You’ve probably never heard it before: “Leftover pizza is better for you than fresh.” It sounds like the kind of half-baked trivia someone blurts out at a party while holding a slice. But this one’s got some solid science behind it.

Researchers have found that cooling certain starchy foods, like pizza, rice, and pasta, actually changes their chemistry in a way that makes them healthier. The trick? Cooling them down creates something called “resistant starch,” a form of carbohydrate that behaves more like fiber in the body. And it could have real benefits, especially for people with Type 1 diabetes.

Here’s how it works.

When starchy foods like pizza crust are cooled to below 4°C (about 40°F), some of their starches reorganize into longer chains. These chains form what scientists call resistant starches, which don’t break down during digestion the way regular starches do. Instead of being absorbed as sugar, they pass through the digestive system more like dietary fiber.

Even if you reheat the food later, the new structure mostly sticks around.

That’s a big deal for anyone who needs to manage blood sugar levels. Resistant starch doesn’t cause the same spikes in glucose that normal carbs do. It also feeds the good bacteria in your gut and may improve overall digestive health. The process is a bit like tempering chocolate or forging steel—the heating and cooling changes the material at a molecular level.

And it isn’t just pizza. The effect shows up in rice, potatoes, pasta, beans, lentils, and other common staples. Reheating won’t undo the transformation, making your leftovers potentially a healthier choice than the original meal.

The science behind this isn’t just theoretical. It’s been studied in labs in detail. In one experiment, researchers used electron microscopes to examine rice after it had been cooked, cooled, and digested in simulated conditions. They found those long, sturdy chains of resistant starch still intact even after simulated digestion.

In another study, researchers went a step further. Human volunteers showed up at a lab at 6 in the morning to eat pre-cooked, chilled rice, all in the name of science. Researchers controlled every variable, including how long each participant chewed their rice. It might sound like overkill, but the scientists had a good reason: digestion begins in the mouth, and chewing plays a role in how foods break down.

That kind of rigor is exactly what turns a passing fun fact into a meaningful discovery.

“Humans have been eating food the entire time humans have existed,” said Tom Lum, a science communicator featured in the video series Innovations In: Type 1 Diabetes. “But the way it interacts with our body is so complex that we’ve only just learned that apparently our fridge is a forge for fiber.”

While you might not win any friends at a party by explaining starch crystallization and digestive enzymes, the takeaway is simple: chilling your leftovers could be a small, easy way to support better health. Especially for people living with diabetes, it might offer one more tool for keeping blood sugar in check.

So next time you open the fridge for cold pizza, remember—it’s not just tasty. It might actually be helping your body, one slice at a time.