title: Energy-balance studies reveal associations between gut microbes, caloric load, and nutrient absorption in humans.
abstract: BACKGROUND
  Studies in mice indicate that the gut microbiome influences both sides of the energy-balance equation by contributing to nutrient absorption and regulating host genes that affect adiposity. However, it remains uncertain as to what extent gut microbiota are an important regulator of nutrient absorption in humans.
  
  
  OBJECTIVE
  With the use of a carefully monitored inpatient study cohort, we tested how gut bacterial community structure is affected by altering the nutrient load in lean and obese individuals and whether their microbiota are correlated with the efficiency of dietary energy harvest.
  
  
  METHODS
  We investigated dynamic changes of gut microbiota during diets that varied in caloric content (2400 compared with 3400 kcal/d) by pyrosequencing bacterial 16S ribosomal RNA (rRNA) genes present in the feces of 12 lean and 9 obese individuals and by measuring ingested and stool calories with the use of bomb calorimetry.
  
  
  RESULTS
  The alteration of the nutrient load induced rapid changes in the gut microbiota. These changes were directly correlated with stool energy loss in lean individuals such that a 20% increase in Firmicutes and a corresponding decrease in Bacteroidetes were associated with an increased energy harvest of ≈150 kcal. A high degree of overfeeding in lean individuals was accompanied by a greater fractional decrease in stool energy loss.
  
  
  CONCLUSIONS
  These results show that the nutrient load is a key variable that can influence the gut (fecal) bacterial community structure over short time scales. Furthermore, the observed associations between gut microbes and nutrient absorption indicate a possible role of the human gut microbiota in the regulation of the nutrient harvest. This trial was registered at clinicaltrials.gov as NCT00414063.
authors.affiliation: Obesity and Diabetes Clinical Research Section, National Institute of Diabetes, Digestive, and Kidney Diseases, National Institutes of Health, Phoenix, AZ 85016, USA. jumpertzr@mail.nih.gov
authors.forename: Reiner
authors.initials: R
authors.lastname: Jumpertz
authors.forename: Duc Son
authors.initials: DS
authors.lastname: Le
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Turnbaugh
authors.forename: Cathy
authors.initials: C
authors.lastname: Trinidad
authors.forename: Clifton
authors.initials: C
authors.lastname: Bogardus
authors.forename: Jeffrey I
authors.initials: JI
authors.lastname: Gordon
authors.forename: Jonathan
authors.initials: J
authors.lastname: Krakoff
mesh_terms: D000328:Adult; D001419:Bacteria / Q000302:isolation & purification*; D002149:Energy Intake; D004734:Energy Metabolism; D005502:Food; D041981:Gastrointestinal Tract / Q000378:metabolism / Q000382:microbiology*; D006801:Humans; D007408:Intestinal Absorption; D008297:Male; D008875:Middle Aged