My exercise-induced sugar levels


First post-run BG
When I started self-monitoring my blood glucose, I was a zealous tester, testing up to ten times a day. But I tested only for food and not for exercise. Testing for other things meant using more strips, which were not cheap, and pricking more times than my fingers could handle. In addition, I did not consider it necessary because exercise is crucial to controlling diabetes and lowering high post-meal BG level, which I thought meant that exercise automatically gobbled up my BG. But one blood test laid bare my ignorance.

One beautiful autumn day a few years ago, after a long run, I decided to test just to see how much my BG had decreased after that run. My fasting pre-run BG was around 120, I drank a small glass of chocolate soy milk before heading out, and I nibbled my favorite Clif Bar chocolate chip peanut crunch during the run, which meant that I had plenty of glucose coursing through my veins to meet my fueling needs. My naïve self envisioned my muscles gorging on all the glucose while I was running.

My then brand new gray UltraMini read 180 mg/dL. What? That can’t be right. I washed my hands and tested again. Similar number. I confirmed the accuracy of the meter and the strips with the control solution. After getting a similar number for the third time, it finally sank in that my post-run BG was indeed around 180. I freaked out. Subsequent tests also showed that skiing and even an hour of headbanging to Metallica music will raise my blood glucose.

You can imagine my confusion and disappointment. Why is my blood glucose high? How can my BG number climb when exercise promises lower insulin resistance and is supposed to bring high post-meal BG numbers down? If high BG increases my risk for diabetes complications, and my BG rises when I exercise, then is exercise bad for me? 

A sense of hopelessness came over me. Should I give up running, skiing and dancing in exchange for a near-normal BG level? As soon as I asked this question, however, my brain very quickly but most emphatically said, “That is not an option.”

What makes my BG rise
I now know that exercise, especially vigorous exercise, can cause my and other diabetics’ BG to rise. But how high hinges on several factors, such as what I’ve eaten the night before; whether, what and when I eat before or while exercising; level of exertion; how long I exercise; the time of day; even the weather. Here are a few of the possible permutations and resulting BG rises in absolute numbers (to keep it simple I’m listing only those related to running):

  • Easy, slow short or long runs; no food – 5 to 10
  • Steady runs or threshold runs; no food – 10 to 20
  • Hard runs; no food – 20 to 30
  • Short easy runs, with half a banana before or during – 20 to 35
  • Hard runs, with half a banana before or during – 30 to 40
  • Long runs, with half a banana before or during – 20 to 25
  • Short easy runs, or long runs, with 1 glass of chocolate soy milk before – over 30
  • Hard runs, with 1 glass of chocolate soy milk before – over 40
  • Long runs, with 1 Clif Bar during – over 40 points
  • Long runs, with 1 glass of chocolate soy milk before, and 1 Clif Bar during – over 60
  • Hot weather – add another 5 to 10 points

Why I still exercise
If you look at the numbers alone, they look scary, don’t they? But these numbers do not tell the whole story.

First of all, the BG number I may end up with does not have to be incredibly high. For example, if my pre-run number is 90, then a hard run on a hot day may raise that to 115 or 130, which I find acceptable.

Second, BG rises can be minimized (see last section below).

Third, the rise is short-lived, usually half an hour to an hour after exercising. What’s more, and this is important, my BG level generally stays low for the rest of the day, even if I eat slightly more carbs right after running (by this I mean, one slice of pain de campagne or an extra persimmon, not the entire bread basket or bag of potato chips). For example, for Saturday’s 70 minute moderate run, my pre-run BG (after a snack) was 117 and post-run was 144. After the run, my meal included a slice of tomato bread and fruits (I’m so into persimmons these days). Two hours later, my BG was 92 and stayed low for the next three hours.

I have, however, noticed one exception to this nice arrangement – my BG number remains high for a longer period, sometimes up to four hours, if I have chocolate soy milk or sports bar, gel or drink before, during or after exercising. I did not notice this trend early on, but noticed it only when I reduced my meds from metformin, amaryl and acarbose (all of which combined caused my after-exercise BG to drop like a stone), to just metformin. Hence, these food products are no longer part of my diet.

Fourth, overall, my BG is generally easier to control when I exercise regularly than when I am mostly inert. I am proof that regular exercise reduces insulin resistance.

Minimizing BG rises
Don’t think that I don’t worry about the risks of developing diabetes complications due to high BG levels. I worry, especially when I go to forums and read statements like “Temporary glucose spikes can lead to damage” written authoritatively by very assured people. Hence, I try to reduce exercise-related BG rises. How?

First, I condensed my observations to a few guidelines.

  1. My BG goes up if I exercise vigorously. It may go up, and perhaps only slightly, if I have slow, easy exercise rounds.
  2. My BG may go up if I consume some carbs before or while exercising.
  3. My BG will go up if I consume a lot of carbs, especially fast-acting processed ones, before or while exercising, or (if I exercise in the morning) the night before.
  4. The BG increase is higher, and lasts longer, if I consume fast-acting processed carbs.
  5. Exercising on a hot day, other than inside an air-conditioned room, will raise my BG.

Then, I formulated specific practical action items based on these guidelines. By the way, the guidelines and action items are not immutable and are subject to change to reflect changes in different aspects of my life. Listed below are a few examples of these action items. While most of these focus on running, I apply them to my other activities.

  • I do not carbo load.
  • I do not consume fast-digesting, -absorbing and -acting processed carbs before, during or after a run, even very long runs or races.
  • I do not eat or drink anything, other than water, before or during short runs.
  • I’ve recently trained myself to do longer runs on an empty stomach. But if I have to eat (say, I’m really hungry or during a race), I have yogurt or fruit.
  • For added energy or stamina, I rely on low carb electrolytes and supplements.
  • Unless I’m training for a race, I reduce hard runs.
  • On a hot day, I rest, do easy runs, or exercise earlier in the morning or around sunset.

The best way to avoid an unacceptably high exercise-induced BG number (short of quitting) is to maintain a BG level that is as close to a non-diabetic’s as possible. This means paying attention to what I eat and drink, taking my meds, avoiding stress, and exercising regularly; in other words, being in control of my diabetes. It’s an interesting concept: to keep my BG generally in check, I have to exercise; however, to minimize exercise-generated BG rises, I have to keep my BG generally in check. That’s a neat closed loop, isn’t it?


6 thoughts on “My exercise-induced sugar levels

  1. Phil Ruggiero


    I have noticed the same thing in my blood. I tested up to 5 or 6 times a day just because I wanted to understand more about my body. Like you, my glucose would go up after exercise and then come back down. What I found out was that was normal. Whew! And, like you, it takes a bit of time to come back down. But, the exercise – your running, my walking – makes it easier for insulin to get glucose out of our blood and where it belongs.

    For me, that is a wonderful trade-off and allows me to not have to take meds any longer.

    Keep running!

    Take care,

  2. Nishad

    I had similar experience with my post run BG as well. before run BG was 92 and after a 7 mile run BG was 140. When I visited my doctor and told him about it, he confirmed that it is possible. Since I was pushing my body hard during running, my body produced more glucose to fuel my body. Some of it was absorbed my muscles, but since I have an insulin resistant body, most of the excess glucose stayed in my blood. That explained the increase in BG. Since that day, I have never carb-loaded myself before a run. just 1 slice of bread before a 10 mile or HM is sufficient to take me to the finish line. I carry GU Gel or glucose tablets with me, but I never had to use then in between a run. Post run, I eat a 2 bananas, yoghurt, and still be confident that my BG may be high right now, but in the next 2 hours, I will be below 100. Since the muscles are tired after the run, they will continue to absorb the glucose and bring my BG down.

    I have been reading your posts for quite some time now, and I feel like sharing my own experiences. There are not a lot of diabetic runners here in India, and would like to inspire them with my stories. Thanks for the inspiration.

    1. runningwithoutsugar Post author

      Thank you for sharing and for dropping by. I hope you continue sharing your experiences. There are not enough Type 2 diabetic athletes in the online community. In fact, I don’t think there are enough Type 2 diabetic bloggers.

  3. alexxcollins

    This is a really interesting post. I have type 1 not type 2, but I think there is a lot of similarities – mainly insulin sensitivity. I test frequently – before and after eating, during exercise etc. I also find that my BG rises during intense exercise, but my blood sugar control and insulin sensitivity is much better in general when I’m doing lots of exercise. So in my experience – the more exercise the better!


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