Known as one of the leading nutrition experts in the U.S., Walter Willett offers tips on how to stay healthy.
Walter Willett
The January 13, 2025 New Yorker article “Still Processing: Why Is the American Diet So Deadly?” described Walter Willett, a professor of Epidemiology and Nutrition at the Harvard Chan School of Public Health, as the expert who “may be the most cited nutrition researcher in the world.”
The article noted that most nutrition scientists blame many unhealthy American conditions such as obesity, diabetes and heart disease on “the American diet including sugary beverages and saturated fats and ultra-processed foods based on its high levels of sodium or cholesterol.” In fact, ultra-processed foods are considered the bane of the American diet and have been linked to “high blood pressure and heart attacks” and may contribute to “cancer, anxiety, dementia and early death.”
In this Q&A, which is lightly edited, Walter Willett offers his nutritional suggestions and insights. He also wrote “Eat, Drink and Be Healthy: The Harvard Medical School Guide to Healthy Eating” and recommends reading the Harvard Chan School of Public Health’s website The Nutrition Source.
Q: That New Yorker article concentrated on the damaging effects of ultra-processed foods on the American diet. Stated simply, what are ultra-processed foods?
Willett: That’s part of the problem. That label is a distraction because there’s a huge amount of unhealthy food on the shelves of our grocery stores and in the American diet. Ultra-processed doesn’t necessarily capture the most important foods that are unhealthy and not all fall into the definition, which can be obscure. It’s a trap because some ultra-processed foods can be healthy like whole grain breads, whole grain breakfast cereals and yogurts.
Q: Which ultra-processed foods stand out?
Willett: If you look at the ones that fall into the category of ultra-processed foods, the most important are sugar-sweetened beverages. That refers to sodas that contain sugar and also fruit drinks like Hawaiian punch. Loads of these fruit drinks may have 5% to 10% real fruit drink, but most contain sugar with artificial coloring. For example, a 20-ounce bottle of Coke consists of about 16 teaspoons of sugar. It causes a surge in blood sugar and in insulin to bring blood sugar down. That leads to excess body weight, which has an adverse metabolic effect.
Q: If a consumer wanted to choose healthier foods and avoid ultra-processed foods, what tips can you offer on how to best achieve that?
Willett: Mostly, choose whole plant foods which would be whole grains, fruits and vegetables. Some greens involve some processing, but they can be cooked and processing is usually minimal. I’d also recommend healthy plant foods, such as nuts, legumes, peanuts, and soy foods. If you want, choose some modest amounts of dairy foods, meats, poultry, fish, which would be a flexitarian diet (a person who follows a primarily vegetarian diet but occasionally consumes meat, poultry or fish).
Q: Would you recommend a Mediterranean diet?
Willett: Yes, and that would consist of lots of vegetables, fruits, grains, and a modest amount of animal sources of protein such as meats and dairy products including fish.
Q: In American restaurant chains, burgers, pizza and tacos predominate. What’s the effect of dining on those foods regularly?
Willett: If you do it occasionally, it would be minimal. If you do it several days a week, the grains and burger buns are refined grains, and the meats are going to be having adverse effects. It’s usually prepared with a large amount of salt. The salt raises your blood pressure, which can lead to strokes and heart diseases.
Q: And many Americans start their day with donuts and pastries. What’s the effect?
Willett: It’s mostly going to be refined grains and sugar, which are bad carbohydrates, and starches that are converted into blood sugar.
Q: So what healthy food would you recommend for breakfast?
Willett: For breakfast, I’d recommend steel-cut oats, some nuts, yogurts and fruits, and orange juice seems to have the healthiest benefit. Apple and grape juices are mostly sugar.
Q: So bottom-line what foods do you recommend?
Willett: Nuts in particular such as peanuts and peanut butter, which happen to be affordable. When I’m rushed, I have for lunch whole grain breads with peanut butter and carrots. It can cost 72 cents and takes 3 minutes to make.
Q: An article on Harvard’s Nutrition Source website recommends “foods high in good fats including vegetable oils such as olive, canola, sunflower, soy and corn, nuts, seeds and fish.” Why these foods?
Willett: First of all, they contain essential fats. We need essential fats. They are part of every cell of our body that make up the majority of our brain and nervous system, and unsaturated fats lower blood cholesterol levels. Those fats are good, and they promote satisfying satiety. You don’t get hungry right away. If you have refined grains, it converts to blood sugar and you’re hungry soon.
Q: So putting this altogether, how specifically do most Americans need to change their diets?
Willett: First of all, being more mindful of what they’re putting in their mouths. Most people do care about their health and what they feed their family. It’s not too hard, and it’s not that complicated, if they focus on emphasizing protein sources but there’s flexibility with dairy.
Q: When they dine out, what should they be thinking of?
Willett: It’s hard to have a healthy meal at most burger and taco places. When dining out, I’d suggest thinking about some of the Asian restaurants like Chinese food. They use healthy fats for stir-frying.
Q: If they want to be healthy and lead a long life, what foods should they be eating?
Willett: It must be something that they enjoy. It can’t be punishment. I grew up in Michigan where the main meal was mashed potatoes, meat and gravy. That’s the standard fifties diet, not a healthy one. That diet leads to heart disease by a rate 4 to 5 times higher.
