Exercise and Blood Sugar: What They Didn’t Tell You at Diagnosis

You were told about carbs and insulin. Maybe even ratios. But exercise? Probably not.

Episode 755 of The Juicebox Podcast digs into what every person with type 1 diabetes discovers too late — that moving your body doesn’t follow one rule, and that the right kind of movement can send your blood sugar up or down depending on the type.

The Lesson No One Gives You

When you’re newly diagnosed, the list of “don’ts” is long. Exercise barely makes the list.
Doctors say, “Be careful.” But careful doesn’t mean informed.

Certified Diabetes Care and Education Specialist Jennifer Smith joins Scott Benner to explain why understanding exercise is as important as understanding insulin.

“It’s a neglected topic,” Jenny says. “You’re so busy learning everything else that movement ends up at the bottom of the list.”

And yet, it affects everything — timing, insulin needs, and safety.

Two Kinds of Exercise, Two Very Different Results

Scott jokes about “aerobic” versus “anaerobic” — running versus lifting — and Jenny laughs, but the truth behind it matters.

Aerobic (cardio) — running, biking, swimming, jumping on a trampoline — uses oxygen and tends to lower blood sugar.
Anaerobic (resistance) — weight training, sprints, heavy effort — triggers adrenaline and can raise blood sugar.

“The heavier the load,” Jenny explains, “the more adrenaline. That’s often what pushes numbers up.”Bold Beginnings 755

And real life rarely fits neatly into one category.
Your kid runs up and down the stairs 40 times after dinner — that’s aerobic.
But what if they also lift a heavy backpack? Now it’s both.

The Surprising Everyday Triggers

Exercise isn’t just the gym. It’s mowing the lawn, cleaning the house, chasing your dog, or walking through Target. Anything that raises your activity above baseline changes how your body uses insulin.

Scott sums it up:

“Your insulin settings are made for sitting at work or school — not for chasing kids or cleaning the garage.”Bold Beginnings 755

That means a “normal” day can suddenly become an exercise day — and if there’s active insulin on board, lows can hit fast.

Why Some Activities Make You Drop

Aerobic activity speeds up insulin use. If there’s a lot of active insulin, your body pulls glucose out of your blood faster — what Scott calls a “pull,” not a “drop.”Bold Beginnings 755

Fifteen to twenty minutes into cardio is the danger window. You might be fine at first, then suddenly sliding.

Jenny puts it simply:

“If you haven’t planned for it — no carb, no insulin adjustment — around 15 minutes is when it starts to nudge down.”Bold Beginnings 755

The Role of Adrenaline and Emotion

Here’s the twist: not all activity lowers blood sugar.
Competition and intensity can raise it.

A baseball game might spike you, while practice keeps you steady.
Why? Adrenaline.

“Games trigger excitement,” Jenny says. “That rush pushes glucose up.”Bold Beginnings 755

It’s not unpredictable — it’s physiology.

What Happens When Nobody Explains It

One listener wrote:

“My son was in baseball and swimming when he was diagnosed. The doctor told us he’d have to rethink his sports. I thought he couldn’t live a normal life.”Bold Beginnings 755

That kind of advice sticks — and it’s wrong.
People with type 1 diabetes run marathons, play in the NFL, and lift competitively.
Exercise isn’t off-limits. It just requires awareness.

Five Things That Make Exercise Work With Diabetes

1. Avoid aerobic exercise with active insulin on board.
   If you just ate, wait. Active insulin + movement = rapid lows.

2. Carry carbs — always.
   Even quick, unplanned activity (like chasing kids) burns glucose fast.

3. Plan for planned movement.
   Lower basal before workouts or reduce meal boluses ahead of time.

4. Expect adrenaline spikes.
   Sports, lifting, or competition may raise glucose — you might even need a small bolus.

5. Know your pattern, not just your number.
   CGMs reveal whether you’re falling or steady; your response should match your trend.

What It Really Means

Exercise shouldn’t feel dangerous.
When you understand what’s happening — that movement changes how insulin behaves — you can stop guessing and start planning.

The goal isn’t avoiding activity; it’s owning it.

Listen to Bold Beginnings: Exercise (Episode 755) wherever you get podcasts, and learn how to make movement part of your diabetes toolkit — not something to fear.

References

1. Riddell MC et al. Exercise Management in Type 1 Diabetes: A Consensus Statement. Lancet Diabetes Endocrinol, 2017.

2. American Diabetes Association. Standards of Care in Diabetes 2025: Physical Activity.

3. Yardley JE et al. Managing Exercise in Type 1 Diabetes: Practical Strategies for the Real World. Diabetes Spectrum, 2020.