It's worth noting that the thing which makes Google so popular is it's result matching.
Their database isn't just "which pages contain which words at which URLs" that's easy -- ignoring size for a moment! -- but the good thing about Google is it cross-matches pages with links to them from somewhere else.
You might have a page without the word "health" in it at all. It might be full of "well-being" and "fitness" and medical words like "viability", but if a million people have linked to it with "here's a good health page", then a search for "health" will have your page at the top anyway.