There has been a paradigm shift in recent years about how we think of ultra-processed foods in our diets. Photo / 123rf
Former National Institutes of Health researcher Kevin Hall says you can find healthy choices even among ultra-processed foods.
A decade ago, most people had never heard of ultra-processed foods.
But that changed in 2019, when Kevin Hall, then a scientist at the National Institutes of Health, published a study that shocked the nutrition world.
Hall recruited a group of healthy adults and put them on two different diets. One diet consisted of mostly homemade, unprocessed foods like fresh fruits and vegetables, nuts, whole grains, Greek yoghurt and salads with grilled chicken. The other contained an assortment of packaged foods: sugary breakfast cereals, blueberry muffins, canned ravioli, chocolate milk, goldfish crackers, potato chips and other staples of an ultra-processed diet.
Hall found that the participants consumed an extra 500 calories a day on the ultra-processed diet and quickly gained weight – even though both diets were matched for nutrients such as salt, sugar, fat and fibre.
The study created a paradigm shift in how we think about nutrition, prompting public health experts to realise that it’s not just the amount of salt, sugar, fat and calories in our food that matters for our health, but also the extent to which our food undergoes industrial processing.
Hall resigned from the NIH earlier this year after alleging that the Trump administration was censoring him, a claim that the administration has denied. But Hall’s work has had a lasting impact. Health and Human Services Secretary Robert F. Kennedy jnr has called ultra-processed foods a core driver of chronic disease, and countries around the world have issued dietary guidelines urging people to avoid eating them.
Now Hall has written a new book, Food Intelligence: The Science of How Food Both Nourishes and Harms Us. In the book, Hall and his co-author, journalist Julia Belluz, uncover how our modern food environment drives us to overeat, while also exploring and debunking widely held beliefs about metabolism, nutrition and obesity.
I spoke to Hall about what makes ultra-processed foods so easy to overconsume, whether some are less harmful than others, and which – if any – ultra-processed foods he includes in his diet. This interview has been edited for length and clarity.
Q: What’s something that many people get wrong about the obesity and Type 2 diabetes epidemic?
People still have this idea that there’s a lack of personal responsibility that has pervaded society. A lot of people argue that declines in physical activity may have played a role. But while that may be true for some people, there isn’t really much evidence that any of these two factors have played a major role in the spread of obesity and Type 2 diabetes. Unless we had this massive loss of willpower across the population that was only manifested in terms of food then this can’t be a real explanation for what’s going on. If you look at the data we have on physical activity, you’ll see that work-related physical activity has gone down, but leisure-time physical activity has actually gone up.
There’s this perception that if we could just get people to take more control over their lives and improve their lifestyles then we could reverse the tide of obesity and diabetes. I’m sure many individuals have had success doing those things – and more power to them. But to expect that that’s going to be the driver of major changes at the population level is a little too much to hope for.
Q: Do you think that the major driver of obesity and diabetes is what we’re eating?
A: Not just our food but the overall food environment. That’s one thing we have to be careful about. Our food environment is not just about our food – it’s the marketing of food, it’s how convenient and cheap and tasty it is. I think that’s a natural progression of this desire we’ve had to adequately feed the growing population. Decades ago, we were worried about mass starvation, so we put in place policies and incentives to mass produce protein and calories at an industrial scale, and that’s created a calorie glut.
In the book, we calculated how many calories per person per day are grown in the major food commodity crops in the United States – that’s wheat, soy, corn and rice. Just in the US, we grow 15,000 calories per person per day. And the food system is designed to get rid of those calories. We feed a huge chunk of them to animals primarily for factory farming. We find ways to create biofuels out of corn and soy. And then we’ve come up with really ingenious ways in food technology and food science to create cheap inputs for ultra-processed foods.
One of the much-talked-about inputs these days is high-fructose corn syrup. We use corn to create a sweetener that didn’t exist before the middle of the 20th century, and it’s now become the major calorie-container sweetener in ultra-processed foods.
Q: In one of your landmark studies, you found that people consume an extra 500 calories a day when they’re eating ultra-processed foods compared to when they’re eating mostly unprocessed foods. What was most striking to you about the findings?
A: Ultra-processed foods are really heavily marketed: they’re cheap. They’re sold in relatively larger portion sizes, and they’re convenient. In our study, we eliminated all those things. People didn’t have to buy them or prepare them, and they didn’t know what brands they were.
Our question was: is there something about ultra-processed foods themselves that causes us to eat excess calories and gain weight – even after you match the amount of calories and macronutrients in them to a diet of minimally processed foods? And the answer was yes. There is something about these foods that causes them to have this property.
Q: And what do you think that is?
We went back and did some post hoc analyses to figure out what attributes of the meals were associated with increased calorie intake. Two things popped out. I think probably the most important one is that the ultra-processed foods tended to be higher in energy density – that’s calories per gram or calories per bite. It’s because the food matrix is disrupted, and the foods have been dried out. That’s done on purpose during the processing of these foods because extracting moisture from them preserves their shelf life. It prevents bacterial growth. But when you remove a lot of the water you also concentrate the calories.
Another thing we found is that the ultra-processed foods were hyper-palatable. Foods are considered hyper-palatable when they have specific combinations of fat and salt, fat and sugar, or carbs and salt. Hyper-palatable foods tend to be higher in these pairs of nutrients.
The participants also ate the ultra-processed foods more quickly, suggesting that maybe by the time their guts had signalled to their brains that they were full it was already too late.
Q: You did a follow-up study digging further into this. What did you find?
In our most recent study, we reformulated the ultra-processed diets so they would vary in the amount of energy-dense and hyper-palatable foods they contained. We had a diet of minimally processed foods, and we had diets where 80% of the calories were from ultra-processed foods. But we wanted to see what would happen if we lowered the overall energy density of the meals and decreased the amounts of hyper-palatable foods on the ultra-processed diets.
We’re still analysing the data and writing up the results. But we presented the results of an interim analysis back in November, and it looked like people did not overconsume calories on a highly ultra-processed diet if both energy density and the proportion of hyper-palatable foods were matched to the minimally processed diet. So it seems like we’re getting toward mechanisms.
That kind of information is going to be useful when we make recommendations to policymakers and food makers.
Q: I have to ask: Do you eat ultra-processed foods?
A: I do. I eat some of the bad ones – the tasty treats – but I treat them as recreational substances. I also eat ultra-processed foods that from a nutritional perspective are pretty good even though they contain certain additives. I use, for example, a marinara sauce that’s low in sugar and sodium, but when I’m making a nice pasta dish it cuts down the preparation time. I’m not going to make a marinara sauce from scratch. Just because something is ultra-processed doesn’t necessarily mean it’s bad for you.
Q: What do you eat in a typical day?
I’m not a breakfast eater, so breakfast is usually just coffee. And lunch is often leftovers from the night before. I’ll usually have a piece of fruit or some nuts or hard-boiled eggs before lunch, usually around 11:30am or so. Then I’ll have lunch around 1pm. For dinner, marinara sauce plays a pretty prominent role. I might get some frozen scallops and some whole-wheat pasta, and grill up some veggies. Those are common things in our household, at least for the adults. For our kids, we’ll try to include some things that we know they like. They’ll eat green beans and salmon, but they’re very particular. They like farmed Atlantic salmon. When we eat scallops, they’ll eat veggies and rice and beans, but they’ll also have things that we won’t eat, like chicken nuggets. It can be a little challenging, but we make it work for the whole family.
Q: What – if any – diet advice do you have for people who want to eat healthy?
At this point, from what we know about nutrition science, it really does come down to the boring old diet advice. You should be eating more fruits, vegetables and whole grains, and avoiding saturated fat, sugar, salt and refined carbs. You can fit a lot of diets into that. You can do low-carb based on that. You can do low-fat on that. It cuts across many cultures. You can adapt many different diets to that advice.
We shouldn’t get too caught up on the current bogeyman, which is ultra-processed foods. You can find healthy choices even in the ultra-processed foods category.