The Man Who Built a Bridge from Epidemiology to Nutrition

The Man Who Built a Bridge from Epidemiology to Nutrition

The second-most cited author in clinical medicine has not always been revered.

Walter C. Willett

Fredrick John Stare Professor of Epidemiology and Nutrition and Chair, Department of Nutrition, Harvard School of Public Health; Professor of Medicine, Harvard Medical School; Principal Investigator, The Second Nurses' Health Study and The Health Professional's Follow-up Study
Academy member since: 1997
MD: University of Michigan Medical School, 1970. MPH: Harvard School of Public Health, 1973. DrPH: Harvard School of Public Health, Epidemiology, 1980
Books: Nutritional Epidemiology (1998), Eat, Drink and Be Healthy: The Harvard Medical School Guide To Healthy Eating (2005), Eat, Drink, and Weigh Less (2007), The Fertility Diet (2008)
Also enjoys: Bicycling to work, an annual bike ride from Cambridge to Provincetown, Mass., advocating for bicycle friendly streets in Cambridge and Boston, and teaching public health and epidemiology in Dar es Salaam, Tanzania

I grew up in Wisconsin and Michigan in a family that has been dairy farming for generations. While studying at Michigan State University, I grew vegetables—sweet corn, tomatoes, squash—that I sold to local grocery stores to support my studies.

I started off there in physics and food science. I went on to medical school, but took several electives on nutrition-related topics. I spent one summer on an Indian reservation in the Upper Peninsula of Michigan doing a health and nutrition survey. I was shocked that 50 percent of adults in our survey had type-2 diabetes, and the study demonstrated to me how it was possible to collect very interesting and useful data about people's diets with a simple structured questionnaire.

My papers on how diet relates to long-term health and disease have led to being the second-most-cited author in clinical medicine. Much of this work was conducted within the Nurses' Health Study, which has provided a tremendous platform that continues to yield an expanding output of data as the subjects grow older.

The original focus of the study was breast cancer, but that allowed us to get funding to collect dietary data starting in 1980. The Nurses' Health Study was the first large study to gather dietary data and follow a large number of people for many different outcomes. It's also unique for having repeatedly updated dietary data every four years over time.

Many of our findings flew in the face of conventional wisdom. I was interested in the 1970's in the relationship between diet and cardiovascular disease and people were being told very strongly, as though it was absolutely established truth, that we should avoid eggs to prevent heart disease and give up saturated fat. When I dug into the literature supporting this, it was remarkably weak. In fact, there were no studies that showed that people who ate more eggs had higher risk of heart attacks, and the few small studies showed no relationship. It became apparent to me that a strong body of empirical evidence was needed if we were going to be giving guidance to individuals or the public.

During that time, several epidemiologists were documenting that rates of many cancers around the world varied tremendously. For example, the rates of breast cancer in post-menopausal women in Japan were only about one-eighth of those in the U.S. That obviously provokes the question, why? When I was in medical school, no one really asked why these things were happening, why people get cancer. When I went to the Harvard School of Public Health, people in the Department of Epidemiology were asking those questions.

The Department Chair at the time, Brian MacMahon, said there were some suggestions that diet might be important in the cause or prevention of cancer. That sounded like a pretty radical statement. The evidence was very scattered and not very strong, but the topic seemed worth investigating. What has unfolded has been surprising. Many strongly held beliefs, such as the relationship between eggs and coronary heart disease, turned out not to be supported.

One of the first findings to emerge was that alcohol consumption was related to breast cancer. That was highly controversial at first, but the finding has been replicated repeatedly and it's accepted now. There had been a belief that the percentage of calories from fat in the diet was the main reason why breast cancer rates were higher in the U.S. than in Japan and in developing countries. That idea turned out to be not supported by the data. Trans fats appeared early on as a problem. Experts in the cardiovascular field had been telling people to replace butter with margarine and Crisco to reduce cholesterol and saturated fat. But it turned out that those foods were very high in trans fats and were even worse than the foods they were meant to be replacing.

I was attacked, but most of these findings have become accepted with time. It took about 10 years to get FDA to require that trans fats be included on food labels. Just a few weeks ago, The New England Journal of Medicine published a letter by one of our junior colleagues showing that in prepared foods, restaurant foods, and main national chains the amounts of trans fats have been reduced by about 90 percent. There's been a huge change in the last three or four years in the national food supply and probably in everybody's body. If you actually stuck in a needle and analyzed your tissues, you'd find a big difference.

In the field of nutrition, the tools did not exist to answer the most important questions: How does what I eat affect my long term health and well being? The bridge between epidemiology and nutrition provides a way to these answers.