Excellent article. I’m an athlete and the phenomenon I am dealing with is normal fasting glucose(85) , low insulin (2.5), but high A1C (6.2). I’ve searched high and low to understand this and doctor says “I’m fine”…. Would love help in understanding why markers don’t always align.l and how this makes sense.
I look at Type 2 Diabetes as not a “sugar” problem but actually a chronic excess storage problem.
In reality glucose is the last “marker” to rise in a true type 2 diabetic. They have many other markers rise before glucose including fasting insulin, triglycerides, Leptin and organ markers (liver function tests). They also have decreasing Adiponectin over time.
So fasting glucose is a not so great marker to diagnose diabetes.
I still want a better explanation though of A1C rise in people without diabetes. Just healthier rbcs isn’t enough of an explanation.
Well trained athlete, 650-700 annual hours of exercise, 55 yo, ~40 min 10k runner.
You might want to have your athletic populations check their fasted glucose "out of bed" vs their lab values.
My last two lab tests were 103/104 mg/dL, fasted. My doc wasn't concerned for the reasons you outline in your article.
I do a lot of blood lactate testing and noticed it was rising when I woke up, even when I didn't eat. Because of the link between lactate and glucose, I was curious if my glucose was rising out of bed too.
So I tested glucose manually (not CGM) ten mornings in a row, right out of bed. Result was an average of 90.5 mg/dL.
Based on your article (thanks) I gave myself a glucose tolerance test. Results were 87/158/99 mg/dL at 0/60/120 minutes.
Main thing I wanted to pass along was something we've seen with athletes and lactate. Make sure baseline is baseline.
Thanks for all your articles, they've been informative and helpful.
Hey Dr Guess, really interesting topic! I recently got into endurance sports myself and I didn't realise the medical profession would classify me as an athlete (I train 10 hours a week). I associate athlete with elite performers which I guess is wrong!
I'd question that athletes have good diets. Male marathon runners have worse atherosclerosis than matched non athlete controls (https://pubmed.ncbi.nlm.nih.gov/30323509/). That signals a poor diet.
The big fashion in endurance sports is gels loaded with sugar/glucose/high GI carbs. Taking those on every session. Most recreational athletes also train at their lactate threshold (LT1 or LT2) which is stressful for the autonomic system. Stephen Seiler's done the research by looking at training diaries. They tend to have an average higher intensity per session (https://twitter.com/StephenSeiler/status/1019857874133180416) & do not train at a sufficiently low intensity to build their aerobic base which improves mitochondrial function and the ability to metabolise fatty acids.
This leads to them being "sugar burners" even gym rats and moderately healthy people. See San Milan's paper here on p5 for charts on fatox between elite athletes, weekend warriors and sedentary people (https://escholarship.org/content/qt5cz1v976/qt5cz1v976.pdf).
So I wonder if an athletic population that was eating well (little atherosclerosis, low sat fat, whole food/med diet) & had a better intensity distribution (80% of training before the first lactate turn point, 20% more intense) would be healthier.
Please keep the articles coming, loving reading insights from a "non influencer" and someone who practices!
It's true that one of the new focuses in endurance sports is taking in lots of carbs. Like over 60g of carbs per hour, every hour, up to 90 or perhaps more. However, those are targeted at long, intense training sessions or races. A lot of the cyclists I hang on forums with are resistant to those recommendations, saying that it's a huge amount of carbs. I would be surprised if it truly is a big fashion, as in the general population of endurance sports is taking in 60+g of carbs an hour.
As measured by a power meter, I can burn 800 or more calories in a 75-90 minute, intense interval session on the trainer, at the intensity levels where they recommend lots of carbs. I can burn 1500+ calories on a 3-hour group ride, where the intensity is generally lower than where you'd want a high carb intake.
(NB: technically power meters measure the power output at the bicycle's cranks, not the energy expended by the body to turn the bicycle's cranks. You do have to assume the body's gross mechanical efficiency to get from work done to calories burnt; this has been measured in trained cyclists, and it averages about 21% but I forget the standard deviation. So the calorie estimates should have a range around them, but it's more accurate than estimating calories from heart rate.)
“So I wonder if an athletic population that was eating well (little atherosclerosis, low sat fat, whole food/med diet) & had a better intensity distribution (80% of training before the first lactate turn point, 20% more intense) would be healthier.”
This is 100% me and I still have the discrepancy in numbers Dr Guess described: Good fasting glucose, lipids, insulin and ‘prediabetic’ A1c. There is something still to be explored with this. My current hypothesis is that people who train 10+ hours per week are presenting the body w a persistent *demand* for glucose to fuel training and recovery and that is why the average supply of available glucose is ‘high’, whereas in T2D the average availability of glucose is high because of the inability to store the amount input by diet and sedentary lifestyle choices. Does anyone have thoughts about this idea?
the atherosclerosis thing in athletes is much more complicated than you wrote. The medical litterature is not even clear if there is more atherosclerosis or not. Imaging studies show elevation of CAC scores but we don't know if it's gonna impact the prognosis in a bad way.
I do alot of easy training, have been aware of Dr Seilers work for years, I sometimes do experiences with a CGM and a lactate meter, eat clean, gels are only for races... and I also have this slightly elevated HBA1C
Could you cite any studies on the medical literature? I’m aware they are more stable, harder less likely to cause issues but it’s still an increased risk.
To clarify, you speak about atherosclerosis and coronary diseases or more broadly of the effects of a lot of endurance sports on the heart ?
There a pro and cons cardiologists so the debate is not finite, best articles are from BD Levine, Eijsvogels and La Gerche. I feel like James O'Keefe is quite fear mongering and ends up in some kind of academic conflict with his topic of acceleration of atherosclerosis. Maybe it's just me trying to escape a bad faith ;) but frankly it's not *that* clearcut.
The more optimistic is Levine saying that their data from the CCLS are reassuring if I recall correctly.
I'm so glad I found your post! I'm in just the situation you describe, and I'm about to meet with my doctor to discuss these confusing results (slightly elevated fasting glucose and H1AC, low fasting insulin, and normal post-prandial glucose response). I was getting worried that maybe I was headed toward adult-onset Type 1 diabetes, but maybe it's just that I'm an athlete on a relatively low carbohydrate diet :)
I found your blog after hearing exactly what you are writing about. I’m 67 years old, do one SIT run session every five days and two 4x4 HIIT run sessions per week. Add to that biking and resistance training, slim body, and good diet. So my A1C came in at 5.9 and fasting glucose at 106. Three days prior I completed a 10K race and came in third in my age group. So, your blog was very reassuring. Thank you so much.
Just some constructive feedback: while you explained why post prandial glucose is generally normal, it doesn’t appear that you clearly explained HOW/WHY a slightly elevated fasting glucose in athletes comes to be.
Additionally it would help extremely helpful to use both standard and metric units (mmol/L to mg/dL) for us Americans. I had a conversion calculator opened in a second tab while reading your article :)
Interesting read. I found myself here because I’m trying to understand biochemistry. I’m 43, runner (30mi/week), BMI at 23.4 and A1C 6.4%. As a neurobiologist, I’m totally confused.
The elephant in the room, is the amount of CARBS athletes allows themselves between trainings, because they are "athletes". Even if they don't gulp down sugary drinks and cakes, and rather choose "healthy" options, like oats, rice or potatoes and such, they tend to subject themselves to high intake of glucose, when they rely on insulin to shunt it away from the blood. Even if they are insulin sensitive, a spike of 180mg/dL might be an issue (glycation).
I think, too many athletes assume their glycogen stores are more depleted than they actually are, and overestimate the amount needed to have sufficient amounts of glycogen for effective training. They see their watch claiming they spent a 1000 calories on their zone 2 run, and then proceeds to get at least 250g of carbs back in. Totally disregarding, that since it was a zone 2 run, it was probably 600 calories from fat and only 400 from carbs (about the 2 Maurten 100 gels they had during the run, right?).
For an athlete, fasting glucose is about as relevant as the color of your valve caps on your car, and OGTT is as well. Average glucose, if you are wearing a CGM, is far more relevant, and so if the number and magnitude of glucose spikes..
The usual keto/low carb enthusiasts are certain it's because we are getting too much carbs. But I started before gels had been invented and don't use any sports 'nutrition' products except in long races, once or twice a year. My daily diet is not high in carbs. So I'm pretty sure that is not it.
Sorry I forgot to ask you in my comment about filip Larsens' work on some timeframes of insuline resistance in athletes, might be something to add too ?
Your article popped up in my timeline when I was searching for info on endurance athletes and HBA1C after viewing the latest Lionel Sanders (pro triathlete) on YT complaining about his HBA1C of 5.9%
On my side, as an 44 yo amateur endurance athelete (10h/wk), mine is 5.7 with fasting insulin level of 3,4 mUI/ml and my fasting plasma glucose of 3.3 mmol/l I guess it's my post-prandial plasma glucose that might elevate the HBA1C, your blog post taught me something super interesting !
This is gold!! I got hospitalized with walking Pneumonia for 3 days 15 months ago and they told me I was prediabetic and having a heart attack 😂 etc. I told them it was impossible. My numbers were 100% normal as I had just completed a research study and gotten all my numbers. I tried a GP from Kaiser and she was having none of it so I walked out and never returned. It’s hard to find a doctor who knows how to work with former athletes who still live the athlete lifestyle.
Hi! When you say that in someone with slightly elevated fasting glucose you’d expect a similar slightly elevated post prandial measurement, but these athletes don’t have that, can you explain how they react? So if their fasting is 105, after a meal it rises to 135 or even 140 or 145 but comes down (maybe not all the way to 105 but around 110 or so) after two hours, is that what you are referring to, or would you consider a person with this response to also have too high of a post prandial response?
This is the first article I have ever found that talks about this. I feel like I'm an anomaly that my doctors don't know what to do with. My A1C is above normal (pre-diabetic) but with no other significant makers. (Low insulin, good insulin sensitivity, active, good body weight, non smoker/drinker). I did fine on Glucose Tolerance Test but I was wearing a CGM and my spike came down for the blood draw but then popped back up again, which is how I react to any carbs (multiple spikes). I would love to find an endocrinologist or a doctor who could either clear me or tell me what is going on.
Excellent article. I’m an athlete and the phenomenon I am dealing with is normal fasting glucose(85) , low insulin (2.5), but high A1C (6.2). I’ve searched high and low to understand this and doctor says “I’m fine”…. Would love help in understanding why markers don’t always align.l and how this makes sense.
Thank you. Well written and researched.
I look at Type 2 Diabetes as not a “sugar” problem but actually a chronic excess storage problem.
In reality glucose is the last “marker” to rise in a true type 2 diabetic. They have many other markers rise before glucose including fasting insulin, triglycerides, Leptin and organ markers (liver function tests). They also have decreasing Adiponectin over time.
So fasting glucose is a not so great marker to diagnose diabetes.
I still want a better explanation though of A1C rise in people without diabetes. Just healthier rbcs isn’t enough of an explanation.
Well trained athlete, 650-700 annual hours of exercise, 55 yo, ~40 min 10k runner.
You might want to have your athletic populations check their fasted glucose "out of bed" vs their lab values.
My last two lab tests were 103/104 mg/dL, fasted. My doc wasn't concerned for the reasons you outline in your article.
I do a lot of blood lactate testing and noticed it was rising when I woke up, even when I didn't eat. Because of the link between lactate and glucose, I was curious if my glucose was rising out of bed too.
So I tested glucose manually (not CGM) ten mornings in a row, right out of bed. Result was an average of 90.5 mg/dL.
Based on your article (thanks) I gave myself a glucose tolerance test. Results were 87/158/99 mg/dL at 0/60/120 minutes.
Main thing I wanted to pass along was something we've seen with athletes and lactate. Make sure baseline is baseline.
Thanks for all your articles, they've been informative and helpful.
Gordo
Hey Dr Guess, really interesting topic! I recently got into endurance sports myself and I didn't realise the medical profession would classify me as an athlete (I train 10 hours a week). I associate athlete with elite performers which I guess is wrong!
I'd question that athletes have good diets. Male marathon runners have worse atherosclerosis than matched non athlete controls (https://pubmed.ncbi.nlm.nih.gov/30323509/). That signals a poor diet.
The big fashion in endurance sports is gels loaded with sugar/glucose/high GI carbs. Taking those on every session. Most recreational athletes also train at their lactate threshold (LT1 or LT2) which is stressful for the autonomic system. Stephen Seiler's done the research by looking at training diaries. They tend to have an average higher intensity per session (https://twitter.com/StephenSeiler/status/1019857874133180416) & do not train at a sufficiently low intensity to build their aerobic base which improves mitochondrial function and the ability to metabolise fatty acids.
This leads to them being "sugar burners" even gym rats and moderately healthy people. See San Milan's paper here on p5 for charts on fatox between elite athletes, weekend warriors and sedentary people (https://escholarship.org/content/qt5cz1v976/qt5cz1v976.pdf).
So I wonder if an athletic population that was eating well (little atherosclerosis, low sat fat, whole food/med diet) & had a better intensity distribution (80% of training before the first lactate turn point, 20% more intense) would be healthier.
Please keep the articles coming, loving reading insights from a "non influencer" and someone who practices!
It's true that one of the new focuses in endurance sports is taking in lots of carbs. Like over 60g of carbs per hour, every hour, up to 90 or perhaps more. However, those are targeted at long, intense training sessions or races. A lot of the cyclists I hang on forums with are resistant to those recommendations, saying that it's a huge amount of carbs. I would be surprised if it truly is a big fashion, as in the general population of endurance sports is taking in 60+g of carbs an hour.
As measured by a power meter, I can burn 800 or more calories in a 75-90 minute, intense interval session on the trainer, at the intensity levels where they recommend lots of carbs. I can burn 1500+ calories on a 3-hour group ride, where the intensity is generally lower than where you'd want a high carb intake.
(NB: technically power meters measure the power output at the bicycle's cranks, not the energy expended by the body to turn the bicycle's cranks. You do have to assume the body's gross mechanical efficiency to get from work done to calories burnt; this has been measured in trained cyclists, and it averages about 21% but I forget the standard deviation. So the calorie estimates should have a range around them, but it's more accurate than estimating calories from heart rate.)
english readers can translate this note https://nfkb.substack.com/p/jouons-avec-les-chiffres for a bit of fun with powermeter and calories :)
“So I wonder if an athletic population that was eating well (little atherosclerosis, low sat fat, whole food/med diet) & had a better intensity distribution (80% of training before the first lactate turn point, 20% more intense) would be healthier.”
This is 100% me and I still have the discrepancy in numbers Dr Guess described: Good fasting glucose, lipids, insulin and ‘prediabetic’ A1c. There is something still to be explored with this. My current hypothesis is that people who train 10+ hours per week are presenting the body w a persistent *demand* for glucose to fuel training and recovery and that is why the average supply of available glucose is ‘high’, whereas in T2D the average availability of glucose is high because of the inability to store the amount input by diet and sedentary lifestyle choices. Does anyone have thoughts about this idea?
hello
the atherosclerosis thing in athletes is much more complicated than you wrote. The medical litterature is not even clear if there is more atherosclerosis or not. Imaging studies show elevation of CAC scores but we don't know if it's gonna impact the prognosis in a bad way.
I do alot of easy training, have been aware of Dr Seilers work for years, I sometimes do experiences with a CGM and a lactate meter, eat clean, gels are only for races... and I also have this slightly elevated HBA1C
Could you cite any studies on the medical literature? I’m aware they are more stable, harder less likely to cause issues but it’s still an increased risk.
another recent interesting read : https://doi.org/10.1093/eurheartj/ehae927
To clarify, you speak about atherosclerosis and coronary diseases or more broadly of the effects of a lot of endurance sports on the heart ?
There a pro and cons cardiologists so the debate is not finite, best articles are from BD Levine, Eijsvogels and La Gerche. I feel like James O'Keefe is quite fear mongering and ends up in some kind of academic conflict with his topic of acceleration of atherosclerosis. Maybe it's just me trying to escape a bad faith ;) but frankly it's not *that* clearcut.
The more optimistic is Levine saying that their data from the CCLS are reassuring if I recall correctly.
Edit : quick check found this article : https://jamanetwork.com/journals/jamacardiology/fullarticle/2722746
I'm so glad I found your post! I'm in just the situation you describe, and I'm about to meet with my doctor to discuss these confusing results (slightly elevated fasting glucose and H1AC, low fasting insulin, and normal post-prandial glucose response). I was getting worried that maybe I was headed toward adult-onset Type 1 diabetes, but maybe it's just that I'm an athlete on a relatively low carbohydrate diet :)
I found your blog after hearing exactly what you are writing about. I’m 67 years old, do one SIT run session every five days and two 4x4 HIIT run sessions per week. Add to that biking and resistance training, slim body, and good diet. So my A1C came in at 5.9 and fasting glucose at 106. Three days prior I completed a 10K race and came in third in my age group. So, your blog was very reassuring. Thank you so much.
Thanks for your helpful article.
Just some constructive feedback: while you explained why post prandial glucose is generally normal, it doesn’t appear that you clearly explained HOW/WHY a slightly elevated fasting glucose in athletes comes to be.
Additionally it would help extremely helpful to use both standard and metric units (mmol/L to mg/dL) for us Americans. I had a conversion calculator opened in a second tab while reading your article :)
Thanks!!
could you define better the volume/intensity that would qualify one as an athlete as the concept is used in this post?
Interesting read. I found myself here because I’m trying to understand biochemistry. I’m 43, runner (30mi/week), BMI at 23.4 and A1C 6.4%. As a neurobiologist, I’m totally confused.
The elephant in the room, is the amount of CARBS athletes allows themselves between trainings, because they are "athletes". Even if they don't gulp down sugary drinks and cakes, and rather choose "healthy" options, like oats, rice or potatoes and such, they tend to subject themselves to high intake of glucose, when they rely on insulin to shunt it away from the blood. Even if they are insulin sensitive, a spike of 180mg/dL might be an issue (glycation).
I think, too many athletes assume their glycogen stores are more depleted than they actually are, and overestimate the amount needed to have sufficient amounts of glycogen for effective training. They see their watch claiming they spent a 1000 calories on their zone 2 run, and then proceeds to get at least 250g of carbs back in. Totally disregarding, that since it was a zone 2 run, it was probably 600 calories from fat and only 400 from carbs (about the 2 Maurten 100 gels they had during the run, right?).
For an athlete, fasting glucose is about as relevant as the color of your valve caps on your car, and OGTT is as well. Average glucose, if you are wearing a CGM, is far more relevant, and so if the number and magnitude of glucose spikes..
thank you, this is helpful.
I'm 65, competitive swimmer, runner and triathlete since 1970, average 5-8 hours of intense exercise each week. Also prediabetic since the age of 50.
Alex Hutchinson had a good overview,
https://www.outsideonline.com/2201466/are-endurance-athletes-more-susceptible-getting-diabetes
The usual keto/low carb enthusiasts are certain it's because we are getting too much carbs. But I started before gels had been invented and don't use any sports 'nutrition' products except in long races, once or twice a year. My daily diet is not high in carbs. So I'm pretty sure that is not it.
Sorry I forgot to ask you in my comment about filip Larsens' work on some timeframes of insuline resistance in athletes, might be something to add too ?
Very very interesting !
Your article popped up in my timeline when I was searching for info on endurance athletes and HBA1C after viewing the latest Lionel Sanders (pro triathlete) on YT complaining about his HBA1C of 5.9%
On my side, as an 44 yo amateur endurance athelete (10h/wk), mine is 5.7 with fasting insulin level of 3,4 mUI/ml and my fasting plasma glucose of 3.3 mmol/l I guess it's my post-prandial plasma glucose that might elevate the HBA1C, your blog post taught me something super interesting !
This is gold!! I got hospitalized with walking Pneumonia for 3 days 15 months ago and they told me I was prediabetic and having a heart attack 😂 etc. I told them it was impossible. My numbers were 100% normal as I had just completed a research study and gotten all my numbers. I tried a GP from Kaiser and she was having none of it so I walked out and never returned. It’s hard to find a doctor who knows how to work with former athletes who still live the athlete lifestyle.
Hi! When you say that in someone with slightly elevated fasting glucose you’d expect a similar slightly elevated post prandial measurement, but these athletes don’t have that, can you explain how they react? So if their fasting is 105, after a meal it rises to 135 or even 140 or 145 but comes down (maybe not all the way to 105 but around 110 or so) after two hours, is that what you are referring to, or would you consider a person with this response to also have too high of a post prandial response?
This is the first article I have ever found that talks about this. I feel like I'm an anomaly that my doctors don't know what to do with. My A1C is above normal (pre-diabetic) but with no other significant makers. (Low insulin, good insulin sensitivity, active, good body weight, non smoker/drinker). I did fine on Glucose Tolerance Test but I was wearing a CGM and my spike came down for the blood draw but then popped back up again, which is how I react to any carbs (multiple spikes). I would love to find an endocrinologist or a doctor who could either clear me or tell me what is going on.