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Type 1 Diabetes

Why Your Glucose Spikes After Pizza (Even When You Count)

· 3 min read · Reviewed by GlucIQ Clinical Review Workflow
#post-meal-glucose#insulin-timing#cluster:bolus-math

It’s 8pm. You counted the pizza slices, dosed for the crust and the sauce, and ate. By 9:30 your CGM is creeping up. By 11pm you’re at 200 — and your insulin from dinner has already done its job and faded.

Sound familiar? Here’s the thing: you didn’t do the math wrong. The pizza just plays by different rules.

The spike has two waves

Carbs hit fast. That’s the first wave — the one your insulin covers.

But fat and protein hit slow. Hours later, they’re still nudging your glucose up. That’s the second wave — the one nobody told you about.

Studies back this up. One showed fat can nearly double how much insulin a meal needs (Wolpert et al., 2013). Another found protein and fat both raise glucose, and they stack on top of each other (Smart et al., 2013). Pizza is basically a fat-and-protein delivery system wearing a carb costume.

How to know if it’s the second wave

Look at your curve, not your number:

  • Spike at 1-2 hours? That’s the carbs. Your bolus timing is the lever.
  • Climb starting 3-5 hours after you eat? That’s the second wave. Fat and protein.
  • Both? Double-wave meal. Very normal, very fixable.

The 70-180 “safe zone” that the experts use (Battelino et al., 2019) counts all of that time — including the 11pm wave from dinner. So yes, it matters.

What actually helps

1. Bolus earlier, not bigger. A dose that lands 10-15 minutes before you eat covers the first wave better. Small change, big difference.

2. Ask about the “extended” bolus. Pumps have a setting that dribbles insulin out over hours instead of all at once. It’s made for exactly this — the second wave. Not every meal needs it, but pizza night does.

3. Don’t stack corrections at 11pm. The second wave is still rising. One correction, then wait. Stacking just sets up a low for 2am.

4. Learn your pizza curve. Same restaurant, same order, three times — and you’ll know exactly what your body does. That’s not boring. That’s data.

The one-minute takeaway

You’re not bad at carb counting. Mixed meals just need more than a carb count. Fat and protein add a slow second wave — and once you know it’s there, you can dose for it.

Talk to your care team before changing how you bolus. And next pizza night, give the extended bolus a try — with their blessing.

References

  • Smart CE, et al. Both dietary protein and fat increase postprandial glucose excursions in children with type 1 diabetes. Diabetes Care. 2013. DOI: 10.2337/dc13-1195
  • Wolpert HA, et al. Dietary fat acutely increases glucose concentrations and insulin requirements in patients with type 1 diabetes. Diabetes Care. 2013. DOI: 10.2337/dc12-0092
  • Battelino T, et al. Clinical Targets for CGM Data Interpretation: International Consensus on Time in Range. Diabetes Care. 2019. DOI: 10.2337/dci19-0028