• Ariel Warren, RD, CDE, CPT, T1D

How to Exercise with Type 1 Diabetes without Low Blood Sugar

Losing weight feels like an uphill battle. Throw Type 1 Diabetes in the mix and all bets are off! You now feel you are taking on the impossible.

Cut out the junk and eat more veggies?


Add in some exercise?

"Ugh, fine, it's doable."

Now, don't get low and therefore have to gorge on glucose tabs or juice because of the change in eating and additional exercise?

"Yeah. No way."

As a Dietitian, a CDE, but most importantly, a T1D (where I get my street cred), I understand where you are coming from.

There's nothing like working hard at eating the "right foods" (we'll get into what that entails), and busting your butt at the gym, but then...*GASP*, you look down at your CGM and you see the dreaded double arrows pointing down. And you are now feeling the shakes.

Two minutes later, you are sitting (not running) on a treadmill, snarfing down glucose tabs (if you're lucky) or any other edible food that has carbohydrates found at the bottom of your gym bag.

And of course, now you feel like a crazy person for not only, not working out while you are at the gym, but stuffing your face. And not with some health food, you are stuffing your face with candy. Probably no one is staring, but your insecurities get the best of you and you feel like EVERYONE is watching.

You then cut out early and feel a bit defeated because the 200 calories you burned while getting in the 2 mile run. Well, you just ate that in glucose tabs.

My friend, if you have been in this situation, you are not alone. As a T1D myself, I feel it is one of the learning strips of having T1D. I remember an incident that happened to me awhile ago when I didn't know better and didn't have the tools I have today. I was at the gym after eating a high carb dinner, so my insulin levels were high and then I did a cardio session.

High insulin + cardio = low blood sugar.

So there I was, on the sidelines, gobbling down rolls of smarties. I think glucose tabs are the best, but smarties are less expensive and they taste less like chalk.

The purpose of this post is to teach you how and when to exercise so you are not the "smarties gobbler" at the gym.

Through the many years of being a T1D, I have come to find, through trial and error, hours of research, and working with many T1D patients what works, and what doesn't.

Below are my secrets.

1. Workout Fasted.

Working out fasted allows for two great things.

#1 When you workout fasted, your insulin levels relating to food are low. The lower your insulin before a workout, the less you have to worry about your blood sugar nose-diving mid-workout and thus having to quit and take a glucose tab break. However, if you are doing a HIIT or intense workout, you may actually need a bit of correction before the workout. I'll explain this further on.

#2 When food is low (glucose), insulin levels are low. If you have a broken pancreas, we have to make up for this missing link by bolusing and taking a shot for the carbs (glucose) in our food. Your body's primary source of energy is glucose. Glucose is moved from the blood into the cells by insulin, inside the cells the glucose is used for energy. When glucose (food) is limited, insulin levels are low, and then your body will have to use something to use as energy for working out. Depending on how long you have been fasting before your fasted workout determines how much glycogen (stored glucose) is available for your body to use. If glucose AND glycogen stores are low, your body will have to use fat for energy. Which then allows your workout to literally become a fat-burning session. Add High Intensity Interval Training (HIIT) or anaerobic exercise and the fat-burning is only intensified. When done right, doing a fasted workout can be a beautiful thing for your diabetes and weight loss.

NOTE: If you are starving and you feel like you just can't muster up the energy to do a fasted-workout, don't beat yourself up, it takes time to be able to do fasted workouts. What you can do to get most of the benefits is to eat something low in carb, moderate-to-low in protein [because certain building blocks (AKA amino acids) can turn into carbs and raise insulin demands], and high in fat. My go-to when I have to eat something before a workout is a handful of nuts or seeds.

2. Know How Exercise Affects Blood Sugar.

Depending on the type and intensity of your workout determines how much glucose is used and how much is produced. There are three main different types of workouts.

#1 Aerobic or Cardio

A workout that allows you to breathe.

Aerobic means [free oxygen] AKA = breathing

Examples: brisk walking, steady-state jogging, swimming, dancing, skiing, biking.

This type of exercise tends to burn through glucose and also causes insulin to become more effective during the workout. These 2 factors together cause your blood sugar to drop, drop, drop! Especially about 15 minutes into the workout. This type of workout may reduce insulin resistance hours afterwards, but not nearly to the extent as anaerobic or mixed workouts. The best way to reduce insulin resistance is to work muscle, and cardio is more about burning calories in the moment, and not as much about working, tearing, and building muscle.

#2 Anaerobic or High Intensity

A workout that doesn't allow breathing.

Anaerobic means [an = non] aerobic [free = oxygen] AKA = no breathing

Examples: Resistance training, sprinting, jumping.

This type of workout tends to release hormones (think fight or flight) that actually cause your insulin to be less effective initially, and also causes your body to release glucose from your skeletal muscle and liver. This process is known as glycogenolysis (the breakdown of glycogen). Glycogen is simple stored glucose, so when glycogen is broken down ibto glucose, blood sugar (glucose) increases.

High blood glucose and hormones that cause you to be more resistant to insulin can cause your blood sugar to spike at first, but then later causes your body to become insulin sensitive for many hours afterwards. As crazy as it sounds, you may actually need to give insulin before doing this type of workout because of the insulin resistance and glucose production. HOWEVER - make sure to be cautious with giving insulin before working out.

How do I safely determine how much insulin I need before a HIIT or anaerobic workout?

1. Perform a HIIT workout a couple of times without pre-dosing to see where your blood sugar usually spikes to.

2. Give 1/2 a correction BEFORE the workout to see how it affects your during and post exercise blood sugar. Keep glucose on hand in case of a low.

3. Adjust, and adjust again. See if you need to add more or less to the pre-workout dose. Keep glucose on hand.

NOTE: The larger the muscle that is exercised, the greater the blood sugar spike. For instance, you will likely see more glucose production (blood sugar spike) when doing a leg weight lifting session compared to arm weight lifting session.

#3 Mixed Aerobic and Anaerobic

A workout that allows breathing mixed with non-breathing.

Example: Jogging mixed with an interval of push ups and jump squats, then more jogging.

This type of workout tends to be more blood sugar neutral. However, the higher the intensity, the higher chance it will cause a similar response as to an anaerobic workout. Sometimes a mixed workout can cause an even greater blood sugar spike if your cardio parts are actually in the form of cardio anaerobic bursts like sprinting. This type of workout will reduce insulin resistance for many hours after the workout as well.

3. Use your Fasting Blood Sugar to Determine Your Workout.

Now this is the fun part. You can use your morning, fasted blood sugar to determine what type of workout to do.

Below are three different examples of how to workout if your fasted blood sugar is...

  • High: > 130 mg/dL

  • In the Zone: 80 - 130mg/dL

  • Low: < 80 mg/dL

#1 High = > 130 mg/dL

I understand for many, the thought of considering 140 mg/dL as high may make you roll your eyes. However, to please the masses, we will say high is above 130 mg/dL while fasting.

For example, if you are running "high" (above > 130 mg/dL), I would take at least 1/2 your correction dose, then do a steady-state cardio workout so your body can use the insulin and burn through the available glucose to lower blood sugar.

NOTE: Again (as mentioned previously), if you haven't done a correction before a workout, do so gently and as long as you have glucose or juice on hand.

With any fasted cardio, you will likely spike at first even with aerobic, steady-state cardio, but then your body will use the insulin, and burn through the glucose and come down. Expect at least 15-20 minutes before you see this blood sugar lowering magic begin to work.

If you are using a closed-loop system via pump, you will likely already have higher IOB levels than usual, therefore your pump will not let you correct. Do not override this, the correction dose has already been taken care of for you. Just stick with cardio and watch your blood sugar come down.

What if I am high? Can I still workout?

There is a limit. If you are high before a workout, check for ketones! Especially if you are using a pump and if you are above 250 mg/dL (to play it safe).

If you have moderate (or greater) ketones, take a shot (even if you use a pump), drink plenty of water, and wait it out. If you are vomiting, call your doctor or urgent care ASAP. However, if you just have mild ketones, still take your normal correction insulin dose and drink water, but you can do a mild steady state workout (such as walking) to bring down your blood sugar. Check during your workout if you have mild ketones. If your mild workout is causing your mild ketones to increase, STOP your workout.

What If I my blood sugar is high, but I am using an insulin pump?

If you are high and using a pump that doesn't use a closed-loop system, I would take a shot with a syringe rather than use your pump since the high could be from a blockage or a bad infusion site. If you are using a closed-loop system, take a shot via syringe, disconnect from your pump, but bolus the amount that you took with the syringe. That way your Insulin on board (IOB) is still accurate and it doesn't cause your pump to over basalize you because of your current high blood sugar. Next, change your infusion set and possibly the insulin as well, and then keep your pump on you throughout the workout. If you are starting to nose-dive, you can use a decreased temp rate.

#2 Golden Zone = 80 - 130 mg/dL

Let's say you are in the fasted golden zone. If you are crazy (like me) and really like tight control, you can do a 1/2 correction on the higher end (closer to 130 mg/dL), and then start with aerobic, but then finish out with your workout of choice. Meaning either more aerobic such as jogging or bust out an anaerobic workout such as HIIT.

#3 Low = < 80 mg/dL

You should NOT workout if you are this low. But if you are crazy (like me again), and you have glucose tabs or smarties on hand in case something does go array, you can start with sprints to crank your blood sugar up, then finish with whatever type of workout that pleases you. I do not advice this, but many times I have performed sprints when my blood sugar was sitting in the 70s, so I cranked out HIIT spirints to shoot my blood sugar up by about 30-40 points. I would then finish with more HIIT or if I'm feeling lazy (which is more often than I'd like to admit), I will finish with watching some garbage show on Netflix and do a brisk walk/run for 2 more miles.

Anaerobic activity is your secret weapon for decreasing low blood sugar during your workout. For instance, if you are on a run, and your CGM (or glucometer) shows that your blood sugar is started to trail down, add intensity! Research has shown that by adding intense spurts can increase glucose production by the liver and skeletal muscle and therefore decrease a low. However, you need to be careful. Always keep glucose (or smarties) on hand.

4. Monitor. Monitor. Monitor!

If you are new to working out, watch your blood sugar closely. An anaerobic workout can cause more low blood sugar episodes after hours of the workout because your body is replenishing muscles from the workout that has more intensely used up glycogen stores. Because of this, your glucose is being used and your blood sugar is dropping more than usual. This is great for reducing insulin resistance and helping with weight loss, but can cause for more lows, and more glucose tabs or smarties parties.

And for the 12-24 hours after your workout, keep monitoring. After that amazing workout (great job, by the way). You will likely need to reduce insulin so you don't get lows.

On a pump: You can start with a 10-30% reduction for the next 6-12 hours. Understand that you may need a reduction in basal for up to 24 hours, but start with 6-12 hours. Also, watch extra closely before bed and make sure you have a low alert if using a CGM as you sleep or get up once during the night to check (especially if you don't feel lows).

Use MDI: You can reduce insulin at mealtime and/or reduce your split dose of your long acting insulin (such as Detemir, Basaglar, or Lantus). If you are using Tresiba or Toujeo (which are ultra-long lasting insulins) and don't split your dose, then it is better to decrease a mealtime dose or increase your insulin to carb ratio (ICR) for the meal following your workout.

If this is confusing, do not change your routine if you unfamiliar with these terms or confused. You do not want to mess with insulin.


Final note. If you need help with working out, losing weight, adjusting insulin settings, or you feel it would just be nice to have someone who understands diabetes to cheer you on and tell you how amazing you are? Send me a message so we can work together. I understand I am an odd duck who apparently can't get enough of diabetes, but I absolutely love working with people just like you.

Even if your blood sugar is somewhat decent, you have to acknowledge how livable your current routine is. Maybe you are eating low carb, but feel your blood sugar goes absolutely bananas when you even look at a piece of bread. Perhaps your blood sugar loves to take you on a daily roller-coaster ride and it's getting really old? Maybe you want to lose weight, but you don't know how, or when, or what to do for food and exercise?

My friend, I'm here to help. As a Registered Dietitian Nutritionist, a Certified Diabetes Educator, a Certified Pump Trainer, and a T1D (for street cred), I have the credentials, schooling, education, and experience to help you get your life back. If you need help with your diabetes, write me a message so we can work together. I work with people with T1D through online video calls all across the United States through my online telehealth private practice. Working with people to reach their diabetes, weight, and fitness goals is what I love to do. I also work as a CDE and a RD at an Endo clinic where I get to work with people with diabetes in-person. If you are burned out, or just plain sick of diabetes, send me an email. Tell me what's going on and ask me any diabetes-related question. I am on your side and I want to help you.


Ariel Warren, RD, CDE, CPT, T1D

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