It wasn't a food thing, exactly. Not in the beginning. It was a control thing. It escalated, though, and no matter how little he wanted to put the label of 'eating disorder' to it, it was true.
Sam was getting bad again. The past few weeks had been good, better than he'd felt in a long time. But they'd gotten back from a rough hunt, he'd made a few stupid mistakes he should have avoided, and the downward spiral started yet again. (Sam has been struggling with self-harm and self-hatred. Dean and Cas reassure him that they'll be there for him, no matter what)
"See, it's gone because it's not real. Me? I'm real. You're stuck with me. Because I'm real, Sammy." And it was true- with Dean in such close proximity, the idea of thinking any of his hallucinations were true seemed completely ridiculous.