I think it's significant that in both of your papers the experiment is performed with 0-calorie snacks as the alternative to processed foods. Personally I think it's kind of a "no duh" experiment (a snack with no calories has no energy to impart), but scientists still gotta do science to prove science.

I confess I haven't read any of the papers myself, but there is a growing body of research that points to health risks from processed foods. And when you look at the ultra-processed food that's cheap and readily available, you're going to find stuff that's loaded with sugar, palm oil, and who knows what kind of additives. The vast majority of those foods are also low fibre which isn't great either.

Nutrition is both highly complex and really simple. It's complicated because there's a lot of systems at play within your body, and it can be difficult to definitively assess the benefits or risks of certain ingredients. But it's simple too because we all know that eating good food is good for you, and eating bad food is bad for you.

I do think it's excessive not letting the kids eat the snacks their parents give them. The administration will never know how food secure people are (a lot aren't), and the children are especially vulnerable because they don't have the autonomy to tell a teacher to fuck off. But at the same time, everyone knows it's better for your kid to eat carrots than pop tarts.