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High blood sugar after exercise?

June 26, 2015 by Scott Johnson

From Markus Berndt: It’s one of the first recommendations you get after being diagnosed with diabetes. “Get active, do more exercise, it’s good for you!” And since we’ve been a child we’ve heard that exercise is healthy. If we do it consistently we’re rewarded, literally, with an awesome beach body.

Adding exercise into our day is also good for our diabetes. We’re taught that exercise lowers blood sugar, right? But can the opposite also be true? Can you have high blood sugar after exercise?

Up close

We now know that physical activity usually lowers blood sugar because it reduces how much insulin is needed to move sugar into the cells.

While, in the past, most experts advised frequent training intervals at moderate intensity, but recent studies have shown that even short, intense workouts are very effective. For example, a 15-minute intense weight training lowered blood sugar even more than what’s seen in some endurance training.

So activity lowers blood sugar – but not always!

Personally, I experienced this very early on and was extremely irritated! I just learned that exercise lowers blood sugar, but an intense 45-minute run consistently resulted in higher blood sugars than when I started! What in the world?

At first, I was confused and felt like I didn’t understand the world anymore. Then it was more of a “would you look at this?” kind of thing. And finally, I was determined to figure out what was happening. I knew there had to be an explanation.

Why does exercise sometimes raise blood sugar?

Exercise can trigger the body to release stress hormones, like adrenaline which stimulates the liver to release glucose or cortisol which makes you more resistant to insulin. And strenuous activity, especially competitive sports, triggers increased stress hormones, in which case blood glucose usually increases (at least temporarily).

In general, we know that different exercises affect us differently. And we also know that we’re all very unique, and the same exercise affects different people differently. Our blood sugar response will also depend on our level of physical fitness and personal exertion. Generally speaking, 30-40 minutes of running brings different results than an hour of cycling, swimming or even boxing. The intensity of the activity is often as important as the duration.

Finally, even though it can be unsettling, we must be persistent! A high blood sugar is annoying, especially after exercise. Nevertheless, exercise and activity are very good weapons against your diabetes monster and they work in your favor in the medium to long term, even if you’re struggling against those BG boosting stress hormones in the short term.

Generally, the post-exercise blood sugar spike settles down and returns to normal after an hour or two, so check again after some time if you’re able to. And the exercise itself pays dividends for much longer than that, so the tradeoff is well worth it. However, if you notice that things aren’t moving in a good direction I recommend making an appointment with your diabetes care team to talk about it. There are many options available, and they’ll help find something that works well for you.

Good info, Markus! Thanks!


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  • amy

    that article was not very helpful. I am type 1 and try to be in ketosis most of the day. I do high intensity interval training everyday for about 40-60 minutes. I found that if I exercise in a fasting state my blood sugar goes up afterwards. However if I eat 5-6 hours before exercising then my blood sugars are fine. I believe this has to do with restoring glycogen to the muscles. Fat takes longer to breakdown into energy than sugar. so when I eat before I have readily available glucose in my muscles, and the liver does not need to respond by raising blood sugars until my body can supply the rest of the energy needed through fat/ketosis. This is just my theory … but I have done a lot or research on it. If I DO end up working out without eating first (i usually try to have a few blueberries or something 2-3 hours before in worst case) … then I take a couple units of fast acting insulin (humalog will take about 10 minutes to work) right before the work out. This has proven, for me at least, to reduce my afterwork out highs by about half.

  • Thanks for the feedback, Amy, and for sharing so much of your experience. Very interesting!

  • Bobby McDaniel Jr.

    Amy, just to be clear; in order to maintain good blood sugar during exercise I should eat several hours before ? I have high blood sugars when working out. Also, what should this meal consist of ? Carbs/fats/etc

  • Tuki

    Dear Readers,

    I find this article interesting and true, to keep my blood sugar spike in the morning at a minimum I go to the gym right after I wake up. This helps stabilize my sugar lever and keep it under 100 mg/dl. You have to understand your body needs more sugar when you work out (I am eating also a high fat low carb diet) and if you do not have enough sugar in your blood and still have some stored the body will release it and you will have more then your insulin level can handle then you will have a higher blood sugar when your workout ends. What I can recommend if you are not in ketosis, that you eat something before you go to the gym so your body wont release any glycogen stored, if you are living the keto lifestyle then your body should be fine with the ketones that you have and it should not produce any excess sugar. Take in consideration that every Type 1 is different. For ex. I still have days where I do not use any insuline and I still keep my blood sugars in the 80-90mg/dl range, but there are days where I need both types of insulin to keep my levels in control. Anyhow exercise is a must and a good investment in the long run even if it rises your blood sugar levels.

  • Araoli Murugayyan

    Dear Readers,

    My sugar level goes up after jogging. (45 min jogging)

    What should I do?

    Can I neglect that sugar reading after exercise?
    Can I stop jogging or reduced duration?
    Shall I eat something (carbo / sweet) before jogging?

    Please suggest friends.


    I’ve adopted an “intermittent fasting” protocol to address my T2D and my weight. So far, I’ve lost 45 lbs., and my fasting BG is about 105. But after I exercise, in my case, playing 2 hours of intense racquetball and some weight lifting, my BG spikes to 240+. After about an hour post-exercise, my numbers plummet to 90-ish. From what I’ve learned, since my last meal was, nearly, 24-hours ago, the glucagon has been converting body fat to glucose to feed my muscles, and during the hour AFTER exercise, that sugar gets converted to energy and for muscle regeneration.

    Finally, most doctors get their patients to “chase the numbers.” I believe it is much more important to understand WHY we have higher glucose numbers than to take something to make those numbers go down. Transient spikes in BG should not be that much cause for concern if the overall trend is getting the A1c to a normal range.

  • Excellent point!


    Thanks for your reply, Scott. I was diagnosed a T2D in 2003, when my A1c rose to 6.8, I was just 40 years old then. Since that point, I’ve been learning about how and why I got to where I am, and for my condition, the simple truth is I became insensitive to my body’s production of insulin. Thus, the only protocol for me was to reset my body’s insulin sensitivity, which I did through fasting.

    How did I arrive at this protocol?

    I kept reading stories of obese individuals who received bariatric surgeries, the actual type was irrelevant it seems, who after a few days, no longer needed their T2D medication–it appeared that they were cured. Time and time again, stories were told about how Mr. or Ms. X no longer needed any medication after their bariatric surgery.

    So then, the question for me was: Can I get that same result WITHOUT the surgery?

    The answer is yes, but it isn’t as easy you’d think. It takes a bit of time and a lot of willpower. For most, I’d say a couple of weeks of eating high-fat, low-carb, and no more than 400 calories per day for a total “reset.” Then after that, eating a modified Paleo/Atkins will continue to maintain your hard-earned gains. So far, I’ve kept my weight off for 2-years, and I still don’t need Metformin, or any other blood-sugar reducing medication.

    Finally, I keep reading about those who panic over the liver-dump of glucose during strenuous exercise as something to battle. Once educated, those whose blood sugar rise to levels that most medical practitioners would consider “unhealthy” should understand that the high blood sugar level indicates that our body is getting rid of the excess sugar that created our condition in the first place–too much sugar in our diet that ended up on our gut or backside.

    Therefore, trying to stop this from happening is like putting a “STOP” sign to weight loss, when in its place, we should be ensuring that we are hydrated enough with a bit of salt and potassium to replace what our body is getting rid of: Excess sugar.

    Be well

  • Fascinating stuff, I really appreciate you sharing! That reset sounds so important. I’ve read a lot of stuff over the past couple of years about our bodies fighting so hard to stay at that higher caloric level that they get accustomed to (stupid caveman genes! 🙂 )

  • Thermal deal

    you cannot cure yourself from Diabetes like you can with gastric bypass surgery. The reason you do not have to take metformin at this time is because you have your diabetic symptoms under control through diet and exercise. You still have diabetes and will relapse into dangerous symptoms if you come of your diet and exercise routine.

    When a patient gets gastric bypass surgery they are actually curing their diabetes disease. This is because after gastric bypass the small intestine starts producing Glut-1. Glut-1 is a molecule that helps control glucose in the body.

    But great job controlling your diabetes. You should have a long and healthy life the way you are taking on your disease.

  • Thermal deal

    start off by jogging less. Read your blood sugar levels at different intervals and slowly build up until your body adjusts your to your exercise levels.

    lower impact or less duration until your body adjust is always recommended. You do not want to spike your sugar up to levels where you are causing harm to your body.

  • Thermal deal

    depends if you are type 1 or type 2 . Both disease have similar names but are completely different diseases.


    Thank you! But wouldn’t the same physiology occur with serious fasting similar to the effect of “gastric bypass” that would result in diabetes reversal? Why would bypass surgery “cure” diabetes, but serious fasting not? All I know is it works for me, and has for the past year and a half.

    Thanks again,


  • Kathy Braun

    I too am experiencing high sugars after an intense work out on the elliptical. Should I eat before or not is the question. Thanks to all who can help.

  • Alex Soury

    You are controlling your T2D with diet and exercise. In order to cure it you need to regain your insulin sensitivity and your Paleo/Atkins diet is no helping, in fact its the cause.

    Fat, especially animal fat and saturated fat impair insulin from doing it’s job thus requiring more and more. Saturated fat can also kill the insulin producing beta cell of the pancreas.

    Switching to a low-fat whole-food plant based diet will restore your insulin sensitivity.


    Alex, the medical community disagrees with you. I know you believe what you say, in other words, you are genuine in what you believe, if you were to seek information outside your realm of sources, you might see something different.

    For example: Yale Medical School tried to debunk Atkins, and it failed miserably. In fact, JAMA and its British equivalent, both recognize that no insulin is needed to break down fat, so no insulin is produced, which is where T2D comes from–it is called “insulin resistant” diabetes is it not?

    Finally, no credible medical study exists for your “fat impairs insulin from doing its job” claim. If this is what you’ve been taught, I implore you to reconsider the source. Atkins, Fung, and Yale Medical School have found that a high fat diet, low in carbs, especially from simple sugars like potato, carrot, corn, rice, and wheat, and all grains for that matter turn into, promotes less internal inflammation, a reduction to blood sugar, and an increase in better health. This is not my opinion, this comes from those who know, and have studied this fact.

    As always, be well.

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