Comment by gorgoiler

Enriched flour is another good example that I was hoping someone would mention*.

It’s worth noting that it’s also slightly different in that processed flour is deficient in thiamin and calcium, so the fortification adds back these nutrients.

On the other hand, processing water to make it potable doesn’t remove fluoride and so fluoridation is not the process of adding back something that was there beforehand.

*I searched this page and found flouride and flouridation four times before your comment.