SOURCES: Jingyuan Fu, Ph.D., associate professor, genetics, University Medical Center Groningen, the Netherlands; Lea Chen, M.D., gastroenterologist, NYU Langone Medical Center, New York City; Sept. 10, 2015, Circulation Research, online
THURSDAY, Sept. 10, 2015 (HealthDay News) -- The size of your waistline may depend to some degree on the specific bacteria dwelling within your gut, new research suggests.
The study, of nearly 900 Dutch adults, found that certain gut bacteria might help determine not only body fat levels, but also blood concentrations of HDL cholesterol and triglycerides.
HDL is the "good" cholesterol that helps maintain a healthy heart; triglycerides are another type of blood fat that, in excess, can contribute to heart disease.
This is the first study to offer "solid evidence" that gut bacteria are linked to cholesterol and triglyceride levels, said lead researcher Jingyuan Fu.
But it does not prove that the bacteria directly alter people's blood fats, stressed Fu, an associate professor of genetics at University Medical Center Groningen, in the Netherlands.
So it's too early to recommend probiotic supplements for heart disease prevention, experts said. However, the findings add to growing evidence that the intestinal microbiome plays an important role in human health.
The term "microbiome" refers to the trillions of bacteria and other microbes that naturally dwell in the gut.
As recent research has revealed, those bugs do much more than support good digestion: They aid in everything from immune function, to metabolizing drugs to producing vitamins, anti-inflammatory compounds and even chemicals that relay messages among brain cells.
Studies have also suggested that when the microbiome lacks diversity, that may contribute to health conditions such as obesity, asthma and type 1 diabetes.
This latest study "contributes important information to our understanding of the gut microbiome and health risks, in particular cardiovascular disease," said Dr. Lea Chen, a gastroenterologist and microbiome researcher at NYU Langone Medical Center, in New York City.
The findings, published online Sept. 10 in the journal Circulation Research, are based on 893 adults ranging in age from 18 to 80. Fu's team analyzed fecal samples to get a snapshot of each person's intestinal microbiome.
Overall, the researchers found 34 types of bacteria that were associated with people's triglycerides and HDL levels, and with body mass index (BMI) -- a measure of weight in relation to height.
The investigators estimated that the gut microbiome explained 4 percent to 6 percent of the variance in BMI, triglycerides and HDL across the study group.
That's a "modest" impact, Chen pointed out. Plus, it's not clear that the microbiome is the cause at all.
"The identified gut bacteria could be driving changes in BMI or cholesterol, or they could merely be the byproduct of these factors," said Chen, who was not involved in the study.
A few of the bacteria highlighted in the study are known to be involved in metabolizing bile acids that affect cholesterol levels. But Chen and Fu both said much more research is needed to understand how different gut bacteria function in relation to cholesterol and other risk factors for heart disease.
"At the current stage, this field is still in its infancy," Fu said.
Researchers do not yet know how to define a "healthy" microbiome. But studies have suggested that modern living may be decreasing the diversity of the typical American's gut microbiome -- and that lack of diversity may be related to higher disease risks.
What makes a microbiome less diverse? Experts suspect that C-sections and lack of breast-feeding are two factors: C-sections deprive newborns of beneficial bacteria from the birth canal, while breast milk feeds gut bacteria.
Diets filled with processed foods are also thought to be at fault.
What's key, Fu said, is that the gut microbiome can be changed through diet -- unlike age, genes and certain other heart disease risk factors. But it's not clear exactly what changes might support a healthy heart.
For now, Chen suggested that people stick with proven ways -- which include eating a diet rich in fruits, vegetables, fish, fiber-rich grains and other "whole" foods.
The American Society for Microbiology has an overview of the human microbiome.