U.S. food researchers have found a process that makes pizza a healthier-to-eat food by increasing the antioxidants in whole-grain wheat pizza dough.

Antioxidants are substances that protect cells from damage caused by unstable molecules known as free radicals. Some experts believe antioxidants can lower the risk of cancer, heart disease and other ailments.

University of Maryland food chemists said Monday they had enhanced the antioxidant content of whole-grain wheat pizza dough by baking it longer at higher temperatures and giving the dough more time to rise.

"The reason that we chose pizza is just because it is a very popular food product, not only in the U.S. but worldwide," researcher Jeffrey Moore said. "So we thought if we could find ways to improve (its antioxidant) properties, doing this for such a product could have a larger impact on public health."

But Moore said fatty toppings like extra cheese, pepperoni, sausage and ground beef erase nutritional benefits gained by the increase in oxidants.

"If you're adding back all these other things that have potential negative health consequences, then you're negating anything that you're adding in terms of (health) value," Moore explained.

The research was reported at a meeting of the American Chemical Society in Chicago. The researchers experimented with baking temperatures, baking time and fermentation time -- the time the pizza dough is given to rise.

Antioxidant levels rose as much as 60 percent with longer baking times and up to 82 percent with higher baking temperatures, depending on the type of wheat flour and the antioxidant test used, they said. The precise mechanisms involved are unclear, they said.

They looked at fermentation times up to two full days, and found longer periods in some cases doubled the dough's antioxidant levels. This probably stemmed from chemical reactions caused by yeasts in the dough that had more time to release the antioxidant components, Moore said.

A common fermentation time is about 18 hours, Moore said.

The study used only whole wheat dough. Most of the antioxidants in wheat are in the bran and endosperm components that are generally removed in refined flour, Moore said. Longer and hotter baking and longer fermentation likely would be less effective in making more healthful pizza with refined flour, he said.

The study was funded by the U.S. Department of Agriculture and grain organizations, but not by the pizza industry.