Keck School of Medicine of USC Dec 4 2025 A new USC study shows teens with higher blood levels of per- and polyfluoroalkyl substances (PFAS) measured before bariatric surgery had smaller improvements in blood sugar over five years, including fasting glucose and hemoglobin A1c (HbA1c), which measures average blood sugar levels over the past 60-90 days. Blood sugar is a key marker of the surgery's success-and the differences were large enough that the metabolic benefits of the surgery could fade