slow mysql database

[Torsten Mueller]

Hi,
i have a data base wich will have 500000 lines.
At the moment it have 190000 lines and it's so very slow...
Here is the structure:
CREATE TABLE `produkte` (
`nummer` int(11) NOT NULL AUTO_INCREMENT,
`anbieter` text NOT NULL,
`ueberschrift` text NOT NULL,
`beschreibung` text NOT NULL,
`bildlink` text NOT NULL,
`shoplink` text NOT NULL,
`preis` float NOT NULL,
`marke` text NOT NULL,
`kat1` text NOT NULL,
`kat2` text NOT NULL,
`kat3` text NOT NULL,
`kat4` text NOT NULL,
PRIMARY KEY (`nummer`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=193560 ;

I have to search the kat elements. So i made the following PHP order:

$sql="SELECT distinct kat4 FROM produkte WHERE kat1='".$_SESSION['kat1']."' AND kat2='".$_SESSION['kat2']."' AND kat3='".$_SESSION['kat3']."'";
$res=mysql_query($sql) or die(mysql_error());
if(mysql_num_rows($res)!=0){
$sql="SELECT distinct kat4 FROM produkte WHERE kat1='".$_SESSION['kat1']."' AND kat2='".$_SESSION['kat2']."' AND kat3='".$_SESSION['kat3']."'";
$res=mysql_query($sql) or die(mysql_error());
...
And here i fill the option element in a while loop.

This i make for 4 select elements.
So the script needs more than 12 seconds. It's to slow.
How can i make it's faster?

Thanx for help.

Best regards.
Torsten