Take a moment and think about the scientific systems you learned about in school. Cellular structures, organ systems, chemical names and reactions, electrical systems, types of foods—they're all just arbitrary. We call some chemicals "phenols" and others "alkanes" because they have different structures that make them react certain ways. We say that some things are fruits and others are vegetables and still others are nuts or legumes (and we can argue forever about where tomatoes fall in that spectrum) but at the end of the day it's still just a categorization system that we came up with because it's useful to talk about food in those terms. And if it's not useful, we should change the system.