Health and Medicine
PUBLISHED
Knowing what to eat can be pretty tough these days. Despite being surrounded by more varieties of food than at any point in human history, mounting evidence has raised substantial questions about many modern food products, especially ultra-processed foods (UPFs).
These vaguely defined foods have been linked to multiple negative health outcomes, including potential associations with cancer, heart disease, organ damage, advanced aging, and even poorer mental health.
But why do they potentially cause harm? Although UPFs have become a mainstay of concern in the public sphere, the mechanisms underpinning their effects on our bodies are unclear.
One of the reasons why UPFs may be less healthy for us is that they often contain nutritionally poor ingredients, but new research suggests there may be more going on. In particular, the results indicate that food processing may affect how our bodies and, significantly, our brains respond to food that goes beyond its nutritional components.
“We know that the majority of ultra-processed foods are high in fat, they're high in sugar, they're low in fiber, and they're low in protein,” Alex DiFeliceantonio, a Virginia Tech associate professor at the Fralin Biomedical Research Institute, explained in a statement.
“But if we artificially hold all of those things constant, is there something about the processing that leads to a different outcome?”
To investigate this, DiFeliceantonio and colleagues recruited a small cohort of 57 healthy adults from the university and surrounding area. Thirty-two of the participants, all between 18 and 45 years of age, took part in an experiment where they ate two separate meals – referred to as metabolic sessions – on separate days.
The UPF meal consisted of small peanut butter and jelly sandwich, slices of deli turkey, veggie chips, a cookie, cereal, instant mashed potatoes, and a little bit of water. In contrast, the minimally processed meal included sliced banana, dried cranberries, cheese, and egg.
These meals were selected using the Nova scale, which categorizes foods in four groups based on their level of processing.
Nova categories “go through ‘unprocessed’ or ‘minimally processed’ foods – these are things like, you know, fresh fruit, possibly frozen fruit, meat, those sorts of things. Then you've got ‘culinary ingredients’, which is really like sugar and salt,” senior specialist dietician Duane Mellor previously explained to IFLScience.
“Then you have ‘processed foods’, which is basically the act of anything that's been prepared using standard ingredients. And then ‘ultra processed’ is where it's prepared in an industrial scale, possibly with ingredients which wouldn't normally be used in a traditional kitchen environment.”
Each meal had 300 nutritionally matched calories. “The two meals are matched within 1 percent of carbs, fat, proteins, calories, water, and salt,” Zach Hutelin, another researcher at the institute added. “If these meals had a nutritional label, they would be practically identical.”
To examine the metabolic effects of these meals, participants fasted overnight before arriving at the testing site. They then got onto a twin-sized bed in a metabolic chamber – a sealed, airtight space designed to measure human energy expenditure and metabolism. This allowed researchers to take baseline measurements.
After an hour, the participants were given 10 minutes to eat one of the meals that were randomly assigned to them. The researchers extracted blood immediately after the meal and then six subsequent times over the next three hours. They then measure post-meal metabolism, including insulin response, energy expenditure, and carbohydrate oxidation.
“We were shocked when every single metabolic metric differed,” Hutelin said. “What we noticed with the ultra-processed food is that insulin response was much higher and blood sugar stays a little bit higher for a little bit longer.”
This is a worrying result, especially as chronically elevated blood sugar increases the chances of conditions like type 2 diabetes.
The researchers are not sure why the metabolic responses differed to such an extent, but a second experiment may help fill in some of the gaps. This experiment moved away from the metabolic responses to food and focused in on the neurological responses.
To assess this, participants viewed pictures of UPFs and minimally processed foods – they were still nutritionally matched – while having their brains scanned by functional MRI. These scans measured brain activity by tracking changes in blood flow across different regions of the brain.
While viewing the food, participants reported how much they would pay for it, allowing the team to compare how participants valued the food and how their brains responded. They observed notable results in the regions of the brain involved in learning, motivation, and reward (the ventral striatum and nucleus accumbens).
In particular, differences in how participants’ brains responded to pictures of the food were linked to how they burned carbohydrates for energy after each meal. Participants didn’t say they were willing to pay more for ultra-processed or minimally process foods, but it seems that metabolic differences produced by food processing are associated with how the brain respond to food cues.
The study is published in Nature Metabolism.
