A groundbreaking study shows that people eating ultra-processed foods consume more calories and gain weight compared to those on minimally processed diets—even when both provide identical calories and macronutrients.
This is the first randomized controlled trial to test ultra-processed foods under the NOVA classification, which flags items with industrial additives like hydrogenated oils, high-fructose corn syrup, flavorings, and emulsifiers.
Earlier observational studies linked processed food-heavy diets to health risks, but lacked randomization to prove causation—leaving questions about whether lifestyle factors or food access played a role.
“Although we examined a small group, the results of this tightly controlled experiment showed a clear and consistent difference between the two diets,” said the study's lead author. “This is the first study to show causality—that ultra-processed foods cause people to eat too many calories and gain weight.”
The trial involved 20 healthy adults (10 men, 10 women) living in a facility for a month, randomly assigned to ultra-processed or minimally processed meals for two weeks each. Examples: Ultra-processed breakfast was a bagel with cream cheese and turkey bacon; the minimally processed version was oatmeal with bananas, walnuts, and skim milk. Meals matched in calories, sugars, fiber, fat, and carbs—participants ate freely.
On the ultra-processed diet, they ate about 500 more calories daily, faster, and gained an average 0.9 kg (2 lbs); on the unprocessed diet, they lost the same amount.
