Adolescents exposed to toxic “forever chemicals” may be more likely to regain weight lost after bariatric surgery, a new study has found.

The risk of such gains, which can undermine the procedure’s success and cause long-term health issues, was higher in patients who had elevated levels of the compounds prior to the surgery, scientists found in the study, published on Thursday in Obesity.

These so-called forever chemicals, or per- and polyfluoroalkyl substances (PFAS), are notorious for their ability to persist in both the human body and the environment.

Linked to numerous cancers and serious health conditions, PFAS are present in certain firefighting foams and a variety of household items, including nonstick pans, cosmetics and waterproof apparel.

Bariatric surgery, a procedure that alters the digestive system, has long been used as a treatment for severe obesity, with the goals of reducing risks of type 2 diabetes and cardiovascular disease, the study authors noted.

Yet with so many individuals regaining the weight over time, the researchers sought out answers as to why those setbacks might occur.

They said they were particularly curious about the role PFAS exposure might play, since the compounds are known to interfere with metabolic processes.

Several studies, they explained, have already documented such effects in adult populations, but the extent to which those impacts apply to teenagers remains unclear.

“With the growing use of weight loss interventions around the world, it’s critical for us to understand the association between PFAS and successful weight loss management,” lead author Brittney Baumert, a postdoctoral fellow at the University of Southern California’s Keck School of Medicine, said in a statement.

Baumert and her colleagues tracked 186 adolescents from the Teen-Longitudinal Assessment of Bariatric Surgery (Teen-LABS) study — a national initiative funded by the National Institutes of Health — who underwent bariatric surgery between 2007 and 2012.

Teen-LABS researchers measured blood levels for seven types of PFAS in each patient before surgery, as well as weight, body mass index and waist circumference before the procedure and six months, one year, three years and five years later.

Baumert and her co-authors harnessed the data from Teen-LABS and divided the adolescents into low, medium and high PFAS exposure groups. They then compared the weight gain and waist expansion outcomes among the cohorts and for each kind of PFAS.

Ultimately, the scientists found that patients with higher blood levels of three types of PFAS — PFOS, PFHxS and PFHpS — exhibited greater weight gain and increases in waist circumference in the one to five years following surgery.

Regarding PFOS specifically, adolescents in the low exposure group with starting body weights of 328 pounds or more regained an average of 35.9 pounds by the five-year mark, the researchers observed. Teens of the same starting weight with the highest PFOS levels gained about 46.9 pounds.

For PFHpS, patients in the lowest exposure group regained about 2.7 of their baseline body weight each year, while those in the highest cohort regained an average of 4.3 percent on average, per the study.

The authors expressed hope that their findings could help inform strategies for improving patient care. Since bariatric surgery is invasive and expensive, they stressed the importance of understanding who the procedure could truly benefit.

In the future, Baumert said she is interested in exploring whether PFAS exposure influences any other weight loss interventions, including the function of GLP-1 medications like Ozempic.

She and her team also noted that the study adds to an expanding body of research that could steer policymakers toward stronger regulation of PFAS, particularly in public water supplies.

“PFAS are a modifiable risk, which is why protective policies are so important to reduce exposure and safeguard public health — especially for vulnerable populations,” Baumert added.