Psst, don't tell anyone, but the real reason we gain weight may be that we're thinking too much. Yup, the harder our brains are working, the more food we eat, even though we're not really expending any more energy than we would be just lounging around.
So while it'd probably be in your attendees' best interests to give them a nice exercise session after a tough, mentally grinding one, they'll likely be happier with a big old pile of food. But you already knew that, didn't you? Still, it's nice to have some science to back it up.