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Dietary protein sources in early adulthood and breast cancer incidence: prospective cohort study

BMJ 2014; 348 doi: (Published 10 June 2014) Cite this as: BMJ 2014;348:g3437
  1. Maryam S Farvid, Takemi fellow, and associate professor12,
  2. Eunyoung Cho, associate professor34,
  3. Wendy Y Chen, assistant professor45,
  4. A Heather Eliassen, assistant professor 46,
  5. Walter C Willett, professor146
  1. 1Department of Nutrition, Harvard School of Public Health, Boston 02115, MA, USA
  2. 2Department of Community Nutrition, Faculty of Nutrition Sciences and Food Technology, Shahid Beheshti University of Medical Sciences, Tehran, Iran
  3. 3Department of Dermatology, The Warren Alpert Medical School of Brown University, Providence, RI, USA
  4. 4Channing Division of Network Medicine, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School, Boston, MA, USA
  5. 5Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA, USA
  6. 6Department of Epidemiology, Harvard School of Public Health, Boston, MA, USA
  1. Correspondence to: M S Farvid mfarvid{at}
  • Accepted 14 May 2014


Objective To investigate the association between dietary protein sources in early adulthood and risk of breast cancer.

Design Prospective cohort study.

Setting Health professionals in the United States.

Participants 88 803 premenopausal women from the Nurses’ Health Study II who completed a questionnaire on diet in 1991.

Main outcome measure Incident cases of invasive breast carcinoma, identified through self report and confirmed by pathology report.

Results We documented 2830 cases of breast cancer during 20 years of follow-up. Higher intake of total red meat was associated with an increased risk of breast cancer overall (relative risk 1.22, 95% confidence interval 1.06 to 1.40; Ptrend=0.01, for highest fifth v lowest fifth of intake). However, higher intakes of poultry, fish, eggs, legumes, and nuts were not related to breast cancer overall. When the association was evaluated by menopausal status, higher intake of poultry was associated with a lower risk of breast cancer in postmenopausal women (0.73, 0.58 to 0.91; Ptrend=0.02, for highest fifth v lowest fifth of intake) but not in premenopausal women (0.93, 0.78 to 1.11; Ptrend=0.60, for highest fifth v lowest fifth of intake). In estimating the effects of exchanging different protein sources, substituting one serving/day of legumes for one serving/day of red meat was associated with a 15% lower risk of breast cancer among all women (0.85, 0.73 to 0.98) and a 19% lower risk among premenopausal women (0.81, 0.66 to 0.99). Also, substituting one serving/day of poultry for one serving/day of red meat was associated with a 17% lower risk of breast cancer overall (0.83, 0.72 to 0.96) and a 24% lower risk of postmenopausal breast cancer (0.76, 0.59 to 0.99). Furthermore, substituting one serving/day of combined legumes, nuts, poultry, and fish for one serving/day of red meat was associated with a 14% lower risk of breast cancer overall (0.86, 0.78 to 0.94) and premenopausal breast cancer (0.86, 0.76 to 0.98).

Conclusion 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.


  • We thank the participants and staff of the Nurses’ Health Study II; the following state cancer registries for their help AL, AZ, AR, CA, CO, CT, DE, FL, GA, ID, IL, IN, IA, KY, LA, ME, MD, MA, MI, NE, NH, NJ, NY, NC, ND, OH, OK, OR, PA, RI, SC, TN, TX, VA, WA, WY; and the Connecticut Department of Public Health Human Investigations Committee, which approved this study. Certain data used in this publication were obtained from the Department of Public Health.

  • Contributors: MSF, EC, WYC, AHE, and WCW designed the research. MSF carried out the analysis and wrote the manuscript. All authors provided critical input in the writing of the manuscript and read and approved the final version of manuscript. MSF and WCW are the guarantors.

  • Funding: This study was supported by the National Institutes of Health grant (R01CA050385). The study sponsors were not involved in the study design and collection, analysis, and interpretation of data, or the writing of the article or the decision to submit it for publication. The authors were independent from study sponsors.

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at (available on request from the corresponding author) and declare: no support from any organization for the submitted work; no financial relationships with any organizations that might have an interest in the submitted work in the previous three years, no other relationships or activities that could appear to have influenced the submitted work.

  • Ethical approval: The study protocol (institutional review board No 1999-P-003389) was approved by the institutional review boards of Brigham and Women’s Hospital and Harvard School of Public Health. The completion of the self administered questionnaire was considered to imply informed consent.

  • Data sharing: No additional data available.

  • Transparency: MSF and WCW affirm that the manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.

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