As well as promoting the inflammation that leads to metabolic syndrome, altered gut microbiota promotes chronic inflammatory diseases such as Crohn's disease.
- A large waistline
- High levels of triglyceride (a type of fat found in the blood)
- Low high-density lipoprotein (HDL) cholesterol level
- High fasting blood sugar.
People with metabolic syndrome are twice as likely to develop heart disease and five times as likely to develop diabetes as the general population, according to the National Institutes of Health.
The American Heart Association report that about 34% of American adults have metabolic syndrome, and it is becoming more common, prompting scientists to investigate possible causes.
The team behind the new study - from Georgia State University (Atlanta) and Cornell University (Ithaca, NY) - had found in previous research that altered gut microbiota (intestinal bacteria) plays a role in metabolic syndrome.
New study explains mechanisms identified in previous research
According to Dr. Andrew Gewirtz, a professor in the Institute for Biomedical Sciences at Georgia State, the new study has filled in the details about how these mechanisms work.
"It's the loss of TLR5 on the epithelium," he explains, "the cells that line the surface of the intestine and their ability to quickly respond to bacteria. That ability goes away and results in a more aggressive bacterial population that gets closer in and produces substances that drive inflammation."
In a model of mouse siblings, the researchers demonstrated that the altered gut microbiota that promotes inflammation is more aggressive than other bacteria in infiltrating the epithelium.
Some of the mice in the study were missing the TLR5 gene, which the researchers found caused alterations in the inflammation-driving bacteria that promoted metabolic syndrome.
Dr. Ruth Ley, of the departments of Microbiology and Molecular Biology at Cornell, explains the findings:
"These results suggest that developing a means to promote a more healthy microbiota can treat or prevent metabolic disease.
They confirm the concept that altered microbiota can promote low-grade inflammation and metabolic syndrome and advance the underlying mechanism. We showed that the altered bacterial population is more aggressive in infiltrating the host and producing substances, namely flagellin and lipopolysaccharide, that further promote inflammation."
In that study, participants followed either a low-fat diet, a Mediterranean diet supplemented with nuts or a Mediterranean diet supplemented with extra-virgin olive oil, and they were followed for an average of 4.8 years.
The participants who followed the Mediterranean diets experienced a reduction in blood glucose levels and abdominal obesity. At the start of the study, 64% of participants had metabolic syndrome. However, by the end of the study, 28.2% of the participants following Mediterranean diets no longer met the diagnostic criteria for metabolic syndrome.
Other associated health benefits of the Mediterranean diet are investigated in our Knowledge Center article.