Dr Walter Willett is Professor of Epidemiology and Nutrition and Chairman of the Department of Nutrition at the Harvard T.H. Chan School of Public Health and Professor of Medicine at Harvard Medical School. Dr Willett studied food science at Michigan State University, and graduated from the University of Michigan Medical School before obtaining a Doctorate in Public Health from the Harvard School of Public Health. Dr Willett has focused much of his work over the last 35 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 1500 articles, primarily on lifestyle risk factors for heart disease and cancer. 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 Institute of Medicine of the National Academy of Sciences and the recipient of many national and international awards for his research.

Diet, weight control and energy balance in cancer

The topic of diet and cancer has been the focus of much research since the early 1980’s when Doll and Peto suggested that about 35% of cancer might be caused by, or prevented by, dietary factors.  At that time total dietary fat was believed to be the most important factor underlying the high rates of many cancers in western countries.  Since then, large prospective studies and several randomized trials have not supported dietary fat, at least during midlife and later, as an important cause of cancer.   Also, initial enthusiasm for a major role of fruits and vegetables in prevention of cancer has been tempered by the results of prospective studies showing little or no relation with overall cancer incidence, although some benefit for specific subsets of cancer has been documented.  In contrast with these studies, excess body fat and particularly weight gain during adult life has been shown to be a major cause of many types of cancer, ranking close to smoking as a potentially modifiable cause of cancer in some populations.  Considerable evidence suggests that other specific dietary factors including soy foods, specific carotenoids, and dairy products also contribute to the cause and prevention of specific cancer.  Importantly, the role of diet during childhood, adolescence, and early adult life in the etiology of cancers diagnosed decades later has been minimally studied, but recent findings suggest that reducing  consumption of red meat and increasing intakes of fruits, vegetables, whole grains, and soy products could reduce risk of breast cancer.