Kevin Hall likes to eat red lentil pasta and a tomato sauce that contains some preservatives to preserve the red color, both products that he calls ultra-processed. But, he says: “Those are not the ultra-processed foods what you should be concerned about. If you look at the nutritional value, they look fine. You don’t eat too much of it easily.”
The American nutritional scientist, a physicist by training, has spent decades researching diabetes and obesity. Few researchers could do what Hall did: put groups of people in the lab for weeks and turn their entire metabolism inside out to find out the effect of, for example, fat and carbohydrates in our diet, or ultra-processed food.
The Dutch translation of his book will be published this week Food Intelligencein which he met The New York Timesjournalist Julia Belluz tries to answer the question why we eat what we eat in 480 pages.
What have all those years of research into carbs, fat and UPFs actually taught you?
“Especially that the body adapts surprisingly well. You can interchange carbohydrates and fat in the diet in large quantities, and yet the effects are minimal on how many calories you burn and how much fat is stored in your body. That ingenious system often goes out of the picture when people talk about carbohydrates and fat. But it makes little difference to your weight whether you low carb or low fat eats, we saw in the lab.
“So the question was: what determines that some people maintain their weight more easily than others? What type of diet and what eating patterns make obesity so prevalent? It turned out that people in an environment with a lot of ultra-processed food consume on average 500 kilocalories more per day than people who were served hardly processed meals. And now we want to better understand how the food environment influences our appetite and our weight.”
Kevin Hall.
Photo The New York Times
You devoted an entire chapter to protein. About the glorification of protein as the ‘one true nutrient’. Why so much attention?
“I was amazed that the way many people now talk about protein-rich foods and supplements can be traced back to the ideas of Justus von Liebig [de Duitse chemicus die als de uitvinder van kunstmest wordt gezien]. From being a renowned chemist, he emerged as a diet guru who earned a lot of money at the end of the nineteenth century by selling meat extracts. He had all kinds of intriguing hypotheses about protein that turned out to be largely wrong, but are still going around.
“Many people think that they should eat more protein than they actually do, while most people already consume more than their body needs. As people get older, or if they want to grow muscle, the optimal amount may be slightly higher, but people often forget that the effect of extra protein is small compared to the strength training you need to do to become more muscular.”
Less protein prolongs life in mice. We just don’t know yet how that translates to people
Above a certain level, you write, protein no longer does anything for you, and can even be harmful.
“A classic fact in biology is the trade-off between reproduction (reproduction, cell growth) and lifespan. In animals we see that they can reproduce better with a higher protein intake, but live shorter. Less protein prolongs life in mice. We just don’t know yet how that translates to humans. One question, for example, is: does this apply to all protein or are there specific amino acids that you should look at?”
What remains clear from your research is that ultra-processed food is by definition unhealthy. In what ways have your conclusions been misunderstood?
“On the one hand, there is the idea that we attribute a mysterious mechanism to ultra-processed meals, just because they have that qualification. In addition, there is a group of people who are not really interested in how it works, but are attacking the food industry with our research. I think you have to understand the mechanisms to understand why people in countries like the United States get so many calories from ultra-processed food. Only then can the government take measures against certain products and force manufacturers to reduce their salt, fat and sugar content.” stop.”
What do we actually know? Is it the taste that is so irresistible? Or is it the processing at the factory that makes UPFs unhealthy?
“You talk about taste, but in our studies people say they like unprocessed and highly processed meals just as much. We use the term hyper-palatability for the combinations of so much sugar, salt and fat, or so many carbohydrates and salt, that they do not occur in nature.” In the book, Hall writes: that could also be your grandmother’s apple pie, or the cheese sauce on your broccoli. “That hyper-palatable food may have effects outside our awareness. It may trigger signals in our gastrointestinal tract that regulate our appetite.
“Texture is another characteristic: many of these products are easy to chew away. Due to industrial processing, the physical structure has been broken down in such a way that nutrients are absorbed much earlier in the digestive tract. But that does not explain everything. Energy density is also an interesting one, and it is certainly related to the degree of processing: water is removed from the food for shelf life. The concentration means that there are relatively many calories in one bite.”
Halfway through your book you suddenly write: let’s not put too much emphasis on biology. It’s the environment! Why then so much attention to metabolism, hormones, and how hunger and cravings work in the body?
“There is an interaction between the tempting food we are surrounded by and fundamental processes in the body. My hypothesis is that it has to do with signals from the gastrointestinal tract to the reward center in the brain.” Just seeing something tasty, or knowing that you are going to eat soon, can activate the release of dopamine, Hall describes. That can encourage you to eat, which gives a new dopamine peak that makes you continue to eat. That urge can sometimes be stronger than the signals your brain receives that your stomach is already full.
Yet you do not conclude that food is addictive.
“We looked in the brain to see whether milkshakes cause dopamine peaks comparable to the dopamine explosions you see with nicotine or cocaine. But that turned out not to be the case. It was striking that people with obesity had a higher baseline level of dopamine, while the assumption was that these people have fewer dopamine receptors. I am not saying that food cannot be addictive, but it is too simplistic to say that dopamine peaks hijack the brain. We don’t know.”
Influencers make all kinds of strong claims based on very little science to sell their product
The wellness industry takes a beating in your book. ‘Imprecision nutrition’ is what you call the hype of glucose meters and personalized nutrition programs.
“Influencers make all kinds of strong claims based on very little science to sell their product. But ‘if it doesn’t help, it doesn’t hurt’ is certainly not the case. For example, my co-author Julia had high cholesterol because she was advised to eat more fat. Glucose meters are also very unreliable, they all give different results. If you are now afraid to eat a banana because it would cause a blood sugar peak, that does not make your life better. Trust in nutritional research, that is already under pressure, does not benefit from the false promises of this kind of pseudoscience.”
The Make America Healthy Again movement, led by Secretary of Health Robert F. Kennedy, seized on your research as proof that ultra-processed foods are bad and addictive. But the movement eventually turned against you.
“It is true that under the current administration there is more attention to the science behind ultra-processed food, but only if the results suit them. They think they know what they need to know, and anything that does not fit with that is downplayed. When we wanted to publish our results from our milkshake experiment, people appointed by the Trump administration at the National Institutes of Health withheld the press release. An interview request from a journalist was denied because the results did not match the views of RFK. Then another article, which had already been accepted for publication, was censored because it was also about ‘health equity’, and we were no longer allowed to use that word. Ultimately, I closed down the lab where I worked for 21 years and ‘retired’.”
You are now working on obesity drugs for AstraZeneca. How is that?
“The entire industry is busy with safe, effective medicines, but little is invested in research into eating behavior. We see that people eat less when they start taking GLP-1 medication. I think it is crucial to investigate how these medicines change eating behavior and the quality of the diet in the long term. The food industry should also want to know that, even more so big pharma.”
In this industry and with these medications, don’t you feel like you are treating the symptoms?
“No. I see obesity as the result of an agricultural system that produces too many calories. The problem is no longer that we cannot feed the world’s population, but that that population is ‘overfed’. I think medicines can help people who are most susceptible to this. This is a unique period in history: we will soon have to feed almost ten billion people properly, without fueling diseases and burning up the earth. What we have to do now is to land this plane softly, and all passengers go home healthy to bring.”
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