Updated

Even the wrappers at burger joints are fattening.

Fast-food wrappers contain chemicals known as perfluoroalkyl substances (PFASs for short) — and exposure to them appears to slow down the metabolism, according to new research out of Harvard’s School of Public Health.

Slow metabolism can lead to weight gain — and can also get in the way of weight loss.

PFASs are used in everything from clothing fabrics to cookware surfaces. In fast-food wrappers, they prevent leakage — say, to prevent grease from soaking through a fish fillet wrapper’s surface, making consumers all too aware of what they’re about to eat.

But according to the Daily Mail, “The chemicals can permeate into the food . . . and are then ingested and absorbed into the blood stream.”

Lead study researcher Qi Sun says that the study found a “clear link” between exposure to PFASs and sluggish metabolisms.

Also, the double-cheeseburgers inside the wrappers probably aren’t helping.

This article originally appeared on the New York Post.