Most nutrition experts believe that two meals with the same calories, carbs, fat, and protein will affect blood sugar in much the same way. A new study challenges that idea. It suggests that how much a food has been processed may matter, even when the nutrition label looks identical.
Highly processed foods have become a major part of modern diets, accounting for over half of the calories consumed by the average American. Their popularity is growing worldwide, driven by their affordability, convenience, and appealing flavours. However, these same qualities can make it harder for people to control how much they eat.
Studies of large groups have linked heavy consumption of these foods to obesity, heart problems, type 2 diabetes, and even some mental health issues. But scientists have not been sure why. Most ultraprocessed foods are high in sugar and fat and low in fiber and protein. So it was difficult to tell whether the problem was the nutrients or the processing itself. A team at the Fralin Biomedical Research Institute, part of Virginia Tech, set out to test the hypothesis. Their results appeared in the journal Nature Metabolism.
The researchers began with 57 healthy adults aged 18 to 45. Of these, 32 finished both the metabolic tests and the brain scans. Each person tried both kinds of meals on different days, at least three days apart. This let the team compare each person with themselves.
The two meals each contained 300 calories. They were matched very closely on carbs, fat, protein, water, salt, and weight, usually within one percent. The team used the Nova scale, which sorts foods into four groups based on how much industrial processing they go through.
The less processed meal consisted of banana slices, dried cranberries, cheese and egg. In contrast, the highly processed meal included small portions of a peanut butter and jelly sandwich and deli turkey, alongside vegetable chips, a cookie, cereal, instant mashed potatoes and a small amount of water.
Participants fasted overnight and then rested in a metabolic chamber. This is a sealed room that measures how much energy the body uses. They had ten minutes to eat. Afterward, the team took blood samples right away and six more times over three hours.
The results surprised the team. The two meals affected the body in different ways. After eating the ultraprocessed meal, the body produced more insulin, and blood sugar levels remained slightly higher for longer. Although the body used more energy, it relied less on carbohydrates for fuel.
Over time, high blood sugar can raise the risk of diabetes. As the study’s first author put it, the meals would look practically identical on a nutrition label. Yet the body treated them differently.
The lead scientist studies why people choose the foods they do. So the team also looked at the brain. On a separate day, participants looked at pictures of both types of food while inside an fMRI scanner. This scan tracks blood flow to show which brain areas are active. Participants also said how much they would pay for each food.
The team focused on a brain area linked to motivation, learning, and reward. People whose bodies burnt carbs differently after the two meals also showed different brain responses to the food pictures. Yet participants did not say they would pay more for one type of food. Therefore, the link appears to operate independently of conscious choice. An outside expert who helped create the Nova system called the work important. He noted that the brain ultimately controls eating behaviour.
The researchers are careful about what the results mean. The study tested only one pair of 300-calorie meals. The participants were young and healthy. The protein came from different sources in each meal, which could have affected the results. The ultraprocessed meal also had more additives. The team did not measure the physical structure of the foods.
The scientists want to test other groups of people, larger meals, longer times, and more food pairings. They also want to find out which specific factors cause the effects. These could include additives or particular processing steps.
For now, the study offers a useful clue. The way food is made could also shape how our bodies and brains respond to it. The research was funded by the National Institutes of Health and the National Science Foundation.
