Walter Willett, PhD
Professor of epidemiology and nutrition at Harvard University
What have you learned about how we can protect our health?

Willett: We have collected dietary data on more than 250,000 men and women for a period of 25 years now. What we know is that the major causes of diseases in our country—cancer, cardiovascular disease, stroke, diabetes—are not genetic factors, as so many people believe and use as an excuse, but diet and lifestyle factors. We have documented that unhealthy diet and lifestyle account for more than 80 percent of heart disease, 90 percent of type 2 diabetes, and more than 70 percent of stroke and colon cancer.

Based on your research, what do you recommend people change first?

Willett: It obviously depends on what they are doing at the moment, but at the top of the list: Stop smoking. After that, some combination of increasing physical activity and healthy dietary change.

We ask people to replace unhealthy fats with healthy fats, and unhealthy carbohydrates with healthy forms of carbohydrates—basically eliminate or at least decrease margarines containing trans-fats, commercial deep-fried food, and commercial baked goods. Also, red meat and dairy fat are the major sources of saturated fat—so limiting those is a very good idea.

In terms of carbohydrates: The unhealthy carbohydrates include sugar, which we consume as a nation in huge amounts in soda, beverages, snacks, desserts, and refined starches. Some people focus on removing only sugar, which is a mistake because refined starches (like white bread, white rice, white pasta) behave almost identically to sugar metabolically, and they also contain very low amounts of nutrients and low amounts of fiber. If we replace those with whole grain, high-fiber carbohydrates, which include brown rice, whole grain bread, oatmeal, and less familiar kinds of carbohydrates such as barley and quinoa, then you win twice because you are getting rid of something bad and replacing it with something that has health benefits.