I have looked at that site a couple times, and when I apply my limited knowledge much of this information is off base. Realize , for other readers, that I studied animal science, which is primarily the feeding of livestock, and have raised sheep and horses for some 30 years.

I cant see how 6 cups of vegies a day causes a problem. I suspect if there is a problem, it is caused by lack of the right microbes to break down the fibers. ALso I tend to have more issues (constipation) with an all meat diet than a mixed diet. Otherwise, as I remember, too much ground flax, or too much bran, would cause constipation too. My takeaway is that a small amount of grd flax or bran seems to be ok, and lots of fiber both soluble and insoluble contained within whole foods is the way to go.

And as with livestock, small changes to the diet over a 2 week transition would be prudent. Just like with livestock.