More insulin means more lows. This goes back to The Law of Small Numbers:

“Big inputs make big mistakes; small inputs make small mistakes.”

The more insulin you have floating around in your system, the higher the chance of a dose gone wrong (it comes down to variables). Seems intuitive, right? But I’m not talking about lows 2 hours after eating. I’m talking lows that we may not even realize correspond to our insulin dosing.

This is because while they tell you the duration of action for insulin aspart/lispro (your fast-acting, mealtime, Novolog/Humalog insulins) is 3-4h for practical purposes, it’s not actually that short. In reality, it has a lifespan that’s really closer to 6, even 7 hours. That’s up to an additional 4 hours of having insulin in your system that you didn’t think you had!

This is why I preach that what your blood sugars do during exercise has to do with what you’ve done over the past 6-7h. Too much insulin, and you’ll go low. Normal amounts or not enough? You’ll spike.

Now that I’m on automode on my insulin pump, consistently receiving a physiologic basal (read: never too much insulin), I rarely go low, and even more rarely go low on runs (instead, I now spike).

Why Correcting Carbs With Insulin Never Works

But yesterday morning, I ate more carbs for breakfast than I sometimes do in one day. So I took more insulin than I usually do. It did its job for that moment.

But then, it actually ended up being too much insulin because I didn’t pre-bolus (give myself my insulin before I started to eat) and was kind of aggressively chasing a spike that happened because my carb-intake didn’t match my insulin-intake.

Per usual, the culprit is carbs. 

So when I set out for my run at 2:30pm, I knew that all that insulin from 7:30am at breakfast was going to catch back up with me, despite the fact that my blood sugars were perfect. I’d literally only eaten veggies for lunch and had only had very minimal basal insulin in the background since breakfast.

But that’s just what large amounts of insulin do. They cause lows. All the time, always. 

So I ate before my run. Because after years of running with type 1 diabetes I knew I would drop in this situation, based on the preceding 6-7h.

I ate 20g of carbohydrates beforehand, started at 86 mg/dL, and ended at 67 mg/dL. I didn’t have a post-exercise spike, because when you have too much insulin-on-board, you are basically covering for the natural blood sugar spike.

Between 13 years of distance running and life with type 1 diabetes (plus a strong science background), I’ve figured out how to predict pretty accurately what is going to happen to my blood sugars during exercise.

And it boils down to this: more insulin, more problems - I mean, lows!