Gut Bacteria Leads to Obesity?

 

In recent years, researchers studying the microscopic creatures inside our bodies reported possible links between obesity and out-of-balance microbes.
SEE ALSO: Discovery of Gut Bacteria in Critically Ill Lungs Could Change ICU Care
But new research, which pooled data from many of those past studies, disputes the idea that extra pounds may stem from an imbalance in the microbiome.
The study, published in the journal mBio, finds no clear common characteristic of the microbiomes in the digestive systems of people who are obese compared to those of a healthy weight.
This lack of a clear signature across more than 1,000 volunteers from 10 of the largest studies to date may disappoint those looking for an explanation for obesity, as well as the companies that sell products claiming to alter the gut’s microscopic population through fiber, nutrients and “good” bacteria.
But to the researchers from the University of Michigan Medical School, it’s exciting. It means that there’s much more complexity to discover on the relationship between our microbiome and our health.
Marc Sze, Ph.D., the U-M postdoctoral research fellow who published the analysis with U-M microbiology professor Patrick Schloss, Ph.D., says the scale of the obesity problem means it’s that much more important to be certain about the science.
“Obesity is currently a health risk of epidemic proportions, and many have suggested that the bacterial microbiome is not only different between obese and nonobese, but also can predict obesity,” says Sze. “We wanted to see if this was really what the existing literature suggested, since these claims could have a lot of positive impact on the management of this epidemic if true.”
Adds Schloss, “In the end, we found that there are no clear signatures or predictors of obesity across the microbiome data reported thus far, and that if there is any signature at all related to diversity of microbes, it’s not biologically useful. This is a cautionary tale that points to the need to do more work to clarify what we know and don’t know.”

"This is a cautionary tale that points to the need to do more work to clarify what we know and don’t know."

Pat Schloss, Ph.D.

Pooling the data

The idea that obesity and imbalanced microbiomes are linked started with the observation that obese animals tended to have a certain ratio of two groups of bacteria species. That led to the studies in humans — some with just a few dozen participants — which grabbed headlines in recent years.
But people and rodents are very different, and large samples of people are needed to say anything definitive about human health and its link to the microbiome.
Sze and Schloss used machine-learning computing tools developed in Schloss’s lab to perform their analysis, including a program called mothur that gives researchers a free open-source tool for studying the vast amount of data emerging from microbiome studies.
They created a classification model that takes into account all the data about the different microbe species present in an individual’s microbiome and other information. They then tried to use it to predict whether that individual was obese.
While the tool worked somewhat on data from one of the 10 past studies, it did not predict obesity well at all when used on data from the other papers.
“There really is no one ‘healthy’ microbiome,” says Schloss, a member of the Host Microbiome Initiative at U-M Medical School. “You could look at hundreds of people, and they could all have very different populations of microbes in their guts. So the idea that we can correct your microbiome by doing one simple thing also doesn’t hold up.”
That said, generally accepted healthy eating habits that give gut microbes lots of fiber and nutrients to chew on can’t hurt, he adds.

Next steps for the research

The researchers created an open online site where other researchers can see the U-M team’s work and add more data from gut microbiome studies in obese and nonobese people to continue the search for links.
SEE ALSO: Study: Water Intake Overlooked in Obese Individuals
As the data grow, the trustworthiness of the findings will, too. And perhaps specific linkages and signatures will be found in future.
The team is also developing a similar tool for evaluating the gut microbiome’s possible links to colon cancer. Earlier this year, they published results from an analysis of several hundred people, and showed that their tool has reasonable accuracy in detecting the microbiome signatures more common in people with colon cancer than those without.
“We will continue to apply these approaches to look at the microbiome and colorectal cancer,” says Sze. “We also want to take the lessons that we earned from working with large data sets and apply them to our research on how the bacterial microbiome in families might have an impact on inherited colorectal cancers.”
Ultimately, the goal of this work could be a new diagnostic tool to detect colon cancer or cancer risk from a stool sample.
Another potential area for study is not the diversity of microbes present in the gut, but rather the extent they are producing the breakdown products of their role in the digestive process. These molecules, called metabolites, may form a more meaningful signature of microbe activity.
No matter what, Schloss says, the important thing in all microbiome work is to not take exciting initial results as the final word.
“We need to move the science forward and think more critically about the results we get,” he says. “There’s a need to cross-validate, and to understand that we might get different results with different populations.”

Gut bacteria may influence weight during childhood and adolescence, say researchers, who found that the population of gut microbes among obese children and teenagers differs to that of normal-weight youth.

Researchers identified different gut microbiota in obese children and teenagers, compared with normal-weight peers.

Senior author Dr. Nicola Santoro, of the Department of Pediatrics at Yale University in New Haven, CT, and colleagues report their findings in the Journal of Endocrinology & Metabolism.
According to the Centers for Disease Control and Prevention (CDC), over the past 30 years, obesity rates have more than doubled in children and quadrupled in adolescents.
These rising rates have fueled a major public health concern; youths who are obese are more likely to be obese in adulthood, which may raise their risk for stroke, heart disease, type 2 diabetes, and some types of cancer.
As such, there is a need to identify strategies that may help prevent or treat childhood obesity, and Dr. Santoro and team believe they may be one step closer to such a strategy.
Their study included 84 children and adolescents aged 7-20 years, of whom seven were overweight, 15 were normal weight, 27 were obese, and 35 were severely obese.
The researchers analyzed the gut microbiota - the population of microbes living in the intestine - and blood samples of all participants; blood samples were assessed for levels of short-chain fatty acids, which are produced by some forms of gut bacteria.
Participants also underweight magnetic resonance imaging (MRI), which allowed the researchers to measure body fat distribution.

Four gut microbiota groups more abundant in obese children, teens

From their analysis, the researchers identified eight groups of gut microbiota that were associated with levels of body fat.
Four of the eight gut microbiota groups were much more abundant in children and teenagers who were obese, the team reports, and they were found to digest carbohydrates much more efficiently than those found in normal-weight counterparts.
When it came to the remaining four gut microbiota groups, the team found obese children and teenagers possessed these in significantly smaller amounts, compared with normal-weight peers.
What is more, children who were obese had higher levels of short-chain fatty acids in their blood than children who were a normal weight, and the team found a link between these fatty acids and fat production in the liver.
These results, the researchers say, suggest the liver can convert short-chain fatty acids into fat, and this fat accumulates in adipose tissue.
"This association could signal that children with certain gut bacteria face a long-term risk of developing obesity," says Dr. Santoro.
While these findings may not be welcome news, there is a brighter side; Dr. Santoro told Medical News Today that the results could lead to new ways to combat obesity in children and adolescents.

"These data try to explain the physiopathology behind the relationship between gut flora and obesity. In future, the identification of species underlying this association might lead to targeted treatments."

Dr. Nicola Santoro

MNT asked Dr. Santoro about any plans for further research into the link between gut microbiota and weight among youth.
"The next step would be to understand the fate of short-chain fatty acids derived from the gut flora and how they are integrated in and modulate the human metabolism," she told us.
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Written by Honor Whiteman