You’ve probably heard of ultra-processed foods before, and if you have, you probably know that they’re not the healthiest foods you can eat.
These industrially manufactured foods are increasingly associated with increased risk of disease, and research suggests they can affect the way we think and harm our mental health.
In light of all the worrying associations scientists have discovered, it’s easy to assume that ultra-processed foods are unhealthy because they’re filled with nutritionally poor ingredients — but what if there’s more to it than that?
“We know that the majority of ultra-processed foods are high in fat, sugar, fiber and protein,” says neuroscientist Alex DiFeliceantonio of Virginia Tech.
“But if we artificially hold all these things constant, is there something in the treatment that leads to a different outcome?”
It appears the answer is yes, according to a surprising discovery reported in Natural metabolism.
In their study, DiFeliceantonio and his team recruited 57 healthy-weight adults, with an average age of 26. Among them, 32 people participated in a food experiment in which they ate two separate meals on two different days, in random order.
One of the meals consisted of ultra-processed foods, including deli turkey, instant mashed potatoes, a chocolate chip cookie, frozen wheat cereal, vegetable chips, a small sandwich consisting of white bread with peanut butter and jelly, and a small serving of water.
The other meal consisted of minimally processed foods, including a hard-boiled egg, a banana, cranberries, cheese and sea salt.
Most interestingly, these two meals – although very different on the plate – were largely nutritionally identical, being identical in terms of nutritional composition and energy (300 calories each).
“Both meals contain 1 percent carbohydrate, fat, protein, calories, water and salt,” says Zach Hutelin, a biomedical researcher at Virginia Tech and first author of the study.
“If these meals had a nutrition label, they would be virtually identical.”
Although their nutritional labels may have been the same, the metabolic responses they triggered turned out to be very different.
A series of blood samples taken over the three hours after each meal showed that blood sugar responses were generally similar for the two meals, although blood sugar remained elevated longer after the ultra-processed meal.
The contrast in insulin response was more marked, with insulin levels increasing significantly more after the ultra-processed meal and remaining higher for about two hours, before both meals returned to near baseline levels after three hours.
The ultra-processed meal triggered a higher metabolic rate and greater fat burning during the three-hour observation window, but less carbohydrate burning than the minimally processed foods.
“We were shocked to find that each metabolic measurement differed,” says Hutelin.
“What we noticed with ultra-processed foods was that the insulin response was much higher and the blood sugar stayed a little higher for a little longer.”
Although we don’t know for sure why the metabolic responses were so different, the research offers some clues.
In a separate experiment, participants viewed images of ultra-processed and non-ultra-processed foods while having their brain activity monitored using functional MRI.
For participants who also took part in the eating phase of the experiment, brain activity showed an association between neuronal activity in the striatum (a part of the brain involved in reward systems) and how well they burned carbohydrates during the eating session.
Researchers suggest this could mean that the way our bodies burn food for fuel is linked to specific signals about the foods we eat – and, possibly, how processed they are.
“Collectively, our results support the hypothesis that food processing may influence metabolic responses and reward processing through mechanisms beyond caloric content and macronutrient composition,” the researchers explain in a briefing on their study.
“These mechanisms could involve altered nutrient availability due to altered physical structure in ultra-processed foods.”
Another possibility is that commercial food additives incorporated into ultra-processed foods could affect our metabolic response when we eat them, which the researchers intend to examine next.
The results are reported in Natural metabolism.
This article was fact-checked by Rebecca Dyer and edited by Rebecca Dyer. Although we are proud of our process, we are only human. If you spot an error, please let us know.
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