Gut bacteria might hold the key to weight loss. A new study, conducted on animal models, found that gut bacteria led to drastic changes in weight.

Researchers in the new study gave a group of mice gut bacteria from either obese or thin people. They found that mice with obese peoples' gut bacteria were more likely to gain weight than the other mice.

For the study, University of Colorado took fecal bacteria from four sets of adult, female twins. One person in each pair was obese. The team then transplanted fecal bacteria to "germ-free" mice and fed them various diets, including a typical American diet.

"[The results] show that mice that get microbes from obese individuals gain more weight than those that get microbes from lean individuals," Rob Knight, an associate professor at the University of Colorado at Boulder and co-author of the study, told HealthDay. "In other words, the weight gain can be transmitted from humans to mice by transferring their microbes."

The research could help understand the effects of gut bacteria in weight gain in people. Designing therapeutics with human gut bacteria will take time due to cost and the obvious "ick" factor as it is gross to get other's gut bacteria in one's system.

But experts are hopeful that we might have an option. In the future, there could be "a way to swap bacteria that's not gross," Justin Sonnenburg, an assistant professor at the Stanford University School of Medicine told Healthday. "There may even someday be a pill you could take."

Mice tend to eat each others' feces. So, when researchers kept the obese mice and thin mice together, they transferred gut bacteria from one another. Researchers found that obese mice reduced weight gain when they fed on bacteria from thin twins.

Knight told Healthday that it is possible to reduce weight by gut-bacteria-transfer. However, research conducted on mice doesn't always translate to humans.

A previous study conducted by researchers at China had found out that a gut bacterium called dysbacteriosis  may be responsible for obesity in some people. A related study recently found that a good way to help the "good bacteria" grow in the gut is to include fiber in the diet.

The study is published in the journal Science.