Eating a large amount of red meat in early adulthood could be associated with an increased risk of breast cancer, a new study suggests.
Substituting red meat with legumes - such as peas, beans and lentils - nuts, poultry, and fish could reduce the risk, they found.
Studies thus far have found no significant association between the consumption of red meat and breast cancer, but the team of US researchers said that most previous research has been based on diet during mid and later life.
So they decided to assess the dietary habits of 89,000 premenopausal women aged 26 to 43 in 1991.
Their study, published on bmj.com, examined frequency of red meat intake as well as other foods through a food frequency questionnaire.
The authors also assessed the women's adolescent food intake.
In the 20-year follow-up period, medical records identified 2,830 cases of breast cancer.
The researchers estimated that for each step-by-step increase in the women's consumption of red meat, there was a step-by-step increase in the risk of getting breast cancer.
Higher intake of red meat was associated with a 22% increased risk of breast cancer overall.
And each additional serving per day of red meat was associated with a 13% increase in risk of breast cancer, they said.
Substituting one serving of red meat each day of combined legumes, nuts, poultry, and fish was associated with a 14% lower risk of breast cancer, they said.
"Higher red meat intake in early adulthood may be a risk factor for breast cancer, and replacing red meat with a combination of legumes, poultry, nuts and fish may reduce the risk of breast cancer," the authors concluded.
But other experts cautioned that the findings should be interpreted with caution.
Professor Valerie Beral, professor of epidemiology and director of the Cancer Epidemiology Unit at the University of Oxford, said: "Dozens and dozens of studies have looked at breast cancer risk associated with some aspect of diet. The totality of the available evidence indicates that red meat consumption has little or no effect on breast cancer risk, so results from a single study cannot be considered in isolation.
"Diet is notoriously difficult to measure. The most reliable measure of meat consumption is whether or not people are vegetarian. Vegetarians do not have lower risks of breast cancer than non-vegetarians, further supporting other evidence that meat consumption is unlikely to play a major role in breast cancer."
Professor Tim Key, a Cancer Research UK epidemiologist based at the University of Oxford, added: "This research finds only a weak link between eating red meat and breast cancer and this study alone is not strong enough to change the existing evidence that has found no definite link between the two.
"Further studies are needed to clarify whether younger women who eat red meat have an increased risk of developing breast cancer.
"Women can reduce their risk of breast cancer by maintaining a healthy weight, drinking less alcohol and being physically active, and it's not a bad idea to swap some red meat - which is linked to bowel cancer - for white meat, beans or fish."
Sally Greenbrook, senior policy officer at charity Breakthrough Breast Cancer, said: "We don't yet know enough about the link between breast cancer and diet so this is quite an interesting study. We would welcome more research into this in order to help us identify what kind of impact red meat could have on breast cancer risk.
"It's important that everybody follows a varied, balanced diet for general health and wellbeing - this includes fruits, vegetables, pulses and whole grains, and limited red meat, processed meat, animal fat, sugary or fatty processed food, salt and alcohol.
"It's already been proven that women can reduce their breast cancer risk by maintaining a healthy weight, reducing alcohol consumption and increasing the amount of physical activity they do."