In a one-of-a-kind study published in the journal Cell Metabolism a group of researchers has shown that a diet based on ultra-processed foods leads to safe weight gain, as opposed to diets which, despite having the same dosage of fat and sugar, do not include processed foods.
The experiment involved 20 healthy adult subjects divided into two groups: one adopted a diet based on unprocessed foods such as fruit, vegetables and nuts for two weeks, the other had bread, sausages and other processed foods.
Both diets had the same amount of calories, macronutrients, sugars, sodium and fiber.
“I am surprised by the evidence that emerged in this study,” explains Kevin Hall, one of the authors, “because I thought that by providing the same amount of fats, proteins and carbohydrates there would be no appreciable difference between the two diets”.
After two weeks of testing, the ultra-processed food group gained an average of 1kg of body weight while absorbing around 500 extra calories each day. Previous studies attributed the cause of weight gain to sugars, fats and salts contained in processed foods, but this research changes the perspective: there is a mechanism not yet explained at the basis of this difference.
The “structural” hypotheses
“The sensory properties or density of processed food itself could lead people to eat it more quickly: this means that our gastrointestinal tract does not have enough time to signal the sensation of fullness to the brain”
The blood samples taken from each group also show other elements: in subjects who have ingested unprocessed foods there is an increase in the PYY hormone, a natural appetite suppressant.
Some doubts
The biggest limitation to the very interesting study is in the distinction made between ultra-processed and unprocessed foods: there is no official categorization in all respects. Gunter Kuhnle, a nutrition expert from the University of Reading, believes that the definition of “processed food” has become a generic category used to describe all “toxic” food, when often processing foods is important and necessary for their preservation and their palatability.
“According to the NOVA classification, used by the authors of the study, the cooling and packaging of foods makes them already processed. Butter and cheese are therefore "processed" foods. The definition of "ultra-processed" is completely arbitrary."
Gunter Kuhnle, University of Reading
The researchers of this study, however, take these early categorization difficulties into account, and announce that they want to improve the distribution of foods in the diets that will be administered in subsequent studies.
“We need to know what aspects of ultra-processed foods change people's habits and calorie absorption that lead to weight gain,” Hall says. “The next study will be carried out with reformulated diets in order to make the components of foods that could play a greater role in this mechanism clearer and more identifiable”.
