New discoveries about our gut microbiome (the community of viruses, bacteria, fungi) keep occurring. There is growing evidence that certain bacterial species in the gut are associated with cholesterol levels and heart disease.
Adding to the evidence, a recent study found that people with higher levels of several species of Oscillibacter bacteria had lower cholesterol levels than people without or diminished levels of these bacteria. The researchers than found (in the lab) that these species of Oscillibacter bacteria actually take up and metabolize artery-clogging cholesterol, which could explain the lower cholesterol levels.
By the way, other species (e.g., Eubacterium coprostanoligenes) were also associated with lower cholesterol levels in the study. The same people with higher levels of beneficial bacteria also had greater diversity of gut bacteria, which is considered a sign of gut health.
Species of Oscillibacter bacteria are not available in any supplements at this time. You'll just have to eat a diet that feeds and nurtures beneficial gut microbes.
And what is a health-promoting diet? A recent study found that a diet rich in fruits, vegetables, whole grains, nuts, seeds, legumes, and olive oil promotes healthy bacteria in the gut, which are associated with good health. This also is a diet high in fiber. Think along the lines of a Mediterranean diet.
From Science Daily: Scientists link certain gut bacteria to lower heart disease risk
Changes in the gut microbiome have been implicated in a range of diseases including type 2 diabetes, obesity, and inflammatory bowel disease. Now, a team of researchers at the Broad Institute of MIT and Harvard along with Massachusetts General Hospital has found that microbes in the gut may affect cardiovascular disease as well. In a study published in Cell, the team has identified specific species of bacteria that consume cholesterol in the gut and may help lower cholesterol and heart disease risk in people.
Members of Ramnik Xavier's lab, Broad's Metabolomics Platform, and collaborators analyzed metabolites and microbial genomes from more than 1,400 participants in the Framingham Heart Study, a decades-long project focused on risk factors for cardiovascular disease. The team discovered that bacteria called Oscillibacter take up and metabolize cholesterol from their surroundings, and that people carrying higher levels of the microbe in their gut had lower levels of cholesterol. They also identified the mechanism the bacteria likely use to break down cholesterol.
The results suggest that interventions that manipulate the microbiome in specific ways could one day help decrease cholesterol in people. The findings also lay the groundwork for more targeted investigations of how changes to the microbiome affect health and disease.
Cholesterol cues
In the new study, the Broad team gained a more complete and detailed picture of the impact of gut microbes on metabolism. They combined shotgun metagenomic sequencing, which profiles all of the microbial DNA in a sample, with metabolomics, which measures the levels of hundreds of known and thousands of unknown metabolites. They used these tools to study stool samples from the Framingham Heart Study.
The approach uncovered more than 16,000 associations between microbes and metabolic traits, including one that was particularly strong: People with several species of bacteria from the Oscillibacter genus had lower cholesterol levels than those who lacked the bacteria. The researchers found that species in the Oscillibacter genus were surprisingly abundant in the gut, representing on average 1 in every 100 bacteria.
The researchers then wanted to figure out the biochemical pathway the microbes use to break down cholesterol. To do this, they first needed to grow the organism in the lab. Fortunately, the lab has spent years collecting bacteria from stool samples to create a unique library that also included Oscillibacter.
After successfully growing the bacteria, the team used mass spectrometry to identify the most likely byproducts of cholesterol metabolism in the bacteria. This allowed them to determine the pathways the bacteria uses to lower cholesterol levels. They found that the bacteria converted cholesterol into intermediate products that can then be broken down by other bacteria and excreted from the body. Next, the team used machine-learning models to identify the candidate enzymes responsible for this biochemical conversion, and then detected those enzymes and cholesterol breakdown products specifically in certain Oscillibacter in the lab.
The team found another gut bacterial species, Eubacterium coprostanoligenes, that also contributes to decreased cholesterol levels., that also contributes to decreased cholesterol levels. This species carries a gene that the scientists had previously shown is involved in cholesterol metabolism. In the new work, the team discovered that Eubacterium might have a synergistic effect with Oscillibacter on cholesterol levels, which suggests that new experiments that study combinations of bacterial species could help shed light on how different microbial communities interact to affect human health.
Microbial messages
The vast majority of genes in the human gut microbiome remains uncharacterized, but the team is confident that their success in pinpointing cholesterol-metabolizing enzymes paves the way for the discovery of other similar metabolic pathways impacted by gut microbes, which could be targeted therapeutically.
"There are many clinical studies trying to do fecal microbiome transfer studies without much understanding of how the microbes interact with each other and the gut," Li said. "Hopefully stepping back by focusing on one particular bug or gene first, we'll get a systematic understanding of gut ecology and come up with better therapeutic strategies like targeting one or a few bugs."