Experts said that both studies were large and carefully conducted and thus important in better defining the often murky relationship between cancer and people's eating habits — with implications for consumers.

The study on meat and cancer, published today in the Journal of the American Medical Assn., was conducted by Ann Chao of the American Cancer Society and colleagues using data from 148,610 men and women aged 50 to 74 in 21 states.

The scientists found that the group that ate the most red meat over the long term (defined as an average of at least three ounces daily for men and two ounces for women) had a 30% to 40% increased risk of rectal cancer or cancer of the distal colon (the portion of the colon nearest the rectum) compared to those whose consumption was lowest (less than 1.5 ounces daily for men, and one ounce for women.)

High consumption of processed meats was associated with a 50% increase in cancers of the distal colon. There were 1,667 colorectal cancers during the course of the study.

"If you're going to eat red meat, you should choose smaller portions, leaner cuts, and you should try to get your protein less from red and processed meats and more from fish, poultry, nuts and beans, " said Eugenia Calle, senior author of the paper and director of analytic epidemiology at the American Cancer Society.

Calle said that scientists do not know enough to recommend a maximum daily intake of red meat, or what component of the meat might cause risk: It might be fat, nitrates, cancer-promoting chemicals caused via cooking, or some other factor.

The second study, also published in the medical journal, was conducted by a team of scientists based at the University Medical Center in Utrecht, in the Netherlands. The study looked at women aged 25 to 70 from 10 European countries with very different patterns of fruit and vegetable consumption.

By 2002, the researchers recorded 3,659 new cases of breast cancer in the group. The rate was no different for those who ate many or few fruits and vegetables.

Dr. Petra M. Peeters, a principal investigator on the study and an epidemiologist at the University Medical Center, said the finding was in line with several recent studies.

Dr. Walter Willett, professor of epidemiology and nutrition at Harvard School of Public Health, who wrote a commentary accompanying the two reports, said people should still eat lots of fruits and vegetables.

"The benefits are quite clear for reducing risk of heart disease and that's the No. 1 killer of both men and women," he said.