Thank you for your detailed response! Yes, I realize the improvement in the study was small on average, but the results were somewhat better for those who started the study overweight. The "jump start" that I saw in my own weight loss also served as psychological encouragement for me, as a post menopausal woman who has not seen results even from low-carb diets. We were not consciously trying to restrict calories, but as you say the additional fiber may have reduced our appetites. It's also possible that fiber reduces appetite through another mechanism, such as the one suggested in this 2014 article in Nature "Dietary fibre acts on brain to suppress appetite" https://www.nature.com/news/dietary-fibre-acts-on-brain-to-suppress-appetite-1.15127
Another possibility is that the additional fiber improved our gut health, as my son and I have both had to use antibiotics numerous times over the past ten years. The antibiotics may have reduced healthy diversity in our gut biome, which may make weight gain more likely. The NIH published a meta-analysis in March, 2020 of 16 studies of fiber, gut microbiota, and metabolic regulation. Although much more study is needed, the authors concluded that "The current review shows that dietary fiber has the potential to change the gut microbiota and alter metabolic regulation in humans."
In any case, I appreciate your thoughtful comments, and I agree that a low-carb diet works for many people. All the best, Claudia