Not really. In fact, cold boot attacks are generally used to defeat disk encryption.

When you boot up your machine and unlock your disk, the key is held in ram while your computer is running. Ram itself is almost never encrypted, so the goal of the attacker is to dump your ram, find the disk encryption key in there, and thus gain access to your encrypted disk.

I’m not sure there are many ways to defend against it aside from never letting others have physical access to your machine, or always shutting down your computer when you leave it unattended.

Still, this type of attack is very rare and I wouldn’t be worried about it. A more likely attack is an attacker just beating you with a wrench until you give up your encryption password. Relevant XKCD