Researchers at the University of Colorado Boulder did not plan to study weight loss.

Initially, they only wanted to see if injecting mice with a healthy form of bacteria could prevent inflammation in the brain and anxiety behavior that can result from a high-sugar, high-fat diet. While the bacteria did reduce biomarkers of neuro-inflammation and it did reduce anxiety behavior, it also prevented the mice from gaining weight and adipose tissue, or body fat, despite their poor diet.

“This has the potential to really challenge our ideas about what’s driving the current epidemic in obesity worldwide in urban societies,” CU Boulder professor Christopher Lowry said. “Of course, poor diet and lack of exercise (contribute), but is there another factor that we haven’t recognized?”

Lowry said that factor could be the importance of being exposed to healthy bacteria, known as “old friends.” People lost contact with these bacteria, which can regulate the immune system and suppress inflammation, as humanity transitioned to a modern- urban society.

Mycobacterium vaccae, or M. vaccae, was the bacteria used in the study and is commonly found in soil. Lowry said it has some pretty amazing properties.

“It can prevent allergic airway inflammation, can prevent stress inducted inflammation and promote stress resilience in a number of different animal model systems,” he said.

In the study, half mice were fed a healthy diet and the other half an unhealthy diet. Half of each group were treated with M. vaccae and the other half were not. The mice fed unhealthy diets without M. vaccae gained weight and fat, as expected. But, there was no difference in weight gain between the mice with an unhealthy diet who received M. vaccae and the mice with the healthy diets.

“The main finding from our study that was very unexpected was getting these subcutaneous injections of M. vaccae prevented the excess of weight gain, excess of visceral adipose tissue that is induced from chronic consumption of a western diet,” CU Boulder doctoral candidate Luke Desmond said. “This was very shocking because our main goal of this study was to look at the effects of M. vaccae with new inflammation, anxiety-like behavior and reproductive health. This was not our main goal.”

Lowry said M. vaccae had health benefits they didn’t anticipate.

“Obesity can increase inflammation and then this increased inflammation can exacerbate obesity,” Lowry said. “What was surprising is we could interrupt that cycle and actually prevent any weight gain in this study.”

In partnership with CU Boulder’s Venture Partners, the university’s commercialization arm that supports startup companies, Lowry and his colleagues are in the early stages of launching a startup called Kioga to pursue new microbe-based ingredients for preventing weight gain and promoting health.

Desmond has a second experiment planned to see whether M. vaccae can reduce excess body fat. He plans to inject the bacteria into obese mice to see if it will reduce their weight to a healthy, normal state.

“The next goal would be to see if M. vaccae can actually treat obesity,” he said.

The researchers also wonder if the bacteria can have the same effect given orally. Desmond said it’s likely people will find an oral administration more appealing than an injection, which would become important as it moves toward clinical trials. One application, aside from an injection, could be adding M. vaccae to nutritional supplements or food products someday.

Desmond said it appears promising that M. vaccae will work and have similar effects in humans. Lowry cited how M. vaccae has been studied in human clinical trials for cancer, and while it didn’t prolong life, it increased overall emotional health and cognitive function and decreased nausea and pain.

“Their overall quality of life increased and so this is giving us hope that we would see similar effects of M. vaccae in humans as we see in these animal models,” Lowry said.