Sometimes when you're at the dinner table, it feels like you're under siege.

First comes a battalion of bread sticks. A brisket leaps into the breach. Then, the mashed potatoes are coming! The mashed potatoes are coming!

The main course arrives — a ham or roast or turkey flanked by cranberries and gravy and a constellation of carrots, cauliflower and corn.

Mercy, your belly pleads.

And finally, your aunt appears in the doorway resplendent in a gravy-smeared apron. She bears the piece de resistance. Pumpkin pie crowned with a cloud of whip cream.

The thing is, no matter how your belly moans — no matter how hard you strain to stave off the looming food coma — that pie is actually the piece de no resistance.

You simply can't say no.

Why is that? Why do we always find room for that belly-busting pie?

Science suggests it's no Christmas miracle. In fact, research published in the Journal of the Norwegian Medical Association points to a simple reason why, when it comes to your stomach, there's always room at the inn. Your belly doesn't bust. It bends.

And sugar — the stuff traditionally dumped wholesale in pies and pastries — acts as a trigger for expanding that organ to meet fresh, err… challenges.

Your brain equates fullness with stomach pressure. But sugar, or more specifically glucose, tells the brain to loosen the stomach walls. That relieves some of the pressure in your belly, while allowing more food to be piled inside — namely sweets.

"If you eat dessert after you're actually feeling stuffed you're tricking your normal sensation of being full," the researchers noted in Science Norway. In fact, there's even a name for this situation, aptly called dessert stomach.

But that's not the only reason why there's always room for dessert. For all the various plates of food that parade past the holiday table, it can add up to "sensory-specific satiety," defined as a "temporary decline in pleasure derived from consuming a certain food in comparison to other unconsumed foods."

Put simply, foods with similar tastes and textures bore the senses. Introduce a lemon meringue pie in all its technicolor glory, and you may suddenly find an opening for it.

A brain with a doughnut inside. You can't trust a sugar-addled mind. (Photo: canbedone/Shutterstock)

But when it comes to overeating — and packing on all those extra holiday pounds — the "sugar reflex" could be most dangerous.

"The problem is that you don't know when to stop eating dessert," added study author Arnold Berstad.

It could also — if used judiciously — be a method for easing discomfort from a heavy meal. The key, the researchers suggest, is limiting dessert to just a taste.

That way the stomach walls slacken, giving you a little breathing room, without immediately being stuffed full of pumpkin pie.

Of course, for anyone who's ever come face to face with homemade pumpkin pie, resistance may be futile.

This is why you always have room for dessert
You may think you're stuffed, but sugar has a way of making more space in your stomach, Norwegian researchers discover.