The research, published in the British Medical Journal (BMJ), investigated the association between dietary protein sources in early adulthood and risk of breast cancer in more than 80,000 women who took part in the Nurses' Health Study II in 1991.
Led by Dr Maryam Farvid from the Harvard School of Public Health, the research team found that higher consumption of red meat in women during early adulthood was associated with a higher risk of breast cancer, while poultry intake was associated with a lower risk of breast cancer in postmenopausal women.
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,” concluded the research team.
“Although intakes of legumes, fish, eggs, and nuts were not significantly associated with breast cancer in either premenopausal or postmenopausal women, substituting legumes or poultry or the combination of poultry, fish, legumes, and nuts for red meat was associated with a lower risk of breast cancer,” they said.
Favid and her colleagues noted that in the current study, each serving per day increase in red meat was associated with a 13% relative increase in risk of breast cancer.
"When this relatively small relative risk is applied to breast cancer, which has a high lifetime incidence, the absolute number of excess cases attributable to red meat intake would be substantial, and hence a public health concern," they said.
The US-based researchers noted that so far, studies have suggested no significant association between red meat intake and breast cancer.
However, most have been based on diet during midlife and later, they explained, adding other evidence suggests that some exposures, potentially including dietary factors, could affect the development of breast cancer during early adulthood.
As a result, the team analysed 20 year follow-up data from 88,803 premenopausal women (aged 26 to 45) taking part in the Nurses' Health Study II.
Red meat items included unprocessed red meat (beef, pork, or lamb and hamburger) and processed red meat (hot dogs, bacon and sausage); poultry included chicken and turkey; fish included tuna, salmon, mackerel, sardines; legumes included beans, lentils and peas; and nuts.
Factors including height, weight, race, family history of breast cancer, history of benign breast disease, smoking, menopausal status, hormone and oral contraceptive use were taken into account.
Medical records identified 2,830 cases of breast cancer during 20 years of follow-up. Putting this real life data into a statistical model allowed the researchers to estimate breast cancer risks for women with different diets.
The found that for each step-by-step increase in the women's consumption of red meat there was an increase in the risk of getting breast cancer over the 20 year study period.
This translated to an estimate that higher intake of red meat was associated with a 22% increased risk of breast cancer overall – with each additional serving per day of red meat associated with a 13% increase in risk of breast cancer (12% in premenopausal and 8% in postmenopausal women).
In contrast, the estimates showed a lower risk of breast cancer in postmenopausal women with higher consumption of poultry. Substituting one serving per day of poultry for one serving per day of red meat - in the statistical model - was associated with a 17% lower risk of breast cancer overall and a 24% lower risk of postmenopausal breast cancer, said the team.
Furthermore, substituting one serving per day of combined legumes, nuts, poultry, and fish for one serving per day of red meat was associated with a 14% lower risk of breast cancer overall and premenopausal breast cancer.
Volume 348 doi: 10.1136/bmj.g3437
“Dietary protein sources in early adulthood and breast cancer incidence: prospective cohort study”
Authors: Maryam S Farvid, Eunyoung Cho, et al