If Atkins is a high fat diet, why is it I have to run to the bathroom for hours after having a high fat meal at a restaurant?

Nothing I cook makes me run to the bathroom (I'm speaking of the runs)
But it never fails when I hit Red Lobster and have shrimp scampi or go to a mongolian bbq I'm stuck in the bathroom for hours upon the conclusion of the meal.

Is it just me? Do I just have a delicate constitution?