The interplay between dietary fatty acids and gut microbiota influences host metabolism and hepatic steatosis

Dietary lipids can affect metabolic health through gut microbiota-mediated mechanisms, but the influence of lipid-microbiota interaction on liver steatosis is largely unknown. We investigate the impact of dietary lipids on human gut microbiota composition and the effects of microbiota-lipid interactions on steatosis in male mice. In humans, low intake of saturated fatty acids (SFA) is associated with increased microbial diversity independent of fiber intake. In mice, poorly absorbed dietary long-chain SFA, particularly stearic acid, induce a shift in bile acid profile and improved metabolism and steatosis. These benefits are dependent on the gut microbiota, as they are transmitted by microbial transfer. Diets enriched in polyunsaturated fatty acids are protective against steatosis but have minor influence on the microbiota. In summary, we find that diets enriched in poorly absorbed long-chain SFA modulate gut microbiota profiles independent of fiber intake, and this interaction is relevant to improve metabolism and decrease liver steatosis.

The raw metagenomic sequence data of the 114 human subjects from the Ironmet cohort have been deposited in the European Nucleotide Archive (ENA) under the project number PRJEB39631 with the accession numbers ERS4859818-ERS4859933 (https://www.ebi.ac.uk/ena/browser/view/PRJEB39631). The microarray data generated in this study have been deposited in NCBI GEO under accession code GSE222060 (https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi? acc=GSE222060). The mouse cecum 16S rRNA data generated in this study have been deposited in the European Nucleotide Archive (ENA) under accession code PRJEB58626 (https:// www.ebi.ac.uk/ena/browser/view/PRJEB58626). Data generated in this study are provided in the Source Data file.
Subjects from the human cohort (n = 117; 79 women, 35 men). Sex and gender were considered in the study design, all subjects were analyzed together. Sex was determined based on self-report. No sex-and gender-based analyses have been performed a priori and we have not performed adhoc analysis due to low number of replicates.
No data on race, ethnicity, or other socially relevant groupings was collected.
Population characteristics has been previously described in Arnoriaga-Rodriguez et al. (https://gut.bmj.com/ content/70/12/2283#T1). Consecutive middle-aged subjects, 27.2-66.6 years, were included. Patients with obesity (body mass index (BMI) !30 kg/m2) and age-matched and sex-matched subjects without obesity (BMI 18.5-<30 kg/m2), were eligible. Exclusion criteria were type 2 diabetes mellitus, chronic inflammatory systemic diseases, acute or chronic infections in the previous month; use of antibiotic, antifungal, antiviral or treatment with proton pump inhibitors; severe disorders of eating behaviour or major psychiatric antecedents; neurological diseases, history of trauma or injured brain, language

Recruitment
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Life sciences
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Life sciences study design
All studies must disclose on these points even when the disclosure is negative. The human study was performed on a cohort that was not a priori designed for the current study but where metagenome data, diet consumption and liver status were measured. This made it useful for the purpose of the study but did not allow selection of a sample size. Moreover, the primary outcome in the human study is microbiome composition which is composed of complex data which do not allow sample size calculation. Hence, no power calculation was performed. No power calculations were performed for the mouse studies. The number of replicates was based on experience from previous studies with similar design performed in our lab (https://www.sciencedirect.com/science/article/pii/S1550413115003897?via%3Dihub). The micobiota transfer experiment had 15 instead of 10 replicates since the experimental design may cause loss of mice and/or increased variance in outcome data.
No data were excluded from the human study.
In mouse experiments data points are missing due to loss samples, technical issues or other reasons. The reasons are stated along with the data in the Source data file.
The metabolic profile of mice fed MF and A were confirmed in a follow-up independent experiment (data not included in ms). All data obtained from this experiment replicated the results from the initial experiment.
Since the human study contained unique material and the mouse studies were very large no other experiments were replicated.
The design of the human study was cross-sectional and no prior division into groups was performed. Mice were divided into groups based on starting weight at the beginning of the experiment.
The investigators performing data collection in the human study did not have knowledge of the research question of the present study. For practial reasons analysis of data from the human study was not perform blinded. For practical reasons, it was impossible to perform mouse experiments and most downstream analyses blinded. The exceptions from this were lipid analysis and evaluation of histology that were performed blinded.