Herbst confirms that dropping a deuce will in fact budge the number on the scale, though it won't alter your body composition or muscle percentage, saying, "One pound in does not guarantee one [pound] out," because food is metabolized differently. Certain foods are absorbed more efficiently, while others pass right through (looking at you, corn).
So while a pound of lettuce may work its way out to the porcelain water slide, a pound of pie will most likely stick to your thighs. Pooping isn't a total elimination of all the calories you eat, since that wouldn't make any sense. Your body needs energy, so it's not going to shit it all out.
On top of that, Herbst's experience monitoring weigh-ins taught him that no one's going to see Biggest Loser-type results. He says you may see a 5lb drop (if that), depending on how much you currently weigh. If you're a big dude, you're going to expel more in weight and volume because you're already eating more.
The majority of people will only be able to look forward to a mere 1-2lb difference (at most) if you're an active person. Those losses aren’t worth canceling your gym membership, and in extreme cases, excessive laxative use can lead to all sorts of nasty medical complications.