How gut bacteria may be sabotaging your weight loss efforts

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Can the make-up of your gut microbiome affect the success of a weight loss intervention? A unique new study is indicating this is certainly possible, identifying several mechanisms by which gut bacteria can either help or hinder weight loss.

A small 2018 study from researchers at the Mayo Clinic investigated the gut microbiome differences between those responding effectively to a weight loss program and those who did not lose much weight at all. As well as identifying several specific types of gut bacteria that seemed to correlate with successful weight loss, the research indicated subjects with an increased capacity for carbohydrate metabolism tended to be less successful at losing weight.

A new study, this time from a team at the Institute for Systems Biology in Seattle, Washington, is zooming in even further on the microbial metabolic processes that distinguish effective weight loss from those who struggle to drop the pounds. The research began by collecting participant data from a large commercial wellness program using personalized behavioral interventions to improve overall health.

Data from around 5,000 participants with specific weight loss goals was initially analyzed, and ultimately the researchers whittled that down to a cohort of around 100 individuals. Half of those successfully lost over one percent of their total body weight per month across a six-to-12-month period. The other half maintained a stable body-mass index over the same period of time.

Genetic material from both blood and stool was analyzed to investigate the differences between the two groups. Ultimately the researchers found 31 key functional genomic features they claim differentiated the individual weight loss responses.

“We suggest that dietary energy harvest, host-microbe substrate competition, and modulation of host inflammation by commensal bacteria may be, in part, responsible for determining host responses to weight loss interventions, independent of baseline BMI or metabolic health state,” the researchers write in the newly published study. “Gut ecosystems optimized for fermentative metabolism and higher bacterial growth rates appear to be conducive to weight loss.”

Following on from the Mayo Clinic’s 2018 findings, this new research again found those who struggled with weight loss display increased capacity for breaking down starches into absorbable sugars. Lead author on the new study, Christian Diener, says his findings suggest the gut microbiome is a “major player” in governing the success or failure of a given weight loss intervention.

“Our results underscore the fact that our gut microbiome is an important filter between the food we consume and our bloodstream,” says Diener. “Weight loss may be especially hard when our gut bacteria slow their own growth, while also breaking down dietary fibers into energy-rich sugars that make their way into our bloodstream before they can be fermented into organic acids by the microbiota.”

More work is certainly needed to validate these findings with detailed longitudinal data because, while the study does identify certain types of gut bacteria that could be hindering weight loss, the science is certainly not near the point where singular anti-obesity probiotics can be offered.

If anything, the research builds on the growing hypothesis that the classic “calorie in/calorie out” paradigm may be fundamentally flawed. These findings offer compelling evidence to suggest obesity could be greatly influenced by metabolic dysregulation mediated by gut bacteria, as opposed to a simple imbalance between calories consumed and energy expended.

But there are more immediate outcomes that could come from this research. Sean Gibbons, corresponding author on the new study, says it is possible to use these findings to generate personalized weight loss interventions that are customized to an individual’s microbiome.

“At a minimum, this work may lead to diagnostics for identifying individuals who will respond well to moderate healthy lifestyle changes, and those who may require more drastic measures to achieve weight loss,” says Gibbons.

The new study was published in the journal mSystems.