Exercising with type 1 or type 2 diabetes when you’re taking insulin, or any diabetes medication, is not easy. In fact, it’s quite complicated. But I want to state for the record: you are absolutely, 100% capable of figuring out the complicated details so that you can feel more confident and in control of what happens to your blood sugar while exercising. Whether you’re headed to the gym, to a mountain for a 4-hour hike, or to your garage for some jump-roping, once you figure out the tiny details, you’ll be able to get in your workout, no problem.
As people with diabetes, a massive part of living a healthy life means trying to keep our blood glucose levels in our goal range — even while exercising. Meaning, exercising with a blood sugar of 250 mg/dL just to prevent yourself from dropping low during your workout is not OK. Likewise, exercising with a blood glucose level of 50 mg/dL isn’t healthy either. The difference? Most of us can feel that 50 mg/dL when we exercise — we’re physically unable to exercise at all because that level is simply too low for strenuous movement. On the other hand, a 250 mg/dL blood sugar is, for some, a level that doesn’t prevent physical activity. But just because you can still run, leg curl, or spin doesn’t mean it’s good for you.
So then, what’s a PWD to do? 🤷♂️ 🤷♀️ You can’t go too low, but you can’t be that high either. Are you just supposed to not work out? No way! 👎 Ultimately, working out is one of the best things we can do to keep our blood glucose levels in range and insulin resistance low. But how to get there? How to make it worth it? ⬇️⬇️⬇️
Here are 5 tips for keeping your blood sugar in a safe, healthy range during exercise:
1. Know what type of exercise you’re doing: aerobic vs. anaerobic.
Understanding the difference here is perhaps the most important detail. If you eat a banana without insulin to cover the carbs right before your workout, but end up doing an hour of weights instead of an hour on the treadmill, you’re going to find your blood sugar well above 300 mg/dL by the end of your workout. Anaerobic exercise relies on energy stored in your muscles (a process known as glycolysis), as well as body fat for fuel. Conversely, aerobic exercise (also known as “cardiovascular” or “cardio”) will generally burn glucose for fuel, lowering your blood sugar. Anaerobic exercise, on the other hand, relies on energy stored in your muscles (a process known as glycolysis), as well as body fat for fuel.
Translated to mean “without oxygen,” anaerobic exercise simply can’t burn glucose for fuel because your heart-rate is so high during those short bursts of intensity. Instead, glucose stored in your muscles (known as glycogen) is cycled through the process of glycolysis for fuel. The added bonus is that during the rest periods between those bursts of intensity, your heart rate comes down and your body can burn fat for fuel, too. This means that if you’re going to do an anaerobic workout (like weightlifting, high-intensity intervals of spinning or sprinting combined with intervals of lower intensity, CrossFit, etc.), you can generally expect to see your blood sugar either remain stable or actually rise a little. Or a lot! For example, I know that an intense weightlifting workout will raise my blood sugar sometimes up to 100 points. I also know that short-bursts of sprinting combined with several minutes of slow walking will cause little to no rise in my blood sugar.
After anaerobic exercise, you can expect that your next snack or meal will need a lot less insulin because your muscles will want to refill those glycogen stores with glucose, easily burning up more of your meal. How much you can reduce your post-workout meal bolus is going to vary from person to person and based on what type of exercise you did. Caution, trial and error is your friend here!
Aerobic exercise, on the other hand, generally means your heart-rate is elevated for a prolonged period of time. Your body actually can’t cycle enough oxygen to your fat cells to use for fuel. Instead, your body relies primarily on glucose for fuel. This means that if you head up a small mountain for an afternoon hike, you can expect to be burning glucose constantly. The same goes for a power-walk: your pace is consistent and, thus, your heart-rate is elevated. When you’re hiking back down that mountain, however, your heart-rate will be remarkably lower and your body won’t need those extra carbs (or reduced basal rate) that they needed on the way up.
You see, it’s really all about your heart-rate! What it’s doing, when, and for how long. Even a medium-intensity yoga class can raise your heart-rate consistently and lower your blood sugar.
After aerobic exercise, you will likely be more sensitive to insulin and need a slight-to-moderate reduction in your basal rate or bolus for your next meal. How much you can reduce your post-workout meal bolus is going to vary from person to person and based on what type of exercise you did, and for how long. Caution, trial and error is your friend here!
2. If you exercise in the morning, try doing your workout before eating breakfast.
You can thank Schwarzenegger and Franco Columbu for this one. Bodybuilders have known about the benefits of fasted exercise for decades. I didn’t believe it at first when my powerlifting coach explained this to me years ago. After a few experiments, however, I came to fully trust this magical time of day for exercising without worrying about my blood sugar.
Here’s how it works: when you perform any type of exercise on an empty stomach first thing in the morning, with an in-range blood sugar and accurate background insulin doses, your blood sugar will not drop. Instead, your body is going to burn body fat for fuel! If you are still in a truly fasted state (you haven’t eaten), then you haven’t taken a bolus of insulin for food either. The consumption of food, along with a bolus of insulin (even for people without diabetes) is what signals your body to start burning glucose for fuel when necessary, like during cardio exercise. By not eating breakfast, and, instead, heading straight to the gym or out for a long walk with your dogs, your body is going to burn body fat for fuel and your blood sugar will remain stable!
Here’s what it looks like in real life. I’ve been taking my dogs for an early morning, long walk at 6 a.m. I wake up and test my blood sugar to confirm I’m not low. If I’m high (over 200 mg/dL), I take no more than a ¼ unit of fast-acting insulin to help it start to come down with the help of exercise, chug a little water, and head out the door for a 40-minute fasted power-walk in the woods. I know I don’t have to worry about my blood sugar dropping too low because I haven’t eaten. Meaning, my body is still burning fat for fuel, and the correction dose I took for the high blood sugar was minimal. If my blood sugar is actually in perfect range when I wake up, even as low as 80 or 90 mg/dL, I would simply head out the door for the 40-minute walk in the woods because in a fasted state, I know for sure that my body is going to be burning body fat for fuel, not glucose.
In my real-life example above, I was doing aerobic exercise. But if you decide to do anaerobic exercise in the morning in a fasted state, you may see your blood sugar rise. This happens with more intense anaerobic exercises, like CrossFit or heavy weightlifting. The intensity of those workouts calls for more glucose (glycogen) to be released from your muscle stores. This is a normal, good thing! But it means you may find you need to actually give yourself a small dose of insulin before this type of fasted exercise.
Personally, this was my favorite time of day for weightlifting. I didn’t have the added variables of food and insulin on board. Instead, I knew I needed 1 unit of insulin before a fasted weightlifting workout, and I’d finish my workout effortlessly with a steady 100-ish mg/dL blood sugar level.
To determine if your anaerobic workout affects you in this way, do your first morning fasted exercise session without an extra bolus of insulin and simply see what happens! If your blood sugar rises, start out with a very small bolus before that workout next time and see what happens. Tweak your dosing as needed!
3. If you exercise in the afternoon or evening, try doing your workout when it’s been at least 3 to 4 hours since your last insulin bolus or meal.
This one is slightly more tricky. You’ve inevitably been eating during the day, but you want to keep blood sugar management as simple as possible so your evening workout isn’t sabotaged.
How it works: Much like fasted exercise in the morning, you’re creating that fasted environment in the afternoon or evening by ensuring that any large doses of fast or rapid-acting insulin are well out of your system. This guarantees that your body isn’t going to easily burn glucose for fuel during aerobic or anaerobic exercise.
As a full-time mom, the only time of day I could enjoy a hearty session with my beloved jump-rope was in the evening, around 7pm. To prepare my blood glucose levels for my 7pm workout, I made sure that my last meal was no later than 3pm. That way, there was no active rapid-acting insulin in my bloodstream by 7pm. If I did end up needing (or wanting) to eat during that 3-7pm window, I would choose something that is extremely low carb so that I either needed only the slightest amount or no insulin at all.
By giving my last insulin dose a 4-hour window to get out of my system before my 7pm workout, I could jump to my heart’s content, feeling confident that my levels wouldn’t drop even with a starting BG of 90 mg/dL.
Again, if you are doing an intense weightlifting or CrossFit-type of workout, you could see your blood sugar rise during fasted evening exercise. To determine if your workout affects you in this way, do your first evening fasted exercise session without an extra bolus of insulin and simply see what happens. If your blood sugar rises, start out with a very small bolus before that workout next time and see what happens.
4. Use very specific foods before, during, and after your workout.
The food you choose to fuel your body before exercising is critical. Eating a cupcake with buttercream frosting before your afternoon treadmill session is going to throw a giant, messy variable into your blood sugar management. Choose foods that won’t cause a terribly tedious blood glucose upset.
For example, lower carbs with a little bit of fat and/or protein. When I used to teach power yoga, I knew that one 6-ounce yogurt (with about 18-22 grams of carbs) eaten immediately before class started was perfect for keeping my blood sugar in my ideal range without dropping. If I ate it too soon before class, my blood sugar would spike, though. Then, I’d end up needing a tiny bolus of insulin to get it down so my blood sugar wasn’t sitting at 300 mg/dL during the entire class.
Even a spoonful of peanut butter is a great option for a simple boost. 🥄 If your favorite yoga class is somewhere between gentle and moderate, you may only need something that has the teeniest amount of carbs, plus a lot of fat. Peanut butter takes the win here!
The more protein or fat a food contains, the slower it will digest. Thus, the more slowly it will impact your blood sugar. If I’m going on a 4-hour hike and I know that 2.5 of those hours are uphill (meaning, my body will be working hard and requiring lots of glucose), I’ll eat ⅓ to ½ of a protein bar (my fave is the GFB bar) at the start of the hike. Then, I’ll eat the next portion halfway through going up. And finally, eat the last portion near the top, depending on my blood sugar at that point. All the while, keeping in mind that the trek down won’t burn nearly as much glucose, if any at all.
Choose wisely. Think about the macronutrients that make up the food you’re choosing. And be consistent!
5. Create different plans for different times of day and types of workouts. And take notes! 📝
Whether you exercise fasted in the morning, right after eating breakfast, or two hours after lunch, you’re going to need a different plan based on when you workout. The plan that works well after breakfast simply might not work that well if you’re exercising after dinner.
Whatever time of day, type of workout, and type of food/insulin preparation you do, take notes. Consider them when you change any of those variables. Once you’ve tested out your 6pm Yoga Class plan enough times, for example, you can always refer to that page in your notebook. That way, you know exactly what your body needs to ensure your blood sugar doesn’t sabotage your zen! 🧘♂️
The whole thing is one giant science experiment. Control the variables. Take good notes. Be patient. And have fun!
Don’t give up! You’ve got this.
You and I know both know that exercising with diabetes when you’re taking any kind of medication can be a complicated mess. On the flip side, exercise can do wonders for us. And there’s certainly no way I’m going to let diabetes keep me from doing the exercises I love! Even if my whole plan goes out the window and I can’t control all of the variables, and I end up having to eat 2 bananas to prevent a major LOW, that is totally OK. I tried. 💪
It might take a dozen “experiments” until you figure out exactly what helps you keep your blood sugar in a healthy, safe range during your favorite type of exercise. But that work is worth it! Ultimately, it means your body is moving, endorphins are flowing, and (believe it or not) your diabetes is benefitting.
Exercise is not a waste. Regardless of the highs or lows you may experience at first, the experimenting and persisting will be worth it in the end. Be safe. Be smart. Be patient. And have fun.