Degree of food processing affects metabolism and brain function

The experiment involved healthy adults aged between 18 and 45. The main part of the study included 57 participants, of whom 32 underwent both metabolic tests and brain scans using functional MRI. Each participant tried both lunch options on different days (with a gap of at least three days) so that the response of the same person to different degrees of food processing could be compared.

To ensure the purity of the experiment, the scientists selected two dishes, each containing 300 kilocalories, that were as similar as possible in terms of composition: the difference in proteins, fats, carbohydrates, water, and salt did not exceed 1 %. The NOVA scale, which classifies foods according to the level of industrial processing, was used as a reference point.

The highly processed option included a piece of a sandwich with peanut butter and jam, a slice of deli‑style turkey, vegetable chips, cookies, cereal, instant mashed potatoes, and a small amount of water. The minimally processed set consisted of sliced banana, dried cranberries, cheese, and an egg. According to the label, these dishes would look almost like twins, but their effects on the body turned out to be quite different.

To measure the metabolic effects, participants came to the laboratory after an overnight fast and were placed in a sealed metabolic chamber — a special room where the energy expenditure and metabolic characteristics could be accurately assessed. After the baseline measurements, they were given 10 minutes to eat one of the dishes. Then, blood samples were taken immediately after the meal and six more times over the next three hours.

The results surprised even the researchers themselves, as literally every measured metabolic indicator differed. When consuming highly processed food, the body released significantly more insulin, blood sugar levels remained slightly higher for a little longer, and carbohydrates were used as an energy source less actively. At the same time, the body expended more energy overall. Chronically elevated blood glucose levels are a risk factor for developing diabetes and other metabolic disorders, so even short‑term differences can have long‑term consequences.

Experts have obtained no less interesting data by studying the work of the brain. On a separate day, the participants looked at photos of the same products (and others, but also matched in nutritional composition) and said how much they would be willing to pay for each item. At that time, they underwent fMRI scans to track how blood flow changes in different areas of the brain, and hence their activity.

The researchers paid special attention to the ventral striatum and the nucleus accumbens, areas associated with motivation, learning, and the reward system. It turned out that the differences in how the participants burned carbohydrates after each type of food correlated with how their brains reacted to images of food. At the same time, the participants themselves did not state that they were willing to pay more for highly processed foods, but their brains suggested otherwise. The influence of food processing on behavior may be unconscious and operate at the level of neurophysiology.

“We wanted to find out: if all the key nutritional parameters are artificially fixed, will the food processing itself have any independent effect on the result?” explains Alex DiFeliceantonio, associate professor at the Fralin Institute for Biomedical Research at the VTC and head of the laboratory that conducted the study. The answer was yes.

It was noted that studying not only metabolism, but also brain activity is a valuable contribution, because it is the brain that ultimately regulates eating behavior.

It is worth considering the limitations of the study. It considered only one pair of 300-calorie dishes, and the participants were young and healthy. In addition, although the amount of protein in the dishes was the same, its sources varied, and the highly processed version had more additives. The scientists also measured the total fiber content, but did not analyze the physical and chemical structure of the products, which can affect the rate of absorption of nutrients.

The authors plan further research, they want to study the influence of various factors, for example, specific additives or individual processing steps, on metabolic reactions, as well as expand the sample to include other population groups, larger portions and a greater variety of food pairs.

Against the background of these data, statistics are particularly revealing: highly processed foods account for more than half of the average daily caloric intake of an ordinary American, and diets around the world are increasingly shifting towards such foods. It is specially made convenient, affordable, inexpensive and as attractive as possible to taste, so it is easy to overeat it. Previously, the association of such products with obesity, cardiovascular diseases, type 2 diabetes, and even some mental health indicators was primarily explained by their composition (high in fat and sugar, low in fiber and protein), but now there is increasing evidence that the processing technology itself also plays an independent role.

It turns out that the way the food was produced can imperceptibly affect both the metabolism and the motivation to eat more than necessary. It is these mechanisms that are now becoming a new point for scientific research and, possibly, future nutrition recommendations.