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Walter C. Willett, MD, DrPH

Harvard Medical School
Boston, Massachusetts

Titles and Affiliations

Professor of Epidemiology and Nutrition
Department of Nutrition
Harvard T.H. Chan School of Public Health
Boston, Massachusetts

Research area

Understanding the effects of diet and gut microbial health on breast cancer risk.


Lifestyle choices, including diet, can play a pivotal role in breast cancer prevention. Diets rich in vegetables, fruits, whole grains, fish, and olive oil have consistently been associated with a decreased risk of breast cancer. Recent studies have suggested that the microbiome—the collection of millions of intestinal bacteria—plays an important role in modulating risk of several chronic diseases, including breast cancer, by altering estrogen metabolism. At the same time, it is now understood that diet plays a significant role in shaping the microbiome and its overall health. Dr. Willett is examining relationships between diet and breast cancer risk to identify ways to reduce risk and mortality from this disease.

Progress thus far

Dr. Willet and his team are conducting their research in cohorts of women whose lifestyle and dietary choices have been followed for decades using methods such as questionnaires and collection of blood and fecal (stool) samples from participants. Ongoing studies include: 1) examining variability in the gut microbiome over time to understand its role in breast cancer risk and prevention; 2) evaluating dietary data from 20 large cohort studies from around the world to determine whether higher intake of fruits and vegetables, particularly cruciferous ones such as broccoli or cauliflower, are associated with reduced risk of breast cancer. In preliminary analyses, consuming greater amounts of total fruit and vegetables is modestly associated with reduced breast cancer risk; 3) combining diet and breast cancer analyses to expand racial and socioeconomic diversity; and 4) calibrating dietary questionnaires used across studies to standardize cohort data.

What’s next

In the coming year, Dr. Willett will examine the microbiome data to characterize variability, continue his analyses of cohort data, incorporating diet data, interactions with menopausal status, diagnosis age, and evaluating associations by molecular subtype of breast cancer, and continue the analysis of data from the fruit/vegetable subgroups, evaluating interactions by age, risk factors, and molecular subtype of breast cancer.


Dr. Walter Willett is Professor of Epidemiology and Nutrition at the Harvard T.H. Chan School of Public Health and Professor of Medicine at Harvard Medical School. Dr. Willett was born in Hart, Michigan and grew up in Madison, Wisconsin, studied food science at Michigan State University, and graduated from the University of Michigan Medical School before obtaining a Doctorate in Public Health from Harvard School of Public Health.

Dr. Willett has focused much of his work over the last 40 years on the development of methods, using both questionnaire and biochemical approaches, to study the effects of diet on the occurrence of major diseases. He has applied these methods starting in 1980 in the Nurses’ Health Studies I and II and the Health Professionals Follow-up Study. Together, these cohorts that include nearly 300,000 men and women with repeated dietary assessments are providing the most detailed information on the long-term health consequences of food choices.

Dr. Willett has published over 2,000 articles, primarily on lifestyle risk factors for heart disease and cancer, and has written the textbook, Nutritional Epidemiology, published by Oxford University Press. He also has four books book for the general public, Eat, Drink and Be Healthy: The Harvard Medical School Guide to Healthy Eating, which has appeared on most major bestseller lists, Eat, Drink, and Weigh Less, co-authored with Mollie Katzen, The Fertility Diet, co-authored with Jorge Chavarro and Pat Skerrett, and most recently, Thinfluence, co-authored with Malissa Wood, emphasizing the powerful and surprising effect friends, family, work, and environment have on weight. Dr. Willett is the most cited nutritionist internationally and is among the five most cited persons in all fields of clinical science. He is a member of the National Academy of Sciences and the recipient of many national and international awards for his research.

BCRF Investigator Since


Donor Recognition

The Hale Family Award