A Walnut-Enriched Diet Affects Gut Microbiome in Healthy Caucasian Subjects: A Randomized, Controlled Trial.

Nutrients. 2018 Feb 22;10(2). pii: E244. doi: 10.3390/nu10020244. Bamberger C1, Rossmeier A2, Lechner K3, Wu L4, Waldmann E5, Fischer S6, Stark RG7, Altenhofer J8, Henze K9, Parhofer KG10. Author information 1 Department of Internal Medicine 4, Ludwig-Maximilians University Munich, Marchioninistraße 15, 81377 Munich, Germany. charlotte.bamberger@med.uni-muenchen.de. 2 Department of Internal Medicine 4, Ludwig-Maximilians University Munich, Marchioninistraße 15, 81377 Munich, Germany. andreas.rossmeier@med.uni-muenchen.de. 3 Department of Internal Medicine 4, Ludwig-Maximilians University Munich, Marchioninistraße 15, 81377 Munich, Germany. katharina.lechner@mri.tum.de. 4 Department of Internal Medicine 4, Ludwig-Maximilians University Munich, Marchioninistraße 15, 81377 Munich, Germany. wuliya@pennmedicine.upenn.edu. 5 Department of Internal Medicine 4, Ludwig-Maximilians University Munich, Marchioninistraße 15, 81377 Munich, Germany. elisa.waldmann@med.uni-muenchen.de. 6 ZIEL-Institute for Food & Health Core Facility, Technical University Munich, Weihenstephaner Berg 3, 85354 Freising, Germany. sandra.fischer@tum.de. 7 Helmholtz-Zentrum Munich, Institute for Health Economics and Healthcare Management, 85764 Neuherberg, Germany. r.stark@helmholtz-muenchen.de. 8 Department of Internal Medicine 4, Ludwig-Maximilians University Munich, Marchioninistraße 15, 81377 Munich, Germany. julia.altenhofer@med.uni-muenchen.de. 9 Department of Internal Medicine 4, Ludwig-Maximilians University Munich, Marchioninistraße 15, 81377 Munich, Germany. kerstin.henze@med.uni-muenchen.de. 10 Department of Internal Medicine 4, Ludwig-Maximilians University Munich, Marchioninistraße 15, 81377 Munich, Germany. klaus.parhofer@med.uni-muenchen.de. Abstract Regular walnut consumption is associated with better health. We have previously shown that eight weeks of walnut consumption (43 g/day) significantly improves lipids in healthy subjects. In the same study, gut microbiome was evaluated. We included 194 healthy subjects (134 females, 63 ± 7 years, BMI 25.1 ± 4.0 kg/m²) in a randomized, controlled, prospective, cross-over study. Following a nut-free run-in period, subjects were randomized to two diet phases (eight weeks each); 96 subjects first followed a walnut-enriched diet (43 g/day) and then switched to a nut-free diet, while 98 subjects followed the diets in reverse order. While consuming the walnut-enriched diet, subjects were advised to either reduce fat or carbohydrates or both to account for the additional calories. Fecal samples were collected from 135 subjects at the end of the walnut-diet and the control-diet period for microbiome analyses. The 16S rRNA gene sequencing data was clustered with a 97% similarity into Operational Taxonomic Units (OTUs). UniFrac distances were used to determine diversity between groups. Differential abundance was evaluated using the Kruskal-Wallis rank sum test. All analyses were performed using Rhea. Generalized UniFrac distance shows that walnut consumption significantly affects microbiome composition and diversity. Multidimensional scaling (metric and non-metric) indicates dissimilarities of approximately 5% between walnut and control (p = 0.02). The abundance of Ruminococcaceae and Bifidobacteria increased significantly (p < 0.02) while Clostridium sp. cluster XIVa species (Blautia; Anaerostipes) decreased significantly (p < 0.05) during walnut consumption. The effect of walnut consumption on the microbiome only marginally depended on whether subjects replaced fat, carbohydrates or both while on walnuts. Daily intake of 43 g walnuts over eight weeks significantly affects the gut microbiome by enhancing probiotic- and butyric acid-producing species in healthy individuals. Further evaluation is required to establish whether these changes are preserved during longer walnut consumption and how these are linked to the observed changes in lipid metabolism. KEYWORDS: butyric acid; cholesterol; diet; gut microbiome; lipids; nuts; prebiotic; probiotic; walnuts PMID: 29470389 PMCID: PMC5852820 DOI: 10.3390/nu10020244 [Indexed for MEDLINE] Free PMC Article Share on FacebookShare on TwitterShare on Google+