What happens in your body after you eat something may depend on more than the nutrients listed on the label. Even when two meals contain nearly identical amounts of calories, carbohydrates, fat, protein, water and salt, how processed the food is can influence both metabolism and brain activity, a new study suggests.

Fifty-seven adults of a healthy weight and aged 18 to 45 took part in a study by researchers at Virginia Tech's Freylin Biomedical Research Institute. Participants were given two nutritionally matched 300-calorie meals on separate visits, with at least three days between sessions. The participants served as their own controls, allowing researchers to compare their responses to minimally processed and ultraprocessed foods.

The findings add another piece to a complicated nutritional puzzle: two foods can look remarkably similar on a nutrition label yet prompt the body and brain to respond differently.

Of the 57 participants, 32 completed both the metabolic and brain-imaging sessions, providing the researchers with data linking bodily responses to neural activity in the same people. The researchers carefully matched the meals to within one percent for calories, carbohydrates, fat, protein, water and salt.

The ultraprocessed meal included small portions of a peanut butter and jelly sandwich, deli turkey, vegetable chips, a cookie, cereal and instant mashed potatoes. The minimally processed meal included banana, dried cranberries, cheese and egg.

After fasting overnight, participants entered a sealed metabolic chamber, where researchers measured their energy expenditure and metabolism. They then had 10 minutes to eat one of the meals. Researchers drew blood immediately afterward and six additional times during the following three hours, measuring changes in insulin, blood sugar, energy expenditure and carbohydrate oxidation.

When they ate an ultraprocessed meal, participants' bodies expended more energy and burned fewer carbohydrates for fuel.

The results surprised investigators. "We were shocked when every single metabolic metric differed,” the study's first author, Zach Hutelin, a researcher at the Fralin Biomedical Research Institute and a doctoral researcher in Virginia Tech's Translational Biology, Medicine and Health (TBMH) graduate program, said in a press release.

The ultraprocessed meal prompted the body to expend more energy and burn less carbohydrate for fuel than the minimally processed meal, despite their nearly identical nutritional profiles.

The next question was whether these metabolic differences were reflected in the brain.

Thirty-two of the participants in the study underwent functional MRI scans on a separate visit while viewing pictures of minimally processed and ultraprocessed foods. They rated how much they would be willing to pay for each food, allowing researchers to compare subjective food value with activity in brain regions involved in motivation or reward.

The participants did not report that they valued one type of food more than the other. However, differences in carbohydrate oxidation after the meals were associated with differences in activity in the striatum, including the ventral striatum and caudate areas involved in reward, motivation and learning.

The study does not prove that ultraprocessed foods cause diabetes, obesity or other diseases, nor does it establish which aspect of processing produced the metabolic changes. The participants were young and healthy, the experiment examined only one pair of meals, and the protein sources and additives differed between meals. And researchers did not fully measure the physical and chemical structure of the foods.

For now, the findings add another piece to a complicated nutritional puzzle: two foods can look remarkably similar on a nutrition label yet prompt the body and brain to respond differently. And that distinction is a whole other nutritional story to chew on.

The study is published in Nature Metabolism.