Your cdc should sell fibre 89 and you can add it to your shakes. You can take sennakot to get things moving down there, but then after that your better of taking something regular to prevent it. I take psylium husks tabs every day and i have been fine. You can also get them in a powder form and some people make porridge with them with there shake!! If you do a search you will get loads more info.
I've been taking fiber sure with great success, I was in a terrible state the last time around i nearly jacked it in because of it, but started using it from the start this time and its much better this time around