The Gut Metagenome Changes in Parallel to Waist Circumference, Brain Iron Deposition, and Cognitive Function

Context: Microbiota perturbations seem to exert modulatory effects on emotional behavior, stress-, and pain-modulation systems in adult animals; however, limited information is available in humans. Objective: To study potential relationships among the gut metagenome, brain microstructure, and cognitive performance inmiddle-aged, apparently healthy, obese and nonobese subjects after weight changes. Design: This is a longitudinal study over a 2-year period. Setting: A tertiary public hospital. Patients or Other Participants: Thirty-five (18 obese) apparently healthy subjects. Intervention(s): Diet counseling was provided to all subjects. Obese subjects were followed every 6 months. Main Outcome Measure(s): Brain relaxometry (using magnetic resonance R2*), cognitive performance (by means of cognitive tests), and gut microbiome composition (shotgun). Results: R2* increased in both obese and nonobese subjects, independent of weight variations. Changes in waist circumference, but not in body mass index, were associated with brain iron deposition (R2*) in the striatum, amygdala, and hippocampus in parallel to visual-spatial constructional ability and circulating beta amyloid A beta 42 levels. These changes were linked to shifts in gut microbiome in which the relative abundance of bacteria belonging to Caldiserica and Thermodesulfobacteria phyla were reciprocally associated with raised R2* in different brain nuclei. Of note, the increase in bacteria belonging to Tenericutes phylum was parallel to decreased R2* gain in the striatum, serum Ab42 levels, and spared visual-spatial constructional ability. Interestingly, metagenome functions associated with circulating and brain iron stores are involved in bacterial generation of siderophores. Conclusions: Changes in the gut metagenome are associated longitudinally with cognitive function and brain iron deposition.