BIG include file !!!

Hey Guys, I am developing an application in PHP. I make use of an include file that contains regularly used functions. As I am working I am taking more and more of the code out and putting it into functions straight into the include file. This file is included on almost every page and I am worried that it is going to slow the pages down. Will it have a large effect on the pages speed. It's only about 400 lines at the moment but getting bigger the way I am working Is it likely to slow the pages much even if only some of the functions are called from particular pages. Thanks, Abe