Scientists were hoping FGF21 would be a key to lots of metabolic disorders, including diabetes. So this whole “rapid bone loss” thing is a setback for big pharma (Eli Lilly scientists published one of the first papers on FGF21, back in 2005), but also a setback for drug treatment of metabolic problems in general. That these problems are thorny is no surprise — glucose metabolism is how our cells run, after all, and its no surprise that it’s linked with many organ systems. Just as FGF21 was getting big, scientists were discovering that bones could have a role in regulating blood sugar and fat — so the bone link in the new study shouldn’t be a complete shock. What it should be is a reminder that developing drugs to change the way the body handles fat and sugar is fucking difficult — and when a company says they’ve got one, some healthy skepticism is in order.