Do you assume that if two foods have the same calories and the same amounts of protein, fat and carbohydrates, they will affect your body the same way?
Checking calories and nutrition facts is an important part of eating well. However, new research suggests that even foods with nearly identical nutritional content may trigger different responses in the body and brain depending on how heavily they are processed.
On October 5, 2026, the international journal Nature Metabolism published a randomized controlled study comparing ultra-processed foods with minimally processed foods.
The study analyzed post-meal insulin secretion, energy metabolism and brain activity when viewing food in 57 healthy adults.
In this article, we explain what the study revealed about the link between food processing and health.
What Are Ultra-Processed Foods, and How Do They Differ from Ordinary Processed Foods?
Ultra-processed foods (UPF) are foods made through industrial manufacturing processes that contain ingredients and additives not typically used in home cooking.
The NOVA classification, a system for grading how processed foods are, divides foods into four groups according to their degree of processing.
Ultra-processed foods include snack foods, packaged sweet breads and pastries, some instant foods and soft drinks.
On the other hand, frozen vegetables and foods that have undergone only simple processing are not necessarily classified as ultra-processed.
Previous research has reported that people who eat more ultra-processed foods tend to have a higher risk of obesity, metabolic disorders and cardiovascular disease.
However, it had not been fully understood whether this was due to differences in the sugar, fat and calories in these foods, or whether processing itself played a role.
So this study matched calories and key nutrients as closely as possible to examine the differences caused by the degree of food processing.
A New Study That Matched Calories and Nutrients
The study, published on October 5, 2026, involved 57 adults at a healthy weight.
The participants’ average age was about 26, and 32 of them took part in a test of post-meal metabolic responses.
The research team prepared meals of about 300 kcal each, one using ultra-processed foods and one using minimally processed foods.
The two meals were adjusted to match not only in energy but also in protein, fat, carbohydrates, fiber, salt and water content.
The researchers also matched, as closely as possible, an indicator of how quickly each meal raises blood sugar.
Participants ate both meals on separate days and underwent blood tests and energy metabolism measurements for about three hours after eating.
This is a research method called a “crossover trial,” in which the same people experience each of the different conditions.
This approach allowed the researchers to compare the effects of food processing while minimizing the influence of individual differences.
What makes this study distinctive is that it examined whether the body responds differently even when differences in nutritional content are removed as much as possible.
Ultra-Processed Foods Led to Differences in Insulin Secretion and Energy Metabolism
Among the results, the blood sugar and insulin responses drew particular attention.
When post-meal blood sugar was compared over the whole measurement period, there was no statistically clear difference between the two meals.
Insulin secretion, however, was a different story.
After eating the ultra-processed meal, post-meal insulin secretion increased significantly compared with the minimally processed meal.
In particular, between 40 and 120 minutes after the meal, insulin levels were higher in the ultra-processed condition.
Insulin is an important hormone that regulates blood sugar, for example by helping cells take in sugar from the blood.
These results suggest that even when blood sugar changes are almost the same, the body’s response in regulating it may differ.
Differences were also found in post-meal energy expenditure and in the proportion of carbohydrates and fat used for energy.
With the ultra-processed meal, the post-meal energy expenditure response was larger, while the use of carbohydrates for energy was relatively smaller.
However, these are short-term metabolic changes, and these results alone cannot be used to judge insulin resistance or the development of diabetes.
Even so, the study produced an intriguing result: even when calories and nutrients are nearly the same, the way the body processes food can differ.
Can Food Processing Even Change How the Brain Responds?
This study examined not only the body’s metabolic responses but also the brain’s responses to food.
In 52 participants, the researchers used functional MRI (fMRI) to measure brain activity while participants viewed pictures of food.
Participants were shown 28 food photos in total: 14 ultra-processed foods and 14 minimally processed foods.
They were also asked to rate how much money they would be willing to pay for each food.
The results showed no clear difference by degree of processing in how much participants were willing to pay.
But a closer look at brain activity revealed differences in how the brain responded when evaluating the value of food.
In particular, different patterns of activity depending on the degree of processing were seen in the striatum, which is involved in the reward value of food, and in brain regions that process visual information.
In addition, individual differences in post-meal carbohydrate metabolism were linked to how the brain responded to the food photos.
This suggests that the body’s response after eating a food may be related to how the brain processes information about food.
When we choose what to eat, it is thought that not only taste and smell but also how our bodies responded to a food in the past play a role.
However, what this study measured was brain activity while looking at photos.
It did not prove that eating ultra-processed foods always increases appetite or harms the brain.
Still, the finding that the degree of food processing is linked to brain responses that nutritional content alone cannot explain is a notable discovery.
What Should We Keep in Mind for a Healthy Diet?
This study suggests that calories and nutritional content alone may not be enough when considering how foods affect our health.
Processing changes the shape and structure of foods.
For example, finely grinding ingredients or repeatedly heating and shaping them may change how they are digested and how their nutrients are used.
The research team suggests that these differences in the physical structure of foods may be related to the body’s metabolic responses and to the signals sent to the brain.
However, this was a short-term experiment involving a relatively small number of healthy young adults.
Also, although the nutritional content was nearly the same, there were differences in factors such as protein sources and food additives, so it cannot be concluded that the degree of processing alone produced the results.
For this reason, we cannot conclude from these results that eating ultra-processed foods will inevitably cause weight gain or illness.
Nor does it mean that all processed foods are bad for your health.
In daily life, it is important to make use of the convenience of processed foods while also including a good balance of minimally processed foods, such as vegetables, fruit, beans, fish and whole grains.
When thinking about a healthy diet, looking not only at “what and how much we eat” but also at “how our food is processed” may offer a new perspective.
Rather than focusing only on numbers like calories and nutrients, let’s choose our daily meals with an eye to the nature of the ingredients themselves.