We prepared, portioned, and provided all meals and snacks for the study. Both diets emphasized minimally processed ingredients

I was initially concerned the results could possibly explained simply by calorie restriction. However in the full paper they have a mechanism which does well to address this.

Participants were not instructed to intentionally restrict caloric intake; instead, they were allowed to request additional study foods when they needed, without any limits.

Full paper here

I would have liked to have seen if any participants actually did request more though indicating they understood the option, but I recognize the limits of the study for trying to control this one variable.