Exercising with T1D: The Insulin-Food Balance Challenge

Three effective ways to avoid hypos and keep your blood sugars stable during cardio workouts, and the pros and cons of each

Staying active and consistently working out promotes heart health and weight loss and can have a profound impact on a person’s insulin resistance, which can help reduce prescription costs and make blood sugar management much more straightforward.

But exercise comes with its own difficulties. 

  • For many, it can cause drastic blood sugar fluctuations that have to be managed. 
  • For others, exercise increases appetite and leads to consuming all the extra calories you just burned, which can make weight loss and the associated benefits impossible to achieve.

How do you exercise without setting in motion a blood sugar rollercoaster or an endless eat-to-burn cycle that gets you nowhere depends on the individual.

One quick note before we begin: When talking about exercise in this article, I am referring exclusively to aerobic exercises that are likely to bring DOWN blood sugars. Anaerobic exercises, like weight lifting, actually tend to increase blood sugars and require their own special approach.

Managing Your Blood Sugar During Exercise

Exercising with diabetes is possible. 

In fact, excelling at physical activity with T1D is possible. We know this from seeing the many type 1 athletes who have made that very task into a career. 

Even professional athletes, however, have not found one right way to work out. 

Here are three options that will help you find success with exercise. 

1 — Reduce Mealtime Insulin Prior to Activity

One approach many people find helpful for avoiding the lows exercise can induce, is to cut down on the amount of insulin they take during the meal just before exercise begins. 

Depending on the intensity of exercise you plan to do and the size and makeup of your meal, that may mean cutting your meal bolus in half, skipping it altogether, or just taking a couple of units off.

This approach can work well if you tend to exercise at the same time each day and eat consistent meals. But even then, it will likely take some experimenting to figure out exactly how much to reduce your bolus to avoid going too low or too high during your workout.

One thing to avoid when using this method is that your blood sugar can go up so high before you begin exercising, that you risk shedding ketones during your workout.


  • Doesn’t require adding extra calories to your diet
  • Saves on insulin
  • Can be done by those using MDIs and those on pumps


  • Requires a consistent schedule
  • Requires working out soon after eating a meal
  • Can result in ketones if insulin is too restricted

2 — Eat Carbs Before Exercising

One approach that requires considerably less planning than reducing boluses is to simply eat something right before you exercise.

Of the three methods listed here, this one is the most effective according to scientific research.

  • One study that compared bolus dose reduction and carbohydrate supplementation during workouts found that eating carbs before working out was more effective in preventing hypoglycemia than simply cutting the prior meal’s bolus. 
  • Another study found that drinking 20g of fructose over the course of a one-hour workout was effective in preventing hypos in 93% of the subjects.

Of course, what to eat and how much will depend on the type and duration of the exercise you are doing. 

Eating or drinking a smaller amount of simple carbs before a short workout typically works well, while longer sustained workouts may require continuously drinking something with some sugar. If constantly taking in carbs while exercising doesn’t sound appealing to you, eating a more complex snack that includes carbs and protein can help keep sugars stable over a longer period of time.


  • Works well for unplanned exercises
  • Can be easily adjusted based on the length and intensity of the workout
  • Can be done by those using MDIs and those on pumps


  • Requires eating extra calories
  • Means working out with something in your stomach
  • Easy to overdo and end up with a high

3 — Lower Your Basal Insulin Rate

If you don’t like the idea of working out after a meal and would rather not add extra calories to your diet, then lowering your basal rate may be your best option to avoid lows during exercise.

Unfortunately, unless you are planning an all-day activity like climbing a mountain or running a marathon, lowering your basal rate only works if you use an insulin pump.

To successfully use a reduced temporary basal rate during exercise you have to time everything right and experiment with the percentage to see what works for you.

Since pump insulin typically takes at least an hour to peak, you will have to start your temporary lower basal well before you actually start working out. Ideally, you want your blood sugar to start to rise at about the same time you’re set to start your workout. 

Depending on the intensity of the exercise, you may want your temporary lower basal to expire just before your workout is over or, if you expect to experience a post-exercise crash, not until after you are done working out.

In terms of how much to lower your basal rate, that will depend on how intense the exercise will be. A good rule of thumb is to start at about 75% for mild workouts and lower it as the intensity increases. Just make sure you do have at least some insulin moving into your system — even for really strenuous exercise — or your body could start shedding ketones at too high a rate.


  • Doesn’t require extra calories
  • Allows you to work out on an empty stomach
  • Can be easily adjusted for intensity and duration


  • Only works for pumpers
  • Requires planning ahead
  • Will take some experimentation to get right

Consider Your Exercise Goals

In the end, which of these methods works best for you will depend largely on your personal preferences and your exercise goals.

  • If your main reason for exercising is to lose weight, then obviously consuming extra carbs before your workout is going to slow the process down. 
    • In this case, cutting mealtime boluses or reducing your basal rate will be a better choice.
  • If you are exercising simply for the health and strengthening benefits, then a little extra sugar or a protein shake isn’t going to hurt. 
    • You still need to consider if you are the type of person who sticks to a strict schedule and can use set mealtimes and exercise times to their advantage, or if you need the flexibility to be able to jump into action as soon as the opportunity presents itself.

It is a good idea to experiment with each of these techniques (maybe even try combining a couple) to see what works best for you and your body.

If you are new to exercising with diabetes, here are some more tips to help you find success.

Expert Reader Opinion

Karen wrote to us after this article was published and we thought her comments were helpful and important.

‘I do the opposite of what is recommended for taking insulin and exercising. I used to go low when playing 4 hours of golf or walking and running.

Now I follow a very low carbohydrate diet. I follow the diet of Richard Bernstein. He’s a well-known endocrinologist. He is now 87 years old and has been diabetic since he was 12 years old and has no diseases whatsoever. He has been a lifesaver.

On the days I am going to exercise I eat proteins only…. an egg, bacon or piece of cheese. I take no insulin. During a day of golfing my blood sugar remains 90-125 on average. If I take any insulin the exercise plus the insulin will gradually drive my blood sugars down.

I think this approach works because of my low carb diet. My daughter and grandson are also type 1s. They eat a lot of carbohydrates each day so their morning blood sugars might be higher and this might not work.’

I always carry glucose with me. I sometimes eat fruit when I play golf. No problems with the sugar from the fruit while exercising. But I don’t always do this’

Sara Seitz is a freelance writer specializing in blog, article, and content writing. She has had type 1 diabetes for ten years but has never let it stop her from living the life she wants. Lately, she has been busy figuring out how to manage her diabetes while raising a spirited toddler. Sara enjoys traveling, hiking and experimenting with food as a means to better health. She lives in Fort Collins, Colorado with her husband, daughter and their pack of various pets.

Related Articles

Back to top button