Health in game is a little arbitrary, especially when the game already has vitamins included in its base nutrition system. It seems to be what is sort of considered healthy broadly speaking, like soups and salads.
I don’t believe it considers mutations at all either. For example the positive junkfood mutations won’t protect you from the health effects of scarfing down six bags of potato chips and a pound of caramel.
Health isn’t a super vital thing anyways, it just heals you faster and makes you less likely to catch an ambient disease.