Spikes when exercising

sw600 · Jan 24, 2023

Hi all, I am prediabetic and decided to get myself some libre sensors to see what's what. I meet the thin/fit profile, so 177cm/66kg, 46 years old. I have been hovering between the pre-and-not area 39-44 a1c for about 5 years. I usually do a lot of exercise (cycling ~10,000km per year) although the past 6 months have been much lower due to knackering my wrist last summer.

Anyhow, I quite often get spikes over 12 when exercising. I don't know if that has been the case all the time I have been 'pre', or just a recent development. This morning example, attached, 1 hour of medium to hard effort, no food beforehand (and ~200ml of 5% yoghurt when I got back, so nothing carby). Is this 'expected'? If so is it 'bad', or is it somehow OK because it's exercise? I rarely see over 10 from actual food.

I've been trying hard to do low carb the past couple of weeks, but over xmas I was in Mallorca and really shoving any old food down me while doing a lot of cycling (75-100km per day) and I never saw such big spikes then, presumably because my body was continually in deficit. does that mean I need to ride for 3 hours per day to stay healthy? I don't think my wife will like that, even if I would!

Problem with a CGM is that a bunch of stuff happens and it's difficult to interpret. It has been very useful for some things but I feel I'm not able to fully understand and it's seemingly random at times!

plantae · Jan 24, 2023

One possible explanation, especially considering you're not on insulin, is that when you exercise that a hormone called glucagon kicks in and releases glucose from your liver because of the increased activity therefore increasing your BSL. I'm a botanist, not a doctor, but it seems plausible because that's how homeostasis works. Edit: looking at the graph it seems like a big spike though compared to baseline but is 12 bad for you? Interesting

sw600 · Jan 24, 2023

Yes it’s the relative size of the spike that I’m concerned about. I do see 12 occasionally from food but not usually.

I understand the adrenaline and glucagon response a bit, so is this an example of liver dumping glucose but then the other regulatory systems not being able to manage it? Or does this happen to everyone and I should stop overthinking it?

It’s only an hour’s exercise, I don’t know how much the liver adds (too much by the looks of it) but it does return to normal eventually in longer rides.

plantae · Jan 24, 2023

To be honest I don't know. When I exercise my BSL goes down rapidly unless I eat beforehand, but I'm on insulin. I'm just trying to think of plausible explanations. Hopefully someone not on insulin can chime in. My bet is that it's the liver dumping glucose but, as said, I'm a botanist not a medical doctor. If I spiked to 12 my endo and diabetic nurse would think nothing of it (my libre alarm is set to 14), but your circumstances may be different

plantae · Jan 24, 2023

It's an interesting graph to me! I do hope someone with more expertise can provide a qualified explanation

Deleted member 527103 · Jan 24, 2023

Are you aware of limitations of the Libre?
The spike may not be as high as Libre is reporting (it tends to exaggerate highs) and, the sensor is new, it may be less accurate.

The effect of exercise on blood sugars is highly dependent on the type of exercise, the exertion from the exercise, the fitness of the person doing it and how their body reacts.
For example, one of my exercises is cycling:
- If I have a gentle cycle along a flat tow path with my friend, my levels are unaffected
- if I go for a race along country roads, my levels drop
- if I cycle up a steep hill against the wind on a rainy day, my levels will rise.

Freya's_dad · Jan 24, 2023

To me, and i am Type 2 and controlling it with diet and exercise, also a very keen cyclist.

When you exercise at a moderate pace, your body relies more upon fat as a source with some glucose, what they call "fat burning zone" or Zones 1 and 2, which is aerobic exercise.

When your body starts to work harder, and you get to a pace where you're breathing harder and heart rate increases, then you become more and more dependant solely on glucose/ glycogen as a source of fuel.

Reading your description above, you are not fuelling at all before the effort. So there is little freely available glucose in your bloodstream to fuel you. So especially if you are exercising at a "medium to hard effort" as you describe, your body needs that fuel and starts to then pull glycogen from the liver and those muscles not being used, to fuel the effort you are doing. This "dump" of glycogen is the spike you're seeing.

You have to remember that carbs are the best fuel for your body, despite all the keto diets and the like, your body is a carb burning machine when you exercise hard.

the best bit is that when you are exercising, you're giving your pancreas a break, your muscles are using the glucose in the bloodstream straight up and you aren't storing it.

I think the main issue is your trying to basically run a machine without any fuel. Despite being Type 2, don't be afraid of carbs, but at the right time. So 90-120 minutes before you cycle take on a good quality source of carbs, for me i do something like overnight oats (large oats, with a scoop of vanilla protein powder and chia seeds, soaked in almond milk overnight, then a dollop of greek yoghurt and some berries added before eating) or a few slices of good quality wholemeal toast with eggs or peanut butter.

That way, your body has good quality carbs in the bloodstream to start, and because you have taken on protein and fat with them, it will absorb slowly from the stomach in to the bloodstream and not cause a spike, and the body will have the fuel it needs

if your rides go over an hour, especially at higher heart rates, then again, don't be afraid to eat 30g of carbs every 30-45 minutes, so you continue to fuel the effort.

What we cannot do as Type 2 is "carb load" in the old way, where you would a big bowl of pasta night before.

What you are doing is effectively starving your body of the fuel it needs before, during and after the effort, so you're body is reliant on pulling those energy stores from your liver and some muscles to keep you going.

If you find that you finish a ride and you then feel starving the rest of the day, that is a clear sign you have been under-fuelled for the effort you've done.

Hope that makes some sort of sense, i have a tendency to ramble!?

I am a great believer that this "we are Type 2 therefore all carbs are bad" is wrong, simply sugars and carbs are bad, complex carbs like brown rice, when eaten in conjunction with quality fats and protein if you're exercising regularly are needed. if you don't fuel well, you will end up exhausted and ill.

What we need to do is "periodise" them around when we exercise. Plus exercise is the best thing we can do, when you get fitter, the systems of the body become more efficient including those that help us regulate blood sugar levels.

sw600 · Jan 24, 2023

In Response said:
Are you aware of limitations of the Libre?
The spike may not be as high as Libre is reporting (it tends to exaggerate highs) and, the sensor is new, it may be less accurate.

The effect of exercise on blood sugars is highly dependent on the type of exercise, the exertion from the exercise, the fitness of the person doing it and how their body reacts.
For example, one of my exercises is cycling:
- If I have a gentle cycle along a flat tow path with my friend, my levels are unaffected
- if I go for a race along country roads, my levels drop
- if I cycle up a steep hill against the wind on a rainy day, my levels will rise.

I will look into the accuracy or otherwise of the libre. Makes sense that as the amplitude rises so does the error.

sw600 · Jan 24, 2023

Freya's_dad said:
To me, and i am Type 2 and controlling it with diet and exercise, also a very keen cyclist.

When you exercise at a moderate pace, your body relies more upon fat as a source with some glucose, what they call "fat burning zone" or Zones 1 and 2, which is aerobic exercise.

When your body starts to work harder, and you get to a pace where you're breathing harder and heart rate increases, then you become more and more dependant solely on glucose/ glycogen as a source of fuel.

Reading your description above, you are not fuelling at all before the effort. So there is little freely available glucose in your bloodstream to fuel you. So especially if you are exercising at a "medium to hard effort" as you describe, your body needs that fuel and starts to then pull glycogen from the liver and those muscles not being used, to fuel the effort you are doing. This "dump" of glycogen is the spike you're seeing.

You have to remember that carbs are the best fuel for your body, despite all the keto diets and the like, your body is a carb burning machine when you exercise hard.

the best bit is that when you are exercising, you're giving your pancreas a break, your muscles are using the glucose in the bloodstream straight up and you aren't storing it.

I think the main issue is your trying to basically run a machine without any fuel. Despite being Type 2, don't be afraid of carbs, but at the right time. So 90-120 minutes before you cycle take on a good quality source of carbs, for me i do something like overnight oats (large oats, with a scoop of vanilla protein powder and chia seeds, soaked in almond milk overnight, then a dollop of greek yoghurt and some berries added before eating) or a few slices of good quality wholemeal toast with eggs or peanut butter.

That way, your body has good quality carbs in the bloodstream to start, and because you have taken on protein and fat with them, it will absorb slowly from the stomach in to the bloodstream and not cause a spike, and the body will have the fuel it needs

if your rides go over an hour, especially at higher heart rates, then again, don't be afraid to eat 30g of carbs every 30-45 minutes, so you continue to fuel the effort.

What we cannot do as Type 2 is "carb load" in the old way, where you would a big bowl of pasta night before.

What you are doing is effectively starving your body of the fuel it needs before, during and after the effort, so you're body is reliant on pulling those energy stores from your liver and some muscles to keep you going.

If you find that you finish a ride and you then feel starving the rest of the day, that is a clear sign you have been under-fuelled for the effort you've done.

Hope that makes some sort of sense, i have a tendency to ramble!?

I am a great believer that this "we are Type 2 therefore all carbs are bad" is wrong, simply sugars and carbs are bad, complex carbs like brown rice, when eaten in conjunction with quality fats and protein if you're exercising regularly are needed. if you don't fuel well, you will end up exhausted and ill.

What we need to do is "periodise" them around when we exercise. Plus exercise is the best thing we can do, when you get fitter, the systems of the body become more efficient including those that help us regulate blood sugar levels.

That's an interesting idea about needing some circulating carbs already, I see what you mean, I will try to test it out over the next couple of weeks. Trouble is, getting up at 5 to allow things to digest for a 6.30 ride! Especially at this time of year.

I am also going to test out some different carbs on longer rides and see what is best for maintaining a level. Also just interested to try riding until I hit the wall and see what the numbers look like. What number is the wall? I have done a couple of longer rides where I felt as if I was out of energy but glucose was still OK, so was just my legs being rubbish

Freya's_dad · Jan 25, 2023

That's an interesting idea about needing some circulating carbs already, I see what you mean, I will try to test it out over the next couple of weeks. Trouble is, getting up at 5 to allow things to digest for a 6.30 ride! Especially at this time of year.

Ultimately, you cannot run any engine on empty for very long. Riding fasted without any fuel on board is done by the pros for 2-3 hours, for mere mortals it is not recommended for more than an hour, and then only if you work in lower zone 1 and zone 2 heart rates, where body is predominantly using fat as a fuel (and that is the idea of fasted riding, to try and teach body to use fat more as a fuel, and why 80% of your cycling should be in those lower heart rates/ power zones)

Think about when you exercise as giving your pancreas a holiday, it is not having to work when you're exercising much, as your muscles and energy systems are just pulling glucose from the bloodstream direct. That is why you need a decent breakfast before to fuel the effort, then as a ride goes over an hour, you need to fuel the continuing effort at 30-90g of carbs per hour depending on intensity, otherwise you will run out of energy, and then after a ride of more than hour, take on a mix of decent protein and some complex good carbs, as the muscles will be depleted of their stored glycogen, so those carbs you take on then are absorbed in to muscles and liver for storage, not free floating in the bloodstream

You can be "low carb" just before, during and just after exercise, it is the bodies preferred fuel, despite the articles you read from keto athletes telling you they ran a marathon on a cooked breakfast.

If you don't fuel your exercise correctly, then you will just get tired, ill and compromise immune system after a while. Plus you won't get any fitter, and the whole point of exercise is to make the bodies various systems more efficient, including your blood glucose levels.

Best thing about Libre, is that you can use your own body like an experiment, and work out what is best for you to fuel the efforts you're doing, it will always be individual and a bit of trial and error at the start.

markpj31 · Feb 19, 2023

The liver pumps out more glucose into the blood stream during intense periods of exercise, it's just to fuel the extra demand in the muscles which is fine in somebody non-diabetic as the body manages it correctly, but a little all over the place in diabetics.

It happens post-lifting weights for me, but is pretty short-lived. In fact, after a short period my blood glucose tends to crash later on in the day.

KennyA · Feb 19, 2023

Yes,this happens to me with strenuous exercise (football). Not tested it via a libre but a fingerprick a few minutes after stopping will show elevated levels. I generally play having fasted for about 18hrs, so this rise is all via the liver. It returns to normal very quickly.

My understanding is that this is exactly how the system is supposed to work. Exercise, muscles need extra fuel, liver dumps fuel, muscles get fuel, exercise stops, no extra fuel needed, liver stops dumping fuel. I think it might be really interesting to see a libre readout from professional athletes - not aware of any?

Techlab2k · Feb 26, 2023

This thread is helping me understand a lot of what is going on. Bear with me, this is the short version.
After ignoring my T2 diagnosis for many years I was hit hard by neuropathy last November leaving me struggling to walk and falling as my toes stopped moving and it moved to my legs. Long story but decided that if I was going to have anything like a normal life I needed to do to something drastic. I stumbled across the Fast800 diet and cherry picked the key principles focusing on one aspect the book briefly covered - exercise. I opted for Apple fitness+ strength and hit exercises for their convenience. I have done a strength and HIIT daily. Within 2 months I was down over a stone and rapidly developing muscle. Thinking I’m well on the way, having reversed 90% of the neuropathy I noticed that my fasting sugars were massively high. Starting the day with 3+ miles walk then the strength and HIIT then measuring BG I was getting 30+ mmol readings and in some cases my gadget was saying high! I was happy just consuming 1200 calories a day. I was burning visible body fat at an amazing rate, I would liken this to (sorry for the visuals here) about 2 pint glasses of fat a day. I then had the idea of slowing down the fat loss to reduce my BG so increased my calorie intake to 2000 a day and overnight my sugars dropped into a range of about 4.3 to 6.6 overnight. It’s here that my limited brain came to the conclusions broadly similar to all the sage advice above. I started this morning with a protein shake but my sugars after my walk were 10.4 opposed to my 5.6 waking up. Thanks to these wise words pointing to good carbs I’m getting up early for porridge before I exercise and see what happens. I’m guessing about 30 minutes between eating and exercise? I think that timing might be useful to plan with in the future. But let’s face it, 4 months ago my BG was 16+ first thing and 24+ two hours post prandial. That’s now 4.5 and 6.6 on average now and I know without testing that, before my evening meal they will be back at my fasting levels from first thing. Thanks again for the advice in this thread.

Techlab2k · Feb 27, 2023

Darn, didn’t work as I would have hoped. I normally get a drop in BG after my 3.5 mile walk then the spike shortly after. Today I started unusually high on 8.5 fasting. Small amount of porridge fruit and yoghurt and off on the walk. Slower round than usual and feeling fatigued at the half way. Picked up towards the end though. Came back in and BG at a massive 12.4. Feeling fuzzy headed with the extra sugar. I’ve just done 30min dumbbells and it’s falling down through 9 now. I think my walk isn’t strenuous enough to warrant the extra carbs but it was worth a try. I will be dusting the mountain bike off in the coming weeks and will see if it works out better doing that. For some reason I get better results, on the walk at least, not eating prior and only eating after all my exercise is done. The change in numbers is around 2mmol doing it that way unlike the 4 today.

sw600 · Feb 27, 2023

I tried the 'breakfast carbs to avoid spike' method too, with no benefit. Still a spike to 13ish. It's strange that the worst spikes I get are from exercise, not food.

@KennyA The data that was shared from a guy on the the Super Sapiens forum showed him hitting almost 10 during exercise, so it does happen to 'normal' people, at least to a certain extent.

See my data below from yesterday. Small amount of porridge with dash of maple syrup, from 6 > 13. Once exercising and the initial spike has worn off, a couple of hours later a gel with 40g carbs only raises it by a couple of points, same thing happens with further food during that ride (around 6 hours in total).

Slugger · Mar 2, 2023

Do you always go riding at a similar time of day? Do you get up at the same time even if not riding and do you have a similar spike? Maybe it's just the dawn phenomenon.

I'm on insulin and had always taken the same carb related dose before breakfast as any other time of day but a few months ago found that I had started getting spikes in the morning to the point of now having to take 2-3 times the normal dose before breakfast and still having to take insulin even if I skip breakfast. I get these spike roughly from the point of getting out of bed regardless of the time or activity.

Ekt53 · Mar 2, 2023

Freya's_dad said:
To me, and i am Type 2 and controlling it with diet and exercise, also a very keen cyclist.

When you exercise at a moderate pace, your body relies more upon fat as a source with some glucose, what they call "fat burning zone" or Zones 1 and 2, which is aerobic exercise.

When your body starts to work harder, and you get to a pace where you're breathing harder and heart rate increases, then you become more and more dependant solely on glucose/ glycogen as a source of fuel.

Reading your description above, you are not fuelling at all before the effort. So there is little freely available glucose in your bloodstream to fuel you. So especially if you are exercising at a "medium to hard effort" as you describe, your body needs that fuel and starts to then pull glycogen from the liver and those muscles not being used, to fuel the effort you are doing. This "dump" of glycogen is the spike you're seeing.

You have to remember that carbs are the best fuel for your body, despite all the keto diets and the like, your body is a carb burning machine when you exercise hard.

the best bit is that when you are exercising, you're giving your pancreas a break, your muscles are using the glucose in the bloodstream straight up and you aren't storing it.

I think the main issue is your trying to basically run a machine without any fuel. Despite being Type 2, don't be afraid of carbs, but at the right time. So 90-120 minutes before you cycle take on a good quality source of carbs, for me i do something like overnight oats (large oats, with a scoop of vanilla protein powder and chia seeds, soaked in almond milk overnight, then a dollop of greek yoghurt and some berries added before eating) or a few slices of good quality wholemeal toast with eggs or peanut butter.

That way, your body has good quality carbs in the bloodstream to start, and because you have taken on protein and fat with them, it will absorb slowly from the stomach in to the bloodstream and not cause a spike, and the body will have the fuel it needs

if your rides go over an hour, especially at higher heart rates, then again, don't be afraid to eat 30g of carbs every 30-45 minutes, so you continue to fuel the effort.

What we cannot do as Type 2 is "carb load" in the old way, where you would a big bowl of pasta night before.

What you are doing is effectively starving your body of the fuel it needs before, during and after the effort, so you're body is reliant on pulling those energy stores from your liver and some muscles to keep you going.

If you find that you finish a ride and you then feel starving the rest of the day, that is a clear sign you have been under-fuelled for the effort you've done.

Hope that makes some sort of sense, i have a tendency to ramble!?

I am a great believer that this "we are Type 2 therefore all carbs are bad" is wrong, simply sugars and carbs are bad, complex carbs like brown rice, when eaten in conjunction with quality fats and protein if you're exercising regularly are needed. if you don't fuel well, you will end up exhausted and ill.

What we need to do is "periodise" them around when we exercise. Plus exercise is the best thing we can do, when you get fitter, the systems of the body become more efficient including those that help us regulate blood sugar levels.

This is very interesting as I am pre-diabetic or diabetic depending on how one defines it - your point in the 7th paragraph of not being afraid of carbs is very true. Ive found that when doing two or three HIT exercises and two weight training sessions (upper body and lower body on separate days, in a week, taking in some carbs really helps avoiding a spike and/or a feeling of faintness or dizziness. Following a low carb diet too rigidly I found to be counter productive so now, like you I take some carbs and protein before exercise and have a protein/carb powder after exercise. This works well for me. On other thing not directly related to diet is the 'rest' times between exercises, say 60 to 90 secs is also crucial to proper recovery. Thank you for a very positive post.

sw600 · Mar 2, 2023

Slugger said:
Do you always go riding at a similar time of day? Do you get up at the same time even if not riding and do you have a similar spike? Maybe it's just the dawn phenomenon.

I'm on insulin and had always taken the same carb related dose before breakfast as any other time of day but a few months ago found that I had started getting spikes in the morning to the point of now having to take 2-3 times the normal dose before breakfast and still having to take insulin even if I skip breakfast. I get these spike roughly from the point of getting out of bed regardless of the time or activity.

Yes quite possibly it's worse in the mornings, I don't have enough data to be able to compare at the moment. My last sensor just ran out, I need to buy a couple more. Problem is there aren't that many times of the day I can fit in 6 hours on the bike and also see the rest of the family

Enuj · Mar 2, 2023

Freya's_dad said:
Ultimately, you cannot run any engine on empty for very long. Riding fasted without any fuel on board is done by the pros for 2-3 hours, for mere mortals it is not recommended for more than an hour, and then only if you work in lower zone 1 and zone 2 heart rates, where body is predominantly using fat as a fuel (and that is the idea of fasted riding, to try and teach body to use fat more as a fuel, and why 80% of your cycling should be in those lower heart rates/ power zones)

Think about when you exercise as giving your pancreas a holiday, it is not having to work when you're exercising much, as your muscles and energy systems are just pulling glucose from the bloodstream direct. That is why you need a decent breakfast before to fuel the effort, then as a ride goes over an hour, you need to fuel the continuing effort at 30-90g of carbs per hour depending on intensity, otherwise you will run out of energy, and then after a ride of more than hour, take on a mix of decent protein and some complex good carbs, as the muscles will be depleted of their stored glycogen, so those carbs you take on then are absorbed in to muscles and liver for storage, not free floating in the bloodstream

You can be "low carb" just before, during and just after exercise, it is the bodies preferred fuel, despite the articles you read from keto athletes telling you they ran a marathon on a cooked breakfast.

If you don't fuel your exercise correctly, then you will just get tired, ill and compromise immune system after a while. Plus you won't get any fitter, and the whole point of exercise is to make the bodies various systems more efficient, including your blood glucose levels.

Best thing about Libre, is that you can use your own body like an experiment, and work out what is best for you to fuel the efforts you're doing, it will always be individual and a bit of trial and error at the start.

Thank you, just got off my bike - explains a lot

EricW2004 · Mar 3, 2023

sw600 said:
Hi all, I am prediabetic and decided to get myself some libre sensors to see what's what. I meet the thin/fit profile, so 177cm/66kg, 46 years old. I have been hovering between the pre-and-not area 39-44 a1c for about 5 years. I usually do a lot of exercise (cycling ~10,000km per year) although the past 6 months have been much lower due to knackering my wrist last summer.

Anyhow, I quite often get spikes over 12 when exercising. I don't know if that has been the case all the time I have been 'pre', or just a recent development. This morning example, attached, 1 hour of medium to hard effort, no food beforehand (and ~200ml of 5% yoghurt when I got back, so nothing carby). Is this 'expected'? If so is it 'bad', or is it somehow OK because it's exercise? I rarely see over 10 from actual food.

I've been trying hard to do low carb the past couple of weeks, but over xmas I was in Mallorca and really shoving any old food down me while doing a lot of cycling (75-100km per day) and I never saw such big spikes then, presumably because my body was continually in deficit. does that mean I need to ride for 3 hours per day to stay healthy? I don't think my wife will like that, even if I would!

Problem with a CGM is that a bunch of stuff happens and it's difficult to interpret. It has been very useful for some things but I feel I'm not able to fully understand and it's seemingly random at times!

Hi, I'm type 1 and I box. The training is super intense. From time to time I get spikes like the one you describe. It's a spike I only get when exercising. It goes up very high very fast and then comes down again. What I've also noticed is that when the training becomes a habit the spikes stop, also they don't happen if my blood sugar is 6 or below before I start training. I rationalise this as follows. The spike is the result of a release of sugar from the liver. Once the exercise becomes routine, maybe the liver gets used to it and doesn't pump out the sugar. If I have been running with low or around 5-6 blood sugars for a while then the liver is depleted and it can't send out enough sugar to cause a spike. I'm no expert by the way, just sharing my experience and ideas, please, informed people, tell me if I'm talking nonsense.

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