Test, then Flex: Managing Highs, Lows, and Ketones While Exercising

It doesn’t matter if you have type 1, type 2, or no diabetes at all—exercise is one of the best things you can do for your body and mind. And no, it doesn’t have to mean boring gym workouts!

 👉 Love scrolling YouTube, Instagram, TikTok? Try a dance or strength workout video.     
👉 Have a dog? Walking (or jogging) together totally counts.
👉 Into sports? From pick-up games with friends to playing on a team, it all adds up.
👉 Not into sports? Even joining a walking club or laps at the mall works.

Experts recommend aiming for 150 minutes of moderate activity per week—that’s about 20 minutes a day. But here’s the deal: you don’t need to start there. It’s way better to start slow, find things you enjoy, and build up your endurance. That’s how you’ll stay consistent and become stronger all around.

Mix it up: cardio (aerobic) helps in one way, strength (anaerobic) in another, especially when it comes to blood sugars.

Type of Exercise and Effect on Blood Sugar 

• Aerobic/Cardio (running, walking, biking, swimming) → blood sugar drops during activity 
  • 💡 Why? Your muscles are pulling glucose straight from your bloodstream for energy

• Anaerobic/Strength Training (sprinting, boxing, weightlifting) → blood sugar spikes during activity and then drops 
  • 💡 Why? Your body release stored glucose (glycogen) + adrenaline kicks in giving you a sugar boost

• Adrenaline rush during games or activity → high peaks with lows 

No matter the type, ALL exercise makes your body more sensitive to insulin (aka helps it work better). That effect can last up to 6 hours after you’re done—so keep an eye on your numbers, especially if you use external insulin.

Ketones? Go or No Go? 

Ketones are produced when the body is not able to use glucose for energy meaning that during physical activity when ketones are present, the body will continue to use more fat for energy producing more ketones and prompting a potential ketoacidosis state.  

Yet many say if you are high to exercise… So here is a general rule of thumb! 

• Blood sugar > 300 mg/dL → Check Ketones →  Negative → Get Moving
  • Heads up: if your sugar’s really high, you might feel like trash—and that’s okay. Don’t push it if your body says no. But sometimes light activity can help bring it down faster.
• Blood sugar > 300 mg/dL → Ketones Positive → Treat & Sit it Out   
  • Resume when ketones are negative ✅
    • If BG still > 250 mg/dL → stick to something chill (like walking).
    • If BG is 90–250 mg/dL → go for it! Resume your normal activity, no restrictions.

Glucose, Set, Go! 

Timing: 

At the end of the day, the best time to work out is… the time that actually works for YOU; but here are some pro tips based on type of diabetes:

• Type 1 diabetes: 
  • Morning workouts = Best time! They help keep blood sugars steadier all day + lower risk of lows.
  • Exercising right after meals? Be careful—it can cause double lows (insulin + exercise working at the same time).
• Type 2 diabetes:
  • After-meal exercise = Super helpful! It lowers those post-meal spikes.
    BUT if you’re on insulin, watch out for the “double effect” (insulin + exercise).

Order:

No one-size-fits-all, but research shows doing strength training (anaerobic) BEFORE cardio (aerobic) works best. Why? It helps prevent that big sugar drop that sometimes comes with cardio.

Snacking:

Prior to exercise, it is important to check where your blood sugar is at and to eat a snack with carbohydrates AND protein/fats to not only increase blood sugar prior to activity but also stabilize it. 

Amount of carbs you consume before an activity will depend on:  

• Starting blood sugar 
• Active insulin on board (remember, IOB time will be different depending on what type of insulin (inhaled, rapid acting, ultra-rapid acting) you use!)
• Length of activity 
• Intensity of activity  

An example would be if prior to activity that you know typically drops your blood sugar (spinning, pilates, morning jog), your blood sugar is 90 mg/dL. At this point, it is recommended to consume about 15 grams of carbohydrates (BEFORE exercise, followed by protein (insert examples here) for stabilization of blood sugar and monitor every hour during exercise.  

If using a pump, Tandem, Medtronic, and Omnipod all have activity mode which increases target to decrease basal movement during exercise and it is recommended to turn on 30 minutes prior and to leave on for 30 minutes after. If using iLet Beta Bionics, it is recommended to FIRST disconnect the pump, THEN consume carbohydrates if needed, and then continue to monitor.  

If not using insulin, hypoglycemia is rare. Since insulin isn’t on board, the risk of exercise-related hypoglycemia is much lower, so the focus is more on fueling and preventing post-exercise lows.

Press Pause, Play Strong

Yeah, it can feel awkward to step out during a game or a workout class—but checking your blood sugar or ketones is just like grabbing water: it keeps you in the game longer. Just like stretching and hydrating, checking your glucose is part of being a strong athlete.  

• Tell your coach or team early so it’s no big deal. 
• Keep your stuff handy so checks are quick. 
• Remember: a few minutes now beats sitting out for days later. 

Glucose Check, Now Self-Check 

Before exercising, ask yourself: Do I want to do this right now, or do I feel like I have to?

We have all been there – you notice your blood sugar is high and feel like you need to do a few squats or go for a walk to bring it down. Is the only reason you are exercising to “fix” a high blood sugar? If so, consider a safer or more enjoyable alternative. The idea is NOT to hate exercising and associate it with negative feelings; it is to keep you healthy mentally and physically.  

Checklist:  

• What exercise will I be doing? Do I expect high during or lows? 
• Where is my sugar? 
• Do I need to eat some carbs before exercise? 
• Do I have ketones? 
• How much insulin do I have on board? 
• Is my pump in activity mode? 
• Do I have my glucometer, CGM, and snacks close by?