yes I would recommend you take some form of fiber this diet is great but it can play havoc with the toilet works I was at my wits end with it around weeks 3 and 4 even though I was going every day it was just very difficult and adding the fiber can really make things so much easier
have a look at this thread. you can buy them loosley and add them to shakes, some people make porridge and you can get them in tablet form aswell. hth becky x