Same menu on paper, 500 extra calories in practice
Researchers matched two diets for calories, sugar, fat, and fiber down to the gram, and one group still ate far more.
In 2019, NIH researcher Kevin Hall put twenty adults in a metabolic ward for a month and fed them two diets in turn: one built from ultra-processed foods, one from minimally processed foods like oats and grilled chicken. Both were engineered to match on calories, sugar, fat, sodium, and fiber. Subjects could eat as much or as little as they wanted.
On the ultra-processed diet, people ate about 500 more calories a day and gained close to two pounds over two weeks. On the whole-food diet, without being told to diet, they lost roughly the same amount. Protein intake barely moved either way; the extra calories came almost entirely from carbohydrate and fat, eaten at a measurably faster pace per meal.
Because this was a randomized trial, not an observational survey, it's the first evidence that processing level itself, not just nutrition-label content, can cause overeating.
The formula on the package was identical both weeks. The plate wasn't.