On top of the lending sub you can find the stickies everyone should read first.
https://bitcointalk.org/index.php?topic=577765.0The rule of "No Collateral, No Loan" means that in order to get a loan you must give collateral that is equal, or preferably higher to the amount you are being loaned.
If you completely ignore this sticky and make a loan request with no collateral, without having massive trust on the forum, the chances of you getting negative trusted feedback and therefore having a Trade with Extreme Caution tag is almost 100%.
So yes, collateral always is mandatory.