What is in your gut may determine how much you weigh on the scale. The human gut contains a lot of organisms that help break down food. Recent research has suggested that manipulating the composition of the organisms in the gut can help people live a healthy life.

Now, a new research from University of Chicago has found that people can lose weight by manipulating the composition of organisms in the gut. According to researchers, in the future we may have vaccines and medications tailored to grow some types of beneficial bacteria in the gut that help people lose weight.

"Diet-induced obesity depends not just on calories ingested but also on the host's microbiome," said the study's senior author Yang-Xin Fu, MD, PhD, professor of pathology at the University of Chicago Medicine.

Fu added that "host digestion is not completely efficient, but changes in the gut flora can raise or lower digestive efficiency."

In the study, researchers used animal models to examine the relationship between gut bacteria and immune response of the body.

For the study, researchers used two sets of mice. One set of mice had a tweaked gene and lacked the ability to produce lymphotoxin- a toxin that helps the mice's immune system regulate the bacteria in the guts while the other set of mice acted as a control. Both sets of mice were fed on the same high-calorie diet.

Researchers found that both sets of mice gained during the initial weeks of the study, however, mice that lacked lymphotoxin stopped gaining weight after a couple of weeks whereas normal mice kept getting fatter.

In a second part of the experiment, researchers transferred some of the study mice's droppings to a set of mice that were raised in a germ-free environment (these mice had no bacteria in their gut). Mice that received droppings on study group mice that had lymphotoxin gained weight but mice that were given droppings from lymphotoxin-lacking mice didn't gain any weight.

When mice were housed together they ate some of the other mice's droppings( because mice are coprophagic meaning that they eat excreta of other mice) and gained the ability to get bacteria that are responsible for weight gain.

"Our results suggest that it may be possible to learn how to regulate these microbes in ways that could help prevent diseases associated with obesity. We now think we could inhibit the negative side effects of obesity by regulating the microbiota and perhaps manipulating the immune response," said Vaibhav Upadhyay, first author of the study.

According to the authors, there are more than 500 different types of strains of bacteria in the gut and "the precise microbes that promote such weight gain and the specific host responses that foster their growth need to be better established."

The study was published in Nature Immunology.