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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.

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