Conditionals – Single Post in Specific category

I want to change sub links to my main navigation depending on what category a user if viewing a single entry from. So, say I have an entry in a category called “reviews”. I want all the single posts in the reviews category to show the different subnav for those pages.

I’ve tried to use the is_category/is_single conditionals, but the is_category just shows the nav on the category archive page.

I know I could create a new template for those categories I want to have different navigations, but I was wondering if it’s possible using the conditionals to tell it if this post is in this category than this is the subnav that should display.

I hope I didn’t over-explain that.

Lindsey