Same calories and nutrients, but a different response: What ultra-processed foods do to the body

Two meals can contain practically the same calories, proteins, fats, carbohydrates… and even weigh the same. On paper, their impact on the body should be very similar. However, simply changing their degree of processing causes the metabolic response to begin to differ.

This is what a study published on October 5 in Nature Metabolism observed, in which researchers from Virginia Tech directly compared what happens after consuming ultra-processed foods and nutritionally equivalent but less processed alternatives. The results suggest that nutritional composition alone does not explain how our body responds to what we eat.

Two “practically” identical meals

The study was conducted with 57 adults of a considered healthy weight and used a crossover design: participants consumed both an ultra-processed meal and a non-ultra-processed meal at different times, allowing comparison of responses within the same individuals.

The key was how those meals were designed. The researchers adjusted them to be equivalent in energy and components such as carbohydrates, fats, proteins, fiber, sodium, water, and weight. The main difference was the degree of food processing.

After eating, the team analyzed various metabolic indicators to observe how the body used those nutrients. Additionally, they used functional magnetic resonance imaging to later study brain activity while participants viewed images of different foods and rated how much they would be willing to pay for them.

In this way, they were able to observe something that a simple nutritional table would not show.

More insulin and a different use of carbohydrates

After consuming the ultra-processed meal, the insulin response was greater, as was the body's energy response. Furthermore, carbohydrate oxidation was reduced, meaning the use of these nutrients as an immediate energy source decreased.

The result is particularly striking because the meals provided similar amounts of the main nutrients. The observed differences, therefore, could not be explained simply because one had more sugar, more fat, or more calories than the other.

The study suggests that the physical structure a food acquires during processing also influences how its nutrients reach the body and are used after eating.

Processing a food is not just about adding ingredients. Grinding, refining, mixing, or reconstructing its components also modifies its original structure and, with it, the way the digestive system accesses the nutrients.

The researchers believe this different availability could help explain part of the metabolic response found.

The brain also responds differently

The differences were not limited to metabolism. After consuming the meals, the researchers also analyzed brain activity while participants viewed images of different foods.

At a conscious level, they did not rate ultra-processed and non-ultra-processed products significantly differently. However, the MRIs showed differences in activity in several brain regions related to food evaluation, including the striatum, linked to motivation and reward processes.

Moreover, that brain response was related to how each participant had metabolized the meal beforehand.

In other words, although participants said they valued both types of foods similarly, their brains did not respond exactly the same to them.

This does not imply that ultra-processed foods cause addiction or automatically activate reward circuits. The results indicate that the degree of processing is also related to differences in how the brain processes and values signals associated with food.

The nutritional table is not everything

For years, much of the conversation about diet has focused on quantities: calories, sugar, fats, proteins, or fiber. These are fundamental data, but this study reinforces the idea that they alone do not explain how the body responds to a food.

Processing modifies the structure of what we eat and, with it, aspects such as the speed at which nutrients become available or the way the body uses them.

This introduces a variable that is not reflected simply by counting calories or comparing macronutrients. Two nutritionally very similar foods can follow different paths once we eat them.

What this study really contributes

One of the keys to the experiment is precisely having controlled many of the differences that normally exist between foods. In this way, the researchers could focus on processing and observe changes in insulin response, carbohydrate utilization, and certain brain activity patterns.

The trial analyzed what happened during the hours after a meal in 57 adults with a considered healthy weight. The next steps will be to check if those differences persist over time, appear with other types of foods, and reproduce in more diverse populations.

For now, the results add a relevant piece to what we know about ultra-processed foods: their effect does not depend solely on the nutrients they contain. The form the food takes during its preparation also seems to influence how our body responds after consuming it.