Chemicals used to make products such as non-stick kitchen pans have been linked to obesity in a new study.

Researchers at Harvard believe that perfluoroalkyl substances (PFASs) in the bloodstream could disturb how the body regulates weight by lowering the resting metabolic rate. That means the body burning calories more slowly than average, meaning a person needs to eat less to avoid becoming overweight.

Past studies have linked the chemicals referred to as "obesogens" with excess weight gain, cancer, high cholesterol, immune disorders, and obesity in animals.

"Now, for the first time, our findings have revealed a novel pathway through which PFASs might interfere with human body weight regulation and thus contribute to the obesity epidemic," said senior author Qi Sun, assistant professor in the Department of Nutrition at Harvard Chan School and author of the study published in the journal Plos Medicine.

To arrive at their conclusions, researchers assessed data from 621 overweight and obese participants who took part in clinical trial investigating weight loss diets in the mid-2000s. The researchers found that those who regained the most weight after quitting the diets had lower resting metabolic rates and the highest concentrations of PFASs in their blood. Women in particular appeared to be most affected.

"We typically think about PFASs in terms of rare health problems like cancer, but it appears they are also playing a role in obesity, a major health problem facing millions around the globe," said study co-author Philippe Grandjean, adjunct professor of environmental health at Harvard Chan School.

"The findings suggest that avoiding or reducing PFASs exposure may help people maintain a stable body weight after they successfully lose some weight, especially for women."

What are PFASs used for?

For over six decades, PFASs have been used to make products including cookware, upholstered furniture and carpets, shoes, and mattresses. They are also used on airfields and other sites at risk of petrol fires, according to the US Environmental Protection Agency, as well as in heavy machinery to reduce friction.

Research has shown that such chemicals have also seeped into the water near industrial sites, military bases and water treatment plants. As they are not biodegradable, PFASs can linger in the body for a long time.

How easy is it to avoid them?

Due to their widespread use and the fact they are not broken down by air, water or sunlight, it is likely most people have come into low-level contact with PFASs, according to the EPA.

A separate study at Harvard in 2016 found that over 16m Americans drink water contaminated with PFASs.

In recent years, manufacturers have looked towards replacing PFASs with plant-based chemicals, HuffPost reported.

Should we be worried?

In 2015, over 200 scientists from 38 different countries signed a document known as the Madrid Statement, which warned of the potentially harmful effects of PFASs.

However, Alan Boobis, professor of toxicology at Imperial College, London, told The Guardian that further research was needed to make a causal link between PFASs and weight gain.

"As the authors point out, there is the potential that at least some of the findings are due to chance. The findings can serve as a good basis for further, more focused investigations into a possible link between exposure to PFASs and weight management," he said.