Inactive Ingredients: Aspartame, Dibasic Calcium Phosphate, FD&C Yellow 6, Malic Acid, Maltodextrin, Orange Flavor (Natural, Artificial), Potassium Citrate, Riboflavin
Any kind of artifical flavor is going to affect insulin response/blood sugar...so if your purpose of a fast is to not have an insulin response...then yes it would technically break the fast. And how something with "maltodextrin" is sugar free?? Ummmm....someone is taking liberties with the "serving size"...as if it is under 0.5grams then the FDA says you can list it as 0grams...so yes anything can be sugar free if you get the "serving size" small enough.
Also on the whole "You need fiber" standard line docs hand out along with "fat is bad for you".....read these...and pass along to your doc
Comes down to if you are eating fruits and vegetables, and avoiding processed foods and other bad substitutions (like sausage, hot dogs, etc...), you don't need extra fiber as you will get enough. That and avoid bran like the plague, it's an anti-nutrient. If you want to do a fiber load to clear out the system for a week....feel free as a little gut housecleaning is always good (do water, flaxseeds grounded, some acv or probiotics...your own personal Colon Blow...personally wanting to try some Bentonite clay as I hear that pulls all sorts of "stuff" out). But there is no real proof that high fiber actually reduces any kind of prostate cancer (which is why your Dr recommends it). Eat right foods in the first place, get enzymes to break it all down and you don't need all the other things as it is digested properly and the body will get rid of the waste....funny how it all comes full circle...healthy meat, vegetables, some fruit, healthy fats.....all you need.