hmm... with full disk encryption there is small partition of around 200MB-hmm300MB(?) of size. which is where the boot loader/kernel is stored. other wise whats left to load the OS? some software has to be loaded else how to decrypt and load the system ;)
what can be done is to have the boot partition -as its called- on another drive, like a usb flash drive. that way only encrypted data is on the drive in the computer and you can keep the all important non-encrypted boot partition on a usb drive/sick which you can keep on your person at all times but for when your using/have the laptop booted. so its harder for an attacker to physical get hold of it and add a backdoor. i think this is helpful, when getting though air port "security". so it depends on your threat level or convenience level
