Washington ? A diet rich in tomato sauce, ketchup and other tomato-based products containing a powerful antioxidant can lower the risk of prostate cancer, a new study says.

Researchers analyzed the food choices and prostate cancer histories of more than 47,000 men and found that those who ate at least two meals a week containing tomato products lowered their risk of prostate cancer by 24 percent to 36 percent.

Dr. Edward Giovannucci of Brigham and Women’s Hospital and the Harvard School of Public Health, the first author of the study, said it supports earlier research involving foods, particularly tomato products, that were high in lycopene, a powerful antioxidant.

“These most recent finding add support to the notion that a diet rich in tomatoes and lycopene-containing foods, as well as other fruits and vegetables, may reduce the risk of prostate cancer,” said Giovannucci.

A report on the study appears today in the Journal of the National Cancer Institute.

Giovannucci said that lycopene is thought to protect against cancer by absorbing oxygen-free radicals, which are chemicals created during metabolism that can damage the genetic structure of cells.

The finding is based on data from the Health Professional Follow-Up Study, a project that followed the health history and dietary habits of 47,000 men, aged 40 to 75, from 1986 to 1998. During that period, 2,481 of the men developed prostate cancer.

Dietary questionnaires in the study included such food items as tomatoes, tomato sauce, tomato juice and pizza, along with salsa, ketchup and other tomato-based condiments.

When data were adjusted for effects of other lifestyle factors, researchers found that tomatoes, particularly those that had been cooked, were beneficial against prostate cancer.

“Spaghetti sauce was the most popular” and also seemed to give the most protection, said Giovannucci.