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

Study information

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Reviewed Marked as Reviewed by Atrayees on 2023-7-18

study design

randomized controlled trial

Citation

PMID PubMed identifier for scientific articles.

29470389

DOI Digital object identifier for electronic documents.

10.3390/nu10020244

URI

Authors

Bamberger C, Rossmeier A, Lechner K, Wu L, Waldmann E, Fischer S, Stark RG, Altenhofer J, Henze K, Parhofer KG

Journal

Nutrients

Year

2018

Keywords:

butyric acid, cholesterol, diet, gut microbiome, lipids, nuts, prebiotic, probiotic, walnuts

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.

Experiment 1

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Curated date: 2021/01/10

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Subjects

Location of subjects

Germany

Host species Species from which microbiome was sampled. Contact us to have more species added.

Homo sapiens

Body site Anatomical site where microbial samples were extracted from according to the Uber Anatomy Ontology

Feces Cow dung,Cow pat,Droppings,Dung,Excrement,Excreta,Faeces,Fecal material,Fecal matter,Fewmet,Frass,Guano,Matières fécales@fr,Merde@fr,Ordure,Partie de la merde@fr,Piece of shit,Porción de mierda@es,Portion of dung,Portion of excrement,Portion of faeces,Portion of fecal material,Portion of fecal matter,Portion of feces,Portion of guano,Portion of scat,Portionem cacas,Scat,Spoor,Spraint,Stool,Teil der fäkalien@de,Feces,feces

Condition The experimental condition / phenotype studied according to the Experimental Factor Ontology

Diet Dietary,Diets,Diet,diet

Group 0 name Corresponds to the control (unexposed) group for case-control studies

after walnut diet

Group 1 name Corresponds to the case (exposed) group for case-control studies

before walnut diet

Group 1 definition Diagnostic criteria applied to define the specific condition / phenotype represented in the case (exposed) group

before walnut consumption

Group 0 sample size Number of subjects in the control (unexposed) group

135

Group 1 sample size Number of subjects in the case (exposed) group

135

Antibiotics exclusion Number of days without antibiotics usage (if applicable) and other antibiotics-related criteria used to exclude participants (if any)

excluded those on "antibiotic therapy"

Lab analysis

Sequencing type

16S

16S variable region One or more hypervariable region(s) of the bacterial 16S gene

V3-V4

Sequencing platform Manufacturer and experimental platform used for quantifying microbial abundance

Illumina

Statistical Analysis

Data transformation Data transformation applied to microbial abundance measurements prior to differential abundance testing (if any).

relative abundances

Statistical test

Kruskall-Wallis

Significance threshold p-value or FDR threshold used for differential abundance testing (if any)

0.05

MHT correction Have statistical tests be corrected for multiple hypothesis testing (MHT)?

No

Alpha Diversity

Shannon Estimator of species richness and species evenness: more weight on species richness

unchanged

Simpson Estimator of species richness and species evenness: more weight on species evenness

unchanged

Richness Number of species

unchanged

Signature 1

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Curated date: 2021/01/10

Curator: Lora Kasselman

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Source: Figure 4b, 5a, and text

Description: Most abundant Operational Taxonomic Units for both walnut and control phase at genus level. Significant different OTUs are marked with by using * and p-values. pvalues were calculated using a pairwise Fisher test.

Abundance in Group 1: increased abundance in before walnut diet

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Anaerostipes
Oscillospiraceae

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Signature 2

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Curator: Lora Kasselman

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Source: Figure 4b, 5a, and text

Description: Most abundant Operational Taxonomic Units for both walnut and control phase at genus level. Significant different OTUs are marked with by using * and p-values. pvalues were calculated using a pairwise Fisher test.

Abundance in Group 1: decreased abundance in before walnut diet

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Oscillospiraceae
Bifidobacterium
Blautia

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Experiment 2

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Curated date: 2021/01/10

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Differences from previous experiment shown

Subjects

Group 0 name Corresponds to the control (unexposed) group for case-control studies

replace both

Group 1 name Corresponds to the case (exposed) group for case-control studies

carbohydrate replacement (with walnuts)

Lab analysis

Statistical Analysis

Confounders controlled for Confounding factors that have been accounted for by stratification or model adjustment

age, body mass index, smoking behavior, triglycerides, Confounders controlled for: "LDL cholesterol" is not in the list (abnormal glucose tolerance, acetaldehyde, acute graft vs. host disease, acute lymphoblastic leukemia, acute myeloid leukemia, adenoma, age, AIDS, alcohol consumption measurement, alcohol drinking, ...) of allowed values.LDL cholesterol

Signature 1

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Reviewed Marked as Reviewed by Atrayees on 2023-7-18

Curated date: 2021/01/10

Curator: Lora Kasselman

Revision editor(s): WikiWorks, Atrayees

Source: 5a and text

Description: Most abundant Operational Taxonomic Units for both walnut and control phase at genus level. Significant different OTUs are marked with by using * and p-values. pvalues were calculated using a pairwise Fisher test.

Abundance in Group 1: decreased abundance in carbohydrate replacement (with walnuts)

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Gemmiger
Fusicatenibacter
Bacteroides

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Experiment 3

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Reviewed Marked as Reviewed by Atrayees on 2023-7-18

Curated date: 2021/01/10

Curator: WikiWorks

Revision editor(s): WikiWorks, Atrayees

Differences from previous experiment shown

Subjects

Group 0 name Corresponds to the control (unexposed) group for case-control studies

fat replacement (with walnuts)

Group 1 name Corresponds to the case (exposed) group for case-control studies

replace both

Lab analysis

Statistical Analysis

Signature 1

EditHistoryDelete

Flag for review

Your review change was submitted

Reviewed Marked as Reviewed by Atrayees on 2023-7-18

Curated date: 2021/01/10

Curator: Lora Kasselman

Revision editor(s): WikiWorks, Atrayees

Source: 5a and text

Description: Most abundant Operational Taxonomic Units for both walnut and control phase at genus level. Significant different OTUs are marked with by using * and p-values. pvalues were calculated using a pairwise Fisher test.

Abundance in Group 1: increased abundance in replace both

NCBI	Quality Control	Links
Gemmiger
Fusicatenibacter
Bacteroides

Revision editor(s): WikiWorks, Atrayees