A new study has found that young women with diets high in meats, cheeses and other foods rich in animal fat may have a higher risk of developing breast cancer.

Researchers at Brigham and Women's Hospital, a teaching hospital of Harvard Medical School, found no link between breast cancer and plant-based fats such as olive oil, but they found a slight increase in breast cancer in women who ate more red meat and high-fat dairy products.

In the study, 90,000 nurses between the ages of 26 and 46 filled out a detailed questionnaire about their eating habits in 1991 and again in 1995. The researchers later looked at who had developed breast cancer -- and what they ate.

By 1999, 714 of the women involved in the study had developed breast cancer -- 134 in the group with the highest intake of animal fat, and 123 in the lowest group. While the difference between the two may seem small, Dr. Eunyoung Cho, one of the study's authors, says it is quite significant.

The women in the study who were most at risk obtained about 23 per cent of their total calories from fat, compared to 12 per cent in the lower risk group.

But Dr. Sandra Messner, a breast cancer specialist at Sunnybrook and Women's Health Sciences Centre, told CTV's Canada AM that women don't need to cut out meat and other animal-based foods altogether to reduce the risk of breast cancer.

"One of my concerns when studies like this come out is that women will stop eating meat and they won't get their iron, they won't get their zinc, they will stop eating dairy, they won't get their calcium. You have to balance foods out," Messner said.

She said women should focus on getting colourful, plant-based foods such as sweet potatoes and blueberries into their diets.

"There's always been a sense from the literature that a diet that's more heavily plant-based is better," Messner said. "We know that women in Asian countries, for instance, have a much lower rate of breast cancer than women in North America.

"It was always a question, was it because they ate more soy or was it because they ate less of something else? I think this is really just confirming the sense that we already had before."

But she added that people should be cautious and not use the study as a basis for saying animal fats actually cause breast cancer.

"I don't think anyone actually knows that there's a cause and effect," Messner said. "It's more an association -- we know that if you eat more animal fats, the risk seems to be higher."

Researchers say it's possible substances other than the fat in animal-based foods may in fact be the culprit.