In 2019, nutrition scientist Kevin Hall and his colleagues published eye-popping results from a unique experiment. For four weeks, study participants stayed in a hospital ward at the National Institutes of Health, splitting their time on two different diets: one high in minimally processed foods, the other high in ultra-processed foods, products that contain factory-made ingredients and additives not found in a typical home kitchen. On the ultra-processed diet, individuals ate a whopping 500 calories more per day.
Although small and time-limited, this was the first experimental study to link UPFs to human obesity. The work has since been cited in hundreds of scientific papers and continues to garner attention from the news media. The research was also featured in a bestselling book by Chris van Tulleken, “Ultra-processed People: The Science Behind Food That Isn’t Food.”
It might come as a surprise, then, that Hall has teamed up with award-winning health journalist Julia Belluz for a new book that takes a nuanced approach to UPFs: “It’s not a manifesto of demonizing ultra-processed foods,” he told Undark. Instead, the authors chart a fascinating history of nutrition research, showing how time and again, preliminary discoveries get swept up in fad diets or packaged into commercial products of dubious benefit. “We’ve rarely been humble in our application of nutrition science,” they write.
When it comes to ultra-processed foods, they argue, it’s important to study all of their properties to better understand which, specifically, cause people to overeat.
Hall recently left his longtime position at the National Institutes of Health, citing censorship under the new health secretary, Robert F. Kennedy Jr. (The NIH has disputed this charge.) Even before then, Hall ran into headwinds: The government agency initially balked at the prospect of a book that waded into the diet wars and food policy, said Hall, noting that the NIH’s mission is to generate science. He ultimately hired a lawyer and the NIH “allowed me to write it as an outside activity,” Hall said. On her end, Belluz received a grant from the Alfred P. Sloan Foundation. (Belluz is also a former fellow of the Knight Science Journalism Program, which publishes Undark.) The end result is “Food Intelligence: The Science of How Food Both Nourishes and Harms Us.”
Our interview was conducted by Zoom and edited for length and clarity.
Undark: “Food Intelligence” criticizes the diet industry for focusing on two common questions: “What’s the best diet?” and “How can I lose weight?” What’s wrong with these questions, and what should we be asking?
Kevin Hall: There’s nothing wrong with those questions in principle. What we’re trying to point out is that by focusing on the individual, making recommendations at that level, and having competing diet factions seemingly constantly at war with each other — it’s all been a big distraction.
People get extremely confused because they’re being told very conflicting pieces of evidence that have a kernel of truth to them but have been extrapolated well beyond what the scientific basis is. What we’re missing is the fact that our food environment has changed dramatically in the past 50 years, which makes it extraordinarily difficult for people to choose healthy diets that belong to any of these different competing factions.
We’re being marketed to, and we’re getting bombarded with the opportunities to eat exactly the opposite kinds of foods that don’t match any of those kinds of diets — those are the foods that are the most convenient, and the most affordable, and that most easily fit into our lifestyles.
Julia Belluz: It’s not that people can’t succeed on these different diets. We tried to highlight that in the book. From an all-potato diet to an all-meat diet, humans can adapt to this absolutely incredible variety of eating patterns and not only survive but thrive. But going back to this focus on individual choices: The massive effects Kevin and others have found in studies happen when you change food environments. We knew this from animal experiments where you feed rats supermarket diets [consisting of junk food], and suddenly you can induce levels of obesity you never saw with just trying to feed them standard or even high-fat chow.
It’s also sad that so many — and I was one of them — so many people walk around just feeling like they’ve failed. We’re trying to shift the focus to the fact that it’s not the individuals who have failed. It’s the policymakers. It’s our leaders who have failed to protect us from these toxic environments.
UD: There’s an interesting tension in your book, which is that on the one hand, you’re calling for policy changes. And on the other hand, the book really emphasizes some of the scientific uncertainty underlying a lot of nutrition research.
KH: There is an interesting tension because we do know a lot about what makes a healthy diet. And as we just mentioned, there are a variety of different dietary patterns that can fall within that. We know that diets in general that have lots of non-starchy vegetables, whole grains, legumes and are low in added sugars, saturated fats, and sodium are generally healthful diets. The issue is that we don’t have access to those kinds of foods.
What we do have access to is a food environment — currently, in the U.S., Canada, the U.K. and many other places — that’s dominated by ultra-processed foods. Chris van Tulleken’s book does an excellent job trying to better understand what the problems with many ultra-processed foods are. What I think people might miss from that narrative is that ultra-processed foods often lack the basic characteristics of healthy foods: UPFs tend to be low in fruits and vegetables and legumes and whole grains. And they tend to be high in salt, saturated fat, and added sugars and low in fiber.
[But] the mere fact that a food is ultra-processed does not necessarily make it unhealthy. And, in fact, part of the path forward is to better understand: What is it about ultra-processed foods that makes them unhealthy? What is it that’s part of our ultra-processed food environment that’s driving over-consumption of calories?
If we can better understand that, then we can target our policies more towards making ultra-processed foods that are healthy for us. The ultra-processing part is what makes them convenient, and makes them affordable, and makes them mass-produced for a large chunk of the population, which is what we need to do because we can’t expect everybody to create freshly cooked meals from their backyard gardens. That’s not going to be the solution to our problems moving forward.
JB: And this uncertainty in the science. We were trying to point to lots of uncertainty in some of these nonsense solutions people put forward, like continuous glucose monitors for healthy people, or whatever the idea du jour is. But this foundational knowledge that researchers have worked really hard to win: What does a healthy diet look like? Even though it’s boring at this point, I don’t think anyone quibbles with these broad ideas, as Kevin said, about it’s a diet that’s low in sodium; it’s a diet that’s low in saturated fat; it’s a diet that’s low in added sugar; it’s a diet that has lots of fresh fruits and vegetables.
Kevin Hall is a nutrition and metabolism scientist who worked at the NIH for more than two decades.
Visual: Courtesy of Kevin Hall
Julia Belluz is a health journalist and contributing opinion writer for The New York Times.
Visual: Katarina Lindbichler
UD: Can you give an example of a healthy meal that might include an ultra-processed food?
KH: So, I’m not talking about making healthy Twinkies. I’m not talking about making healthy Fruit Loops. I’m talking about, how do you use food technology and food science to make the things that we know constitute part of a healthy diet more convenient, more readily available, and more accessible to more people?
One example that we use in the book is pizza. It is a huge part of the American diet. It’s one of the most popular foods in the country, and it’s relatively unhealthy, the way that most of us use our pizza. The dough is high in refined carbohydrates, smothered in cheese with lots of saturated fat, and it has a huge amount of sodium and even added sugar in the tomato sauce. We highlight the work of some colleagues in the U.K. who basically redesigned pizza from the ground up to still make it really tasty and convenient, but to meet all of the nutritional targets for the U.K. Eatwell Guide. There was even a study, published in PLOS One, trying to estimate the population impact of improving pizza quality in the U.S. Because we eat so much of it, [a reformulation] could actually have a meaningful effect on public health.
JB: I went into the book a little bit skeptical. Like, really, are ultra-processed foods part of the answer? I grew up with the food movement and this idea that we just need to cook our own meals, and this is the way out of it. For many people, that is a great answer. It’s wonderful on the precautionary basis if you can reduce your consumption of ultra-processed foods. But for most people, that isn’t going to be the answer.
The eye-opening piece was just all the data we have on how you put grocery stores or fresh food markets in food deserts — it doesn’t move the needle. It’s because people don’t have the time. They don’t have, in some cases, the knowledge. They don’t have the access to the resources that you need to cook in a way that eliminates ultra-processed foods and the convenience they’ve given a lot of people over many decades.
KH: We’re only at the beginning stages of understanding what it is about ultra-processed foods that tends to cause poor health. But the point is that those are answerable questions [given] enough investment in research. That’s some of the research I was doing at the NIH before I left.
We also need to know what not to target. What are the things that are parts of ultra-processed foods that are perfectly fine for you and can be still incorporated as part of healthy products? I don’t want to give the impression that it’s just a no-brainer. We actually do need to invest in the science.
JB: One of the questions we asked in a survey we commissioned for the book was, “Which would you say is stopping you from eating a healthier diet?” And among the top answers were, I live in a household where healthy diet is not a habit. It’s just not part of the culture in the household. I rely on prepared food because it’s hard for me to find healthy prepared food near me. I don’t have the time to cook. I don’t enjoy healthy food options. The taste, how it makes me feel.
Those were among the top answers. It’s a little bit more complicated than just saying we all need to just cook our meals from scratch and return to the kitchen or whatever it is.
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