When writing about different topics it is difficult enough to come up with unique content without worrying about how your page title may effect who you reach.
The fact is that no matter what you title your page you may find the same content may attract people differently and search engines may not use the title when ranking returns for searches.
It is relatively easy to prove to … if you search for something on a major search engine there is a good possibility the pages returned will not have page titles related to the search but this does not mean the content about the search is not available on the linked pages.
So when naming your pages it is best to write for humans.
If you are writing a page about pizza then say that in the title this way people that do find your page from a search engine will understand the content on the returned link is related to what they are searching for.
How much information should you include in your title?
This depends on who you are trying to reach… for the most part your titles should be descriptive and include a keyword or two related to the content but you will find that even database generated titles with only 1 or 3 words can return as many clicks as very descriptive titles.
Again write your page titles for humans to read.
Keywords and page titles
You should use keywords when appropriate but not specifically to attract SEO rank improvement.
Again use your best judgment here.