IMO my only concern is their dats shows they were actually able to maintain a pretty controlled diet for each participant, I wonder how selection was done. I also would've appreciated some bomb calorimetry of fecal samples, similar to [0] which is the widely cited paper that does link general fiber intake to a lower level of caloric/energy absorption.

Baer, David J., et al. "Dietary fiber decreases the metabolizable energy content and nutrient digestibility of mixed diets fed to humans." The Journal of nutrition 127.4 (1997): 579-586.