Ultraprocessed meals alter metabolism and brain response even when nutrients match

What the study found

A team at Virginia Tech's Fralin Biomedical Research Institute at VTC has published evidence in Nature Metabolism that food processing itself changes how the body and brain respond to a meal, even when the nutritional content is essentially identical.

According to Virginia Tech's news service, the researchers served healthy adults two 300-calorie meals that were matched within 1 percent on calories, carbohydrates, fats, proteins, water and salt. One meal was minimally processed, the other highly processed. Despite the nutritional equivalence, the ultraprocessed meal triggered a higher insulin response, kept blood sugar somewhat elevated for longer, increased energy expenditure and shifted the body away from burning carbohydrate as fuel.

First author Zach Hutelin, who conducted the work as part of his doctoral research, described the team's surprise that every metabolic measure they tracked came out different between the two meals.

How the experiment worked

The study recruited 57 healthy adults aged 18 to 45, of whom 32 completed both the metabolic testing and the brain-imaging sessions. Each participant ate both meal types in separate sessions spaced at least three days apart, allowing the researchers to compare how the same person reacted to each.

Participants arrived after an overnight fast and entered a metabolic chamber — a sealed room used to measure energy expenditure — where baseline readings were taken. They then had ten minutes to eat one of the two meals, selected using the Nova classification system, which groups foods by degree of industrial processing. The highly processed meal included items such as a peanut butter and jelly sandwich bite, deli turkey, veggie chips, a cookie, cereal and instant mashed potatoes; the minimally processed meal consisted of sliced banana, dried cranberries, cheese and egg. Hutelin noted that the two meals would look practically identical on a nutrition label.

Blood was drawn immediately after eating and six more times over the following three hours to measure insulin response, energy expenditure and carbohydrate oxidation.

The brain's reward system responded too

On a separate day, participants viewed pictures of nutritionally matched processed and unprocessed foods while undergoing functional MRI, and reported how much they would be willing to pay for each item. Activity in the ventral striatum and nucleus accumbens — regions tied to motivation and reward — varied in ways linked to how participants burned carbohydrates after each type of meal. Participants did not assign higher subjective value to either category of food, but the imaging suggested that metabolic differences from processing correspond to differences in how the brain reacts to food cues.

Carlos A. Monteiro of the University of São Paulo, the epidemiologist whose work produced the Nova classification, told Nature Metabolism that a key open question is whether ultraprocessed foods' link to poor health stems from their nutrient makeup or from the processing itself. He called the team's addition of brain measurements a novel and important contribution, since the brain ultimately governs eating behavior.

Known limitations

The study examined a single pair of matched 300-calorie meals in young, healthy adults, and the researchers acknowledge constraints. Protein sources differed between the meals and could have influenced results, and the ultraprocessed meal contained more additives. The study measured total fiber but did not analyse the physical and chemical structure of the foods. Principal investigator Alex DiFeliceantonio said the group next wants to test other populations, longer time periods, larger meals, more food pairings, and to isolate specific factors such as commercial additives or particular processing steps. Funding came from the National Institutes of Health and a National Science Foundation graduate research fellowship.

Why it matters

Ultraprocessed foods account for more than half of the average American's daily calories, and diets worldwide are shifting toward them. Population-level data already associate heavy consumption with obesity, cardiac events, Type 2 diabetes and some measures of mental health, but the mechanism has been unclear. If processing alone — independent of calories, macronutrients and salt — produces distinct metabolic and neural responses, the standard assumption that nutritionally equivalent meals are interchangeable breaks down. That reframes both how nutrition studies should be designed and how regulators and food makers might think about labeling and reformulation.

For a technically minded audience, the study is also a useful case study in experimental control: by holding nutrition constant within 1 percent and measuring within-subject responses in a sealed metabolic chamber, the researchers turned a vague correlation between processing and disease into a specific, measurable physiological effect — one that now points toward additive composition and food structure as the variables worth interrogating next.