https://www.medscape.com/viewarticle/905962 Healthy adults had less bloating, increased well-being, and a small but significant weight loss on low-gluten (LG) compared with high-gluten (HG) diets, a study found. The differences appear linked to differences in dietary fiber associated with components of the two diets, not to gluten per se, the researchers report in an article published online November 13 in Nature Communications. "[T]he changes in colonic microbial composition and fermentation suggest that the effects of a low-gluten diet in healthy middle-aged adults may to some extent be driven by qualitative changes in dietary fibres upon reduction of gluten-rich food items rather than by the reduction of gluten intake itself," Oluf Pedersen, MD, Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen, Denmark, and colleagues write.
Maybe they were getting more fiber from fruits and vegetables rather than wheat products so they took in higher quality fibers with no added negatives associated with gluten and absorbtion of nutrients.