First, the researchers have to fund their work, which can take years. Then the work has to be vetted and approved by an Institutional Review Board, which safeguards subjects from potential harm. I.R.B.s are especially vigilant when studies involve children, a vulnerable group. Even if the research is of minimal risk, this process can take months.

Then there’s getting permission from schools to do the work. As you can imagine, many are resistant to allowing research on their premises. Often, protocols and rules require getting permission from parents to allow their children to be part of studies. If parents (understandably) refuse, figuring out how to do the work without involving some children can be tricky.

Finally, many methodological decisions come into play. Let’s imagine that we want to do a simple test of cookies versus apples, plus or minus stickers — as this study did. It’s possible that children eat different things on different days, so we need to make sure that we test them on multiple days of the week. It’s possible that they might change their behavior once, but then go back to their old ways, so we need to test responses over time.

It’s possible that handing out the cookie or apple personally might change behavior more than just leaving the choices out for display. If that’s the case, we need to stay hidden and observe unobtrusively. This matters because in the real world it’s probably not feasible to have someone handing out these foods in schools, and we need the methods to mirror what will most likely happen later. It’s also possible that the choices might differ based on whether children can take both the apple and the cookie (in which case they could get the sticker and the treat) or whether they had to choose one.

I point out all these things to reinforce that this type of research isn’t as simple as many might initially think. Without addressing these questions, and more, the work may be flawed or not easily generalized.

These difficulties are some of the reasons so much research on food and nutrition is done with animals, like mice. We don’t need to worry as much about I.R.B.s or getting a school on board. We don’t have to worry about mice noticing who’s recording data. And we can control what they’re offered to eat, every meal of every day. But the same things that make animal studies so much easier to perform also make them much less meaningful. Human eating and nutrition are typically more complex than anything a mouse would encounter.