It’s estimated that more than a billion people smoke cigarettes despite its role in causing disease. Recent studies have shown that 70 percent of smokers are interested in quitting but are concerned that they will gain weight.

For years, the cause of weight gain as the result of quitting smoking has been unclear. In a recent study published in Nature, Weizmann Institute of Science researchers say the culprit may be weight-modulating compounds released by gut microbes.

The researchers found that mice regularly exposed to cigarette smoke failed to gain weight, despite consuming a diet high in fat and sugar. When the smoke exposure stopped, the mice rapidly gained weight. But when the mice were given broad-spectrum antibiotics that depleted their microbiome, they gained much less weight after undergoing smoking cessation, staying slim for months regardless of their diet.

Prof. Eran Elinav. Photo courtesy of the Weizmann Institute of Science

The scientists believe that smoking-related compounds such as nicotine penetrated the gut of the smoke-exposed mice, altering the gut’s bacterial composition and, consequently, the body’s metabolism.

They also assessed the microbiomes of 96 smoking and nonsmoking people. They found marked alterations in the microbiome of smokers, as well as microbial metabolite changes similar to those found in the smoke-exposed mice.

“Our findings exemplify how the host and microbiome act as partners in regulating weight and metabolism,” said immunologist Prof. Eran Elinav, who headed the research team.

“The compounds we have identified may lead to new treatments that will help people avoid weight gain when quitting smoking. Moreover, these compounds may be further developed into therapies to fight obesity even among nonsmokers.”