That's right, defy your mother.  Remember when she said, "Finish that.  There's lots of kids who don't get enough to eat."  The intentions were admirable.  Don't waste food.  Think of others, etc.  Unfortunately, those starving kids are not gonna get that slice of Coconut Cream Pie that got plopped on your desk at work commemorating some innocuous birthday celebration.  Thank them for it, find a time when nobody's watching and dump it in the trash.  That's right....................WASTE IT!  You don't need it.  It's just going to end up encircling your abdomen.  DUMP IT!  If you can politely say "No thanks", obviously that's the way to go, but, as I have often seen, people are offended if you turn it down.  Our society seems to have an obsession with celebrating everything by having everyone eat a big plate full of CRAP!!   Happy Birthday!!  Eat some cake, have big scoop of ice cream on it, and how about some caramel and nuts on top of that?!!
     I'm not saying never eat cake.  I do, and there's nothing wrong with it.  I just refuse to be cornered into eating a big hunk of carbs that I didn't want in the first place, just to keep peace in the office.   The piece that I just surrepetitiously dumped in the trash was an extra 400 +- calories that I don't need today.  If you're gonna eat more, PLAN IT!  Manage the rest of your day's caloric intake so you can afford it.  It's a budget, plain and simple.  Don't take more than you can afford.  Your body uses a certain amount of energy every day, depending upon your activity level.  If you take in more, it goes to fat for use later.  If you take less, it burns off a bit of the stored energy to make up the deficit.   No hocus pocus here.  Just biology.