In general, placing any sufficiently constraining restriction on what you eat will cause weight loss, just because it interferes with caloric intake.

Pretty interesting study design. The weakness of nutrition studies is almost always that they're either observational in nature or heavily confounded by factors that can't be controlled for.

In this case, the trial was interventional and they randomized participants into two groups with a crossover design. You either spent 8 weeks on the ultra-processed diet, followed by a 4-week washout in which you ate whatever you wanted, then spent 8 weeks on the minimally-processed diet, or you did that but in reverse with MPF first and UPF second. In both cases, participants were provided meals and drinks, at 4000 KCal a day, and told to eat as much or as little of it as they wanted, but they had to only eat and drink what they were provided, except water.

That gets rid of a lot of objections typically made regarding studies like this. The results mean nothing to me personally, but I'm glad to see nutrition science at least making some advances in methodology to clean up data reliability.