Gut microbiome and blood lipids: Blood cholesterol reduction linked with growth in Clostridia leptum

The study is a follow-up to a clinical trial which looks at how the consumption of three different cooking oils – one containing refined olive oil and the other two containing refined rice bran oil, refined flaxseed oil, and refined sesame oil – could affect blood cholesterol.

The refined olive oil was high in mono-unsaturated fatty acids (MUFA) while the other two oil blends were high in omega-3 PUFA and ALA.

In all three groups, Clostridium leptum ​was reported to have greatly increased in number.

However, gut microbiome analysis showed that the cooking oil with the highest concentration of omega-3 PUFA was associated with faster and more robust responses in the intestinal microbiota.

The analysis was performed by researchers from the National University of Singapore’s Centre for Translational Medicine, Nanyang Technological University’s Division of Chemistry and Biological Chemistry, Clinical Nutrition Research Centre at A*STAR, Genome Institute of Singapore, and Wilmar (Shanghai) Biotechnology R&D Centre.

Findings of the analysis were published in Biofilms and Microbiomes. ​

“Multi-factor analysis of relationships between the gut microbiota composition at various taxonomic ranks and the clinical trial parameters revealed the association between beneficial effects of the dietary intervention on the blood lipid profile with abundance of Clostridia class of the gut microbiota. ​ ​

“This microbiota feature was upregulated in the course of the dietary intervention and associated with various plasma markers of metabolic health status, such as triglycerides, Apolipoprotein B and total cholesterol to HDL ratio in a beneficial way,” ​the researchers said.

This analysis was performed as part of an eight-week clinical trial looking at how the three aforementioned cooking oils could affect the blood cholesterol levels of over 120 Chinese adults with borderline hypercholesterolemia, or simply, high blood cholesterol.

The oil blends used were provided were provided by Wilmar International.

Results of the trial, published in The Journal of Nutrition​, ​showed that there were significant reductions in serum total cholesterol, the “bad” LDL cholesterol, triglycerides, and serum glucose for all three invention groups.

However, there was no effects of the intervention on the “good” HDL-cholesterol.

Butyrate production activated? ​

Following the trial, the researchers conducted a microbiome analysis to see if the observations were associated with any changes in the gut microbiome.

During which, they found that the cooking oil with the highest concentration of omega-3 PUFA was associated with faster and more robust gut microbiota changes, including the elevation of alpha-diversity.

The researchers have come up with three potential reasons.

The first is that a higher concentration of omega-3 PUFA and ALA could have promoted faster microbiota responses to the dietary intervention.

Another reason could be due to the phytonutrients content in high omega-3 PUFA oils.

They cited the findings of an animal study​, which showed that oryzanol from rice bran oil was shown to shift the microbial compositional pattern by lowering the Firmicutes/Bacteroidetes ratio.

Third, they suggested that the high omega-3 PUFA oils could have changed the blood lipid profile by activating the production of butyrate, a short-chain fatty acid.

“Butyrate production is being discussed as a plausible process mediating the observed beneficial influence on the plasma lipid profile,”​ they said.

The key bacteria genus ​

The bacteria genus, Clostridium, ​could have been involved in the improvement of blood lipids, said the researchers.

In the course of the dietary intervention, 11 bacterial species had changed their relative abundance, including three Clostridium​ species.

Five Clostridium​ species were among the top 37 species ranked by significance and of which, four showed a tendency to increase in abundance in the course of the clinical trial.

The greatest increase was seen in the species—Clostridium leptum​— which had increased during the dietary intervention in all the three study groups.

This means that this bacteria species was the most responsive to the cooking oils consumed in the study.

“The top responsive species, Clostridium leptum, showed the statistical significance level 4 orders of magnitude better compared to the next responder species in the ranked list, as well as the highest coefficient of the association.​

“The pronounced increase in intestinal Clostridium leptum species observed consistently in all the 3 groups of this study, may be related to the increase in the unsaturated fatty acids,” ​the researchers said.

Clostridium leptum ​is a known butyrate producer that can thrive in the gut microbial community in response to dietary oil supplementation, at least in this particular study.

Reproducibility of this effect in other geographic locations and local microbiome composition contexts would require further studies, the researchers said.

Source: biofilms and microbiomes​

Gut microbiome responses to dietary intervention with hypocholesterolemic vegetable oils​

https://doi.org/10.1038/s41522-022-00287-y​

Authors: Lim, R.R.X., Park, M.A., Wong, L.H. et al​