Most of the students were in their first or second year on campus, and few of them were (I suspect) engineering or science majors -- it wasn't specifically an engineering- or science-related event. At a guess, I'd say that for most of them, the idea that calories can measure energy in all its forms and not just personal weight gain was a bit foreign. So the questions I got were mostly based in confusion, but some of the students were curious enough to ask. And once the units of measurement became clear, the message got through -- you can't keep spending more than you get back in return, not in the long run.
Even for the ones who didn't ask, I think I managed to create a little cognitive dissonance. They were eating free food. And they were liking the free food they were eating. And yet there was a message which seemed to imply that the food they were eating presented a problem.
Sometimes, creating even the tiniest bit of unease can stimulate a process of inquiry, and investigation, and re-thinking. For some of the students at the event, I hope I was able to discomfort them that tiny, little bit.