December 4, 2025
Why Leftover Pizza May Actually Be Healthier
Researchers have found that refrigerating starchy foods—from pizza to rice—creates “resistant starch,” a carbohydrate that behaves like fiber and alters blood sugar response.
This video is part of “Innovations in: Type 1 Diabetes“, an editorially independent special report produced with financial support from Vertex.
Tom Lam: At first glance, it might look like a regular fun internet fact that you half remember and try to retell at a party, like…
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[Lum pretends to be a guest at a party. He is holding a slice of pizza and talking over music.]
Lam: Did you know that I read somewhere that leftover pizza is actually better… well… so how do you know Lauren?
But the secret is that this is just the surface of the fact, and the deeper we go, the funnier and weirder science becomes.
Because your first thought upon hearing this will probably be, “Why?” Why is leftover pizza better for me? And the answer has to do with what happens when you chill the delicious crust. When you cool pizza below 40 degrees Fahrenheit, some of the starches in the dough will begin to mix together, forming long chains called resistant starches.
They resist digestion, and a carbohydrate that resists digestion can be called fiber! And even if you reheat the pizza, the chains will remain intact and your body will not break them down into sugar. Mostly they pass.
This may help reduce blood sugar spikes in people with diabetes or people who simply need more fiber for gut health. And it seems to work for many starches, such as rice, pasta, potatoes, and even beans and lentils. Heating and subsequent cooling of starch changes its properties. It's like tempering chocolate or forging stronger steel.
But we can delve deeper into this fun fact because you may have another question: “How?” How did scientists study, analyze and figure this out? And for this we need to turn to real newspapers.
And here you'll find electron microscope photographs of old rice that show these long, starchy fibers forming and then clumping together through “simulated digestion.” And you'll also find human studies attempting to measure these changes in health, such as this one, where brave participants had to be in the lab at 6am to eat old rice for science, which they had to do so that nothing else they ate that day would interfere with their measurements.
This study also measured how long participants chewed the rice, which may seem excessive until they point out that digestion begins in the mouth. And it's this smart attention to detail that is the most important part, because that's how you get the interesting fact.
Like, humans have been eating food for as long as we have existed, but the way it interacts with our bodies is so complex that we just learned that apparently our refrigerator is a forge of fiber. And I think the details of the study are much more interesting than the fun fact. This may not be the best option for parties.
[Lum pretends to be a guest at a party again.]
Lam: Hello, this is Tom. Did you know that digestion begins in the mouth?
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