someone like me need to be concerned? What are the botanicals and nutrients you refer to that can improve insulin sensitivity?
Thank you for doing this topic. I write a diabetes blog and I try not to club the ADA all the time but those guidelines always seem to pop up. They are a major problem because they give people a since of security that they shouldn’t have.
I was actually thinking about this just before I read your blog. I’m a type 2 ketosis prone diabetic with a family history of diabetes and because of this I view the ADA guidelines as nearly tragic for people like me. I’ve come to a decision that I’m going to tell people in my family what are the real guidelines for diabetes. Basically, I’m taking the FBS ADA guidelines and using them for everything. Less than 100 is normal. 100 to 120 is the prediabetic range and above 120 is diabetic. I know that sounds pretty drastic for postprandials and the like but I would rather my children and grandchildren have a chance for a healthy future.
I wrote a long blog on hemoglobin and A1c and put up charts of the people who are most likely to have these sorts of problem, whether they are diabetic or not. Interestingly enough, this seems to match up with peoples that live where Malaria or Malaria like diseases occur.
Just read your replies on Whole Health. Here’s something to test on people you know who spike easily. Give them a NSAID for two or three days. If their blood sugars cease to spike then it might be a glucose desensitization issue. The has to do with inhibiting COX-2 and PGE 2. I’m reporting on this on my blog.
Another great article, Chris. I’m puzzled by my FBS being around 95-99 but frequently my 2 hr post prandial will be below 90. Shouldn’t the FBS come in lower? Is this a morning cortisol stress response?
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!
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?
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?
Thanks, Chris, that’s encouraging. I’ll check out your site. I have learned a lot from your blog.
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?
Great! Thank you.
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?
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
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.
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.
Thanks Lynn, these conditions have killed my brain! Am looking forward to the next article, I’ll be picking up a monitor shortly.
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.
Also Jo, what conditions do you have?
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.
Peat is more gung ho anti PUFA’S than Stone is. A max of two eggs a day, olive oil only as a condiment and PUFA free meat such as beef and lamb.
When one increases carbs, it can expose hidden issues. Have you had a cortisol saliva test, a full thyroid panel (TSH, Free T4, and Free T3, anti-TPO, anti-TgAb and Reverse T3) and sex hormone panel done?
What are you basal temps? Temps during the day? Have you been to Stop The Thyroid Madness?
I saw a private endocrinologist in August and I think she asked for these tests, I had them done, but unfortunately I haven’t seen the results although I asked for them. She hasn’t said anything besides the fact that my LDL cholesterol is high. You would think she knows how to interpret them properly. She didn’t ask for a salivary cortisol test, so I’m just guessing there, from my experience. She doesn’t want to prescribe T3 as allegedly it is not licensed in Ireland.
Oh, my basal temperature was ok when I had a look at it in the morning but I’m freezing all the time especially at night when I go to bed late, however, very often it’s around 14 C in the house. I checked that website too.
Do you live in Ireland? Snap…..
It is ILLEGAL for her to withhold your test results. You need to speak to her secretary and demand them. If that fails, send a written letter to the records department, citing the Data Protection Act 1989. If nothing within a month, threaten them with legal action. Worked for me, because they knew that what they were doing was illegal.
T3 is available in Ireland yep. It’s not illegal.
Oh, hello there. Thank you for reminding me about the Data Protection Act.
Lynn, I have Hashi’s, IBS, diagnosed with fibro, not yet convinced as I have chronically high inflammatory markers and signs of lupus without the ANA, kidneys at stage 2, elevated liver enzymes etc. I’ve just changed doctors and he is redoing all tests, so I haven’t modified my diet yet as I wanted to have these results without changing anything (to help eliminate factors that may be causing symptoms), then going to reexamine diet.
Thank you so much for your response. Could a chronic aggravating pain, such as in a heel spur, possibly be responsible for the inbalance of cortisol and/or glucagon that causes the rise in blood sugar?
Once again, thank you.
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