"I don't think with my stomach, I just don't process well when it's empty." Which was a mild exaggeration, but close enough. Hansel got very grumpy when underfed.
He probably wouldn't have believed her though, she was right there. She'd have gotten a scoff and he'd have told her to stop making shit up just because. But then and now, well, he had a stomach to attempt to fill.
He wasn't even bothered about over filling right then, he'd worry later. If it happened to be the greasiest food he ever touched in his lifetime, well fine. Candy hadn't killed him, grease wouldn't either.