A new study is challenging the popular belief that smoking cigarettes help people keep off extra pounds.

Researchers at Brigham Young University found that exposure to cigarettes smoke can actually cause weight gain. But here's the kicker: Secondhand smoke may be the biggest culprit.

Data shows half of the U.S. population is exposed at least once daily to secondhand cigarette smoke and approximately 20 percent of young children live with someone who smokes in the home. Every day, nearly 4,000 young adults smoke their first cigarette and 1,000 become habitual smokers.

"For people who are in a home with a smoker, particularly children, the increased risk of cardiovascular or metabolic problems is massive," Benjamin Bikman, an author of the study and a professor of physiology and developmental biology at Brigham Young University, said in a statement.

For the study, Bikman and his colleagues exposed lab mice to secondhand smoke and followed their metabolic progression.

They found that those exposed to smoke put on weight. When they drilled down to the cellular level, they found the smoke triggered a tiny lipid called ceramide to alter mitochrondia in the cells, causing disruption to normal cell function and inhibiting the cells' ability to respond to insulin.

"The lungs provide a vast interface with our environment and this research shows that a response to involuntary smoking includes altering systemic sensitivity to insulin," researchers Paul Reynolds said in a statement. "Once someone becomes insulin resistant, their body needs more insulin. And any time you have insulin go up, you have fat being made in the body."

Researchers said the key to reversing the effects of cigarettes smoke is to inhibit ceramide. They found that the mice treated with myriocin (a known ceramide blocker) didn't gain weight or experience metabolic problems, regardless of their exposure to the smoke. However, when the smoke-exposed mice were also fed a high-sugar diet, the metabolic disruption could not be fixed.

Now Bikman and his team are in a race with other researchers to find a ceramide inhibitor that is safe for humans.

"The idea that there might be some therapy we could give to innocent bystanders to help protect them from the consequences of being raised in a home with a smoker is quite gratifying," Bikman said.

The findings are detailed in the American Journal of Physiology: Endocrinology and Metabolism.