Proper nutrition is key to a successful run, race, or workout. But for runners with diabetes, fueling (and the timing of your fueling) is even more important. And, often, medication plays a role as well.
Pro Tips for Fueling Your First Marathon Amanda Kirpitch, MA, RD, certified diabetes educator (CDE), to break down everything runners with diabetes need to know to keep running strong.
Keep in mind, every person is different, so it’s important to speak to your healthcare professional before making any dietary or exercise changes.
The basics of diabetes
There are two kinds of diabetes diagnoses—type 1 and type 2. Type 1 diabetes is a lifelong condition in which the body produces little to no insulin, which is the hormone needed to allow sugar to enter the body’s cell from the bloodstream. Type 2 diabetes is a condition in which the body can’t effectively use sugar as fuel, creating too much sugar in the bloodstream.
The most common symptoms of diabetes are increased thirst, urination, hunger, exhaustion, and weight loss. If you are experiencing any of these symptoms without cause, you should contact your doctor.
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How does running affect your blood sugar?
Whether you have type 1 or type 2, you should monitor your glucose levels closely during your run, Kirpitch says, because your glucose levels may fall during and after your run. It can fall as quickly as 30 minutes into the activity and anytime thereafter. (Also, exercise can exacerbate an already-falling glucose level, highlighting the importance of monitoring your sugar before activity.) The risk for hypoglycemia remains immediately following activity and up to 24 to 48 hours after.
However, the body’s response to activity may differ depending on the medication a person may be taking to manage their diabetes. If a runner is taking a hypoglycemic oral medication or insulin, the risk for hypoglycemia (low blood sugar) is higher. If a runner with type 2 diabetes is not taking insulin or hypoglycemic agents, the run may require less monitoring.
When using insulin to manage diabetes, keep in mind that if there is insulin in the body from a previous meal still working to reduce glucose (commonly referred to as insulin on board or active insulin), the risk for hypoglycemia is higher and adjustments should be made, says Kirpitch.
“A recent insulin dose can be more powerful if it is quickly absorbed into a working muscle,” Kirpitch says. “Many runners choose to inject insulin into their abdomen, and avoid dosing in legs and arms, which are muscles most engaged during running.”
There is also a risk of hyperglycemia (high blood sugar), particularly if diabetics may reduce the amount of insulin they receive during a run, or if they don’t think about the impact of anaerobic activity, says Kirpitch. High blood sugar can cause the body to produce ketones (molecules produced by the liver), which can also be quite serious.
How often should a runner check their blood sugar?
Checking glucose throughout the day (via CGM or fingersticks) can help to better understand glucose patterns and adjust medications accordingly. Eating a variety of foods helps to better understand glucose response and better dose for the meals/snacks you’ll need to fuel your workouts and your day.
“Working with your diabetes team to learn the response to running at different times of day and planning nutrition and medications to optimize performance and glucose management is key,” Kirpitch says.
If you’re not wearing a CGM, it is good practice to check glucose at 30-minute intervals during exercise to assess patterns and make adjustments to management routine, Kirpitch says. It is best to catch a dropping glucose level before it goes low, so you can appropriately treat and continue activity. Once glucose is low, activity should stop until glucose returns to normal.
Keep in mind CGMs use interstitial fluid to monitor glucose, and there is a delay from blood glucose. Due to rapidly changing glucose during activity, it is good to recognize that glucose may be lower than value displayed on CGM.
How to recognize and fix fluctuating blood sugar levels
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- Shaky
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- Hungry
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- Tired
It’s important to keep in mind that with adrenaline and focus that often comes with exercise, especially on race day, classic symptoms of hypoglycemia can be masked. This is why it’s critical to spot check glucose frequently throughout activity or utilize a CGM to assess patterns, Kirpitch says.
How to fuel pre-run
Generally, the fueling for runs will be similar to what would be recommended for those without diabetes. “Ideally the medications and/or insulin would be dosed according to the fuel needed and subsequent glucose response,” says Kirpitch.
Experts recommend that your glucose levels pre-workout should be about 126-180 mg/dL.
- If blood glucose is below that range, consume 10–20 grams of a fast-acting carbohydrate to bring it up (and more carbohydrates, if there is active insulin from a previous bolus.)
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- For runs that are longer than 60 minutes, recommended carb intakes range from 1-4 g/kg body weight 1 to 4 hours before the run.
Choose snacks that are quick-digesting carbohydrates and have small amounts of protein and fat closer to the time you run in order to minimize gastrointestinal stress. Have more substantial meals including fat, protein, and higher-fiber carbohydrates 3 to 4 hours pre-run.
What to carry when you’re running
If you’re running for less than an hour, you don’t need to worry about bringing fuel for that run; pre-run snacks and meals are usually sufficient.
However, runners at risk for low blood glucose should carry a form of quick-acting glucose to treat potential low blood glucose or hypoglycemia. Typical treatments are glucose tabs, glucose gels, dried fruit, candy, or sports drinks, suggests Kirpitch. Runners at risk for low blood glucose should also carry a meter or wear a continuous glucose monitor (CGM) to monitor glucose during activity.
Runs that last longer than one hour can be aided by fueling with mostly carbohydrates every 30 minutes to one hour. Fueling can begin 30 minutes into the run at 30 to 60 grams per hour for runs lasting one to two hours and 60-90 grams per hour if runs are longer than two hours.
“I always recommend runners carrying their own fuel and treatment as opposed to relying on fueling stations to have what they want or need at the right time,” Kirpitch says.
Set up for race day success
There are many factors that go into managing your diabetes on race day. Running is considered an aerobic activity, which often results in a drop in glucose. However, your surge of adrenaline before the race starts (and at any other points in the race) can cause a rise in glucose, Kirptich says.
So, you should learn how your body reacts during different exercise intensities and lengths before race day so you know what to expect.
“It’s important to consider the different ways your body responds to glucose throughout a run as well as different types of runs,” Kirpitch says. “Practicing with some shorter race events can give you an idea of how your body responds to the stress of a competition prior to your big day.”
After the activity, refuel with carbs and some protein. There is a risk for hypoglycemia immediately following activity and up to 24 hours later. There is also an increased risk for hypoglycemia overnight particularly following a late afternoon or evening workout. It’s a good idea to ensure adequate carbohydrates at these pre-run meals and snacks.
Is it possible to regulate blood sugar through exercise?
Activity passively allows glucose into the cells, reducing the body’s need for insulin. This allows for increased insulin sensitivity—which in turn can make glucose levels lower. Often, activity (as part of a healthy lifestyle) can improve glucose regulation, Kirpitch says. However, self-management strategies around exercise and activity are highly individualized.
