Imbalanced Gut Bacteria Doesn’t Promote Obesity, Study Finds

25 Aug 2016 --- No clear common characteristic of microbiome in the digestive systems of obese people that makes them different from the microbiome of those with a healthy weight, a new study has found. 

The new study contradicts previous research, which suggested that ‘out of whack’ microscopic creatures inside our bodies could be linked to obesity.

However, the study from the University of Michigan Medical School, found no clear common characteristic of microbiome in the digestive systems of obese people that makes them different from the microbiome of those with a healthy weight.

This lack of a clear 'signature' was found across more than 1,000 volunteers, and indicates that there's much more complexity, and therefore much more to learn, when it comes to the relationship between our microbiome and our health.

Marc Sze, Ph.D., the U-M postdoctoral research fellow who published the analysis with his mentor, 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 non-obese 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."

Using machine-learning computing tools developed in Schloss's lab over recent years, they took into account all the data about the different microbe species present in an individual's microbiome, along with other information. They then tried to use it to predict whether that individual was obese or not.

While the tool worked somewhat when they used it on data from one of the 10 studies done by others, it no longer predicted obesity well at all when they used it on data from the other studies.

"There really is no one 'healthy' microbiome," says Schloss. "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."

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."

The team hopes to expand on this research, and explore other areas of gut health.

"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."

Schloss explained that the results from this study should encourage scientists to cross validate their studies more critically, saying, “the important thing in all microbiome work is to not take exciting initial results as the final word.”

“We, as microbiome scientists, need to move the science forward and think more critically about the results we get. There's a need to cross-validate, and to understand that we might get different results with different populations."