I think there are two conversations going on here
1) can you eat a pound of something and immediately gain more than a pound (which I believe everyone agrees is just not possible)
2) If you eat a pound of certain foods, it will it add more than a pound to your overall “long term” weight
I don’t see how #2 can be possible either.
It’s been a while since I’ve been in a biology class but I seem to remember the rule of thumb we were giving is that 10 pounds of eat-ee gets you one pound of eat-er (advanced scientific terminology there), this was used whether you’re feeding hay to cows, plankton to krill, or buffalo to wolves (see Food Chain)
I believe the theoretical 3500 calorie pound of fat in the body must already take into account the tissue that doesn’t contribute calories because this would be significantly less than a theoretical “perfect” pound of fat (a pound is ~453 grams, 9 calories per gram = ~4100 calories).
So if we can assume for the sake of argument that
1) the MOST calories you can get out of a pound of food is 4100 – which is a great stretch, I don’t even think drinking olive oil straight would get ya there
2) The leftovers will be stored as fat (muscle, organs, and other tissues are going to take a lot more energy to build)
3) At least 80% of those calories are going to be burned, passed, or wasted in some way (generally this is 90%, doubling the retained portion for arguments sake)
4) We’d need ~3500 calories left over to build a pound
4100 – 80% = 820 calories left or about 91 grams of fat on your body. You would need to store three times the weight of the actual fat in water and other goodies to gain your pound from eating an ultra dense brick of fat. I just don’t believe it’s going to happen.
Even if your metabolism is extremely slow I don’t believe you could pass food and retain 50% of the calories, which would still mean about half the weight gained from the densest pound possible would need to come from sources outside the actual meal.
I’d love to be proven wrong if someone sees holes in the assumptions, I find this stuff interesting.
Also, I think the most interesting thing is the (apparently widely held) perception that four quarter pound patties are going to make you balloon up when really I think it’s just having an excess of calories each day that contributes to weight gain.