Thought for food: Walter Willett on diet for personal and planetary health

The global nutrition leader reflects on the controversies of his career – and the benefits they continue to bring

Willett's recommended diet embodied in a meal of vegetables (cauliflower), seeds and plant oils. Courtesy of Caravan
17 September 2019

Walter Willett will speak at the Global Landscapes Forum New York on 28 September 2019. Learn how to join the event here.

In 2000, Walter Willett toppled the U.S. Department of Agriculture (USDA) food pyramid. The triangular diagram – showing the recommended portion size of each food group – had been hung in classrooms, grocery stores and homes all over the U.S. and beyond since it was released in 1992.

But Willett’s decades of research had proven it wrong, and so he rebuilt it. Exercise and weight control formed his bottom-tier foundation rather than bread and pasta; red meat, butter and refined grains were brought up to the top alongside salt and sweets. Certain fats were highly recommended throughout, staring down the low-fat fad of the time with scientific evidence.

His breakout research, which began shaping his pyramid and paving his way to become one of the world’s five most-cited scientists, was leading the second phase of the Nurses’ Health Study (NHS), which illuminated groundbreaking correlations between diet and disease. First created in 1976, the study’s questionnaire has since been continually developed by Willett and other doctors and scientists, documenting the food and lifestyle habits of more than 200,000 men and women.

Today, the NHS stands as one of the most comprehensive health studies ever conducted. The findings of its third phase, specially focused on the later-life effects of adolescent diet and dietary links to breast cancer, are still to come.

From his desk at the Harvard School of Public Health, where he is now a professor after serving more than 25 years as chair of the school’s nutrition department, Willett still knows how to make a splash. He has penned novels like 2011’s bestselling Eat, Drink, and Be Healthy and been the face of headline-making reports like last year’s EAT-Lancet, which outlined the complete overhaul of the food system needed to feed a projected world population of 10 billion in 2050 without destroying the planet in the process.

Here, he tells Landscape News about his career – and its inadvertent controversies, which continue to make the world healthier for all.

Courtesy of Walter Willett
Courtesy of Walter Willett

In the early stages of your career, little research had yet been done about the links between diet and disease. What made you curious to start researching this topic? 

One of the reasons that little research had been done was that many leaders in nutrition thought they knew the answers (e.g., avoid eggs and fat in general), but when I looked for the evidence, I realized there was very little. I was working as an internal medicine physician at that time and was mostly caring for people with conditions I couldn’t cure, such as diabetes, heart disease and many cancers. I wanted to learn what caused these conditions and how to prevent them. For this reason, I went back to school to get a degree in epidemiology and then connected this with nutrition.

You spent time living in Tanzania during medical school. What did that experience teach you about diet and food systems?

My work in Tanzania impressed me with the powerful effect of our environment on health and disease. Mainly, I was dealing with issues of poor sanitation and environmentally-related diseases like malaria. Coronary heart disease, on the other hand, was almost nonexistent. 

The NHS rose you to academic fame. How did you develop the design of the questionnaires used in that study, which you still use in various forms today? 

Before going to Tanzania, I used a simple food frequency questionnaire while in medical school to conduct a survey in the Potawatomi Native American community in the upper peninsula of Michigan. I was impressed that we could gather much information that way. In my doctoral degree program at Harvard, I worked on an analysis of smoking and heart disease in the NHS and realized that this could be an ideal population in which we could collect dietary data, because the participants were already being followed for incidence of cancers and cardiovascular diseases. 

Through a series of pilot studies, I identified about 60 foods that were the major contributors to intake of the key nutrients in which we were interested, and then administered the questionnaire to the 121,000 women in the main study. By using optical scanning methods [to input data via scanning systems], we were able to double the size of the questionnaire and continue updating it to align with food supply and diet trends every four years.

Most importantly, we have conducted a series of validation studies comparing our standardized questionnaires with detailed weighed diet records and biomarkers and have documented sufficient validity to provide informative data on diet and long-term health. Of course, any assessment of diet will never be perfect, and we have also developed statistical methods to take measurement errors into account.

The USDA food pyramid published in 1992. Kelly Garbato, Flickr
The USDA food pyramid published in 1992. Kelly Garbato, Flickr
Walter Willett's food pyramid published in 2000. Courtesy of Harvard Health Publishing
Walter Willett’s food pyramid published in 2000. Courtesy of Harvard Health Publishing

When you were researching fats, it was evident that your findings would be controversial. Were you scared to make a splash with your research?

Yes, I knew our findings would be controversial. When we published our early results, it was believed that all fats were bad, and there was nothing different about trans fat. Through the NHS, we found that women who had the most trans fats in their diets had a 50 percent higher chance of developing coronary heart disease. I didn’t feel scared about publishing the results but knew that there would be pushback. Having been quite involved in anti-war efforts during the Vietnam War era was good preparation.  

How do the links between climate change and diet affect your research and recommendations? 

I have been aware that our dietary choices can affect greenhouse gas production and climate change for quite a while. What has changed is the realization that climate change is greatly accelerating. Several decades ago, it appeared that these changes would be seen over several hundred years. However, the rapidity of change has made this an urgent issue, so I’ve been spending more time on this, working with earth science colleagues. This has made it possible to look simultaneously at both the human and planetary health impacts of different dietary scenarios. 

The report from the EAT-Lancet Commission, which you co-chair, received global attention when it was published last year. How did that feel? 

We hoped it would get attention, so that was good. Of course we knew there would be backlash from the beef folks. Some of that is helpful, as it increases attention. The recommendations were made to be global. The dietary targets include ranges, and there is also much flexibility because of the opportunities for substitutions, so this is readily adaptable to many different cultures and food supplies. 

What are some of the biggest mysteries you still want to solve? 

Some of the greatest questions about diet and health are related to the ends of the life cycle. For example, how does adolescent diet affect our health later in life?  We are starting to get some answers to this. One enigma is that being lean as a child is a strong risk factor for breast cancer for the rest of a woman’s life, and we don’t know why.

And at the other end, we still need to understand more about how diet can help preserve cognitive function. 

In general, diet and lifestyle factors that prevent cardiovascular disease will help reduce cognitive decline. However, we are seeing evidence that some specific fruits and vegetables can be particularly important, and we are actively working on learning more. I am optimistic that dietary factors can play an important role in delaying cognitive decline.   


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