This year, call their bluff by holding a barbecue relay. Anyone who wants a meal is required to participate. Explain that the relay works off at least some of the calories they’re about to consume.
Set up rows of barbecue tools about 100 yards apart, or 100 meters if you’re in Canada, eh. Place the pointy sides up, as in the photo. Unlike the photo, don’t skewer uncooked meat unless your guests are really into the raw foods thing — and be sure to get a signed waiver from those wackos in case they develop parasites.
Line up nine guests at a time. When you blow a whistle, they must sprint/run/waddle to the opposite set of tools, grab whatever meat they want, and return to their starting tool line. Only the first, second and third finishers get to keep their entree. Others must wait until a later heat to try again.
Serve your salads and pasta dishes in the same manner. By then, everyone will be so tired you can probably get by with half the usual amount of food.