Now researchers at the University of California, Irvine, think they know why—and no, pot consumption isn’t the secret to a svelte figure.

Not a healthy one, anyway.

Frequent cannabis consumers are leaner and less likely to develop type two diabetes. But the pseudo-health benefit comes at a price, researchers assert in a June 2 article published in Cell Metabolism.

Many cannabis consumers begin use during their teenage years. Realizing this, researchers gave low doses of THC—tetrahydrocannabinol, the main psychoactive component of marijuana—to adolescent mice. Once the mice were fully grown, they stopped the doses, but the damage was done.

Drug-free male mice that had consumed THC as “teens” had reduced fat mass, increased lean mass, had higher-than-average body temperatures, and were partially resistant to both obesity and hyperglycemia. They were in what researchers referred to as a “pseudo-lean” state.

But they also had a reduced ability to use fuel from fat stores—a consequence that can interfere with tasks like moving and thinking, and especially sustaining attention, researchers found.