I eat a small meal before I go to social events, so that I can honestly say "No thanks, I'm not hungry." But I leave a little wiggle room in my calorie budget for a couple hors doeuvres, and a few bites of dessert. Remember, the first couple bites are the best part anyway. I drink sparkling water, unsweetened iced tea or diet pop all night. A little lemon twist goes great with any of those, and makes it look less like you're teetotalling which always seems to beg discussion.
Sometimes, if I know that I'm really looking forward to one of the items to be served, or it would look strange for me not to be eating (like dinner out with friends), I just eat a very light breakfast and salad for lunch, then have a third or half portion of dinner at my event.
The hard part is that every event is different, and will require different strategies for navigation without calling attention to yourself. If you don't make a point of saying "Oh, I can't eat that!" every time you see a platter, chances are nobody is paying enough attention to what you're eating to comment on it.