A new study suggests the long-held industry assumption that bisphenol-A breaks down safely in the human body is incorrect. Instead, researchers say, the body transforms the ubiquitous chemical additive into a compound that might spur obesity.

The study is the first to find that people’s bodies metabolize bisphenol-A (BPA) — a chemical found in most people and used in polycarbonate plastic, food cans and paper receipts — into something that impacts our cells and may make us fat.

The research, from Health Canada, challenges an untested assumption that our liver metabolizes BPA into a form that doesn’t impact our health.

“This shows we can’t just say things like ‘because it’s a metabolite, it means it’s not active’,” said Laura Vandenberg, an assistant professor of environmental health at the University of Massachusetts Amherst who was not involved in the study. “You have to do a study.”

People are exposed to BPA throughout the day, mostly through diet, as it can leach from canned goods and plastic storage containers into food, but also through dust and water.

Within about 6 hours of exposure, our liver metabolizes about half the concentration. Most of that — about 80 to 90 percent — is converted into a metabolite called BPA-Glucuronide, which is eventually excreted.

The Health Canada researchers treated both mouse and human cells with BPA-Glucuronide. The treated cells had a “significant increase in lipid accumulation,” according to the study results. BPA-Glucuronide is “not an inactive metabolite as previously believed but is in fact biologically active,” the Health Canada authors wrote in the study published this week in Environmental Health Perspectives.

Not all cells will accumulate lipids, said Thomas Zoeller, a University of Massachusetts Amherst professor who was not involved in the study. Testing whether or not cells accumulate lipids is “a very simple way of demonstrating that cells are becoming fat cells,” he said.

“Hopefully this [study] stops us from making assumptions about endocrine disrupting chemicals in general,” he said.

The liver is our body’s filter, but it doesn’t always neutralize harmful compounds. “Metabolism’s purpose isn’t necessarily a cleaning process. The liver just takes nasty things and turns them into a form we can get out of our body,” Vandenberg said.

BPA already has been linked to obesity in both human and animal studies. The associations are especially prevalent for children exposed while they’re developing.