There has been a lot of research on this. The problem is, the results have been conflicting with one study showing benefit and protection against cancer and other ailments and others showing no benefit, at least with regards to protection against colon cancer.
I agree that it's very difficult to separate the benefits of pure fiber from the vitamins, minerals and phytonutrients that foods with high amounts of fiber also contain, so we are still left with the question: is it the fiber or something else?
Grains are known to cause problems for a variety of people in the form of gluten allergies, IBS, Rheumatoid arthritis and leaky gut syndrome.
How interesting that many of the fruits and vegetables she lists as having high fiber are also low carb! She forgot a few, though:

Spinach, frozen; 1 cup: 9 grams fiber
Asparagus, boiled; 1 cup: 3.8 grams fiber
Flax seed; 3 tablespoons: 6 grams fiber
Green beans, steamed; 1 cup: 4 grams fiber

Hmmm...just with those 4, I'd be nearly at 25 grams of fiber for the day and still well below 20 grams of [net] carb.