So I have surgery scheduled for 12/2/14. I have been on my pre-op diet (low fat, sugar, carb) since 11/10/14. I am doing really well and am averaging between 7-20 grams of fat a day. Well in the last week I have noticed I am not able to go to the bathroom hardly ever. There is a lot more effort involved on my part to do so if you know what I mean. Well today I finally got some movement and the toilet was full of blood.. any idea if this is serious or not?

I think it is urgently serious and you need medical attention immediately.  Hopefully it is only fissures from straining but still get to an emergency room.

You probably have developed a hemmoroid from constipation or passing hard stools. Have it checked in the ER. If you see that amount of blood again it could be serious.

A little bit of blood looks like a lot in a toilet. If you are not actively bleeding, then I don't think you need to go to the ER, and more than likely it was caused by a fissure (cut). Best wishes.

"...full of blood...." is pretty serious.  You could just have a slight fissure from straining, but you might want to talk to your PCP anyway.  

To avoid straining, use Miralax or stool softeners.

If it was bright red and stopped when you had finished, I wouldn't worry.   Low fat can have a constipating effect and straining can cause a fissure or haemorroid both of which are painful and bloody.  

Consider Miralax, stool softeners or Magnesium to keep you regular and soft to allow whatever you have to heal and try not to let it get to the point where you have to strain again!

did you eat beets?

They can make the toile****er red when passing through..