function nameOfFunction($query) {
if ($query->is_feed) {
$query->set('cat','-1');
}
return $query;
}
add_filter('pre_get_posts','nameOfFunction');

Note : the -1 is the category id, I didnt try it but I suppose you could change the category parameters where it says cat to something like category_name and still get the same result.

You could also just change the is_feed to some of the other conditional tags that WordPress has for a different effect.

Thanks to Lucas for suggesting I share this!

He built a site for a local South African band called the Brothers Streep and it got featured on a british talk show called the Graham Norton Show. Reason it got featured is that the band wrote a song about Anna Paquin and the show had her on and played the song to her!! Great stuff…also awesome for Hugh as the site was shown on live TV
Check out the video: