What is excreted in diarrhea?

Question

When you have diarrhea, what portions of the food is excreted? Does only the poisoned portions become excreted or do the whole stomach contents get excreted?

Here is a practical example: For your post workout shake, you blend whey protein with milk. You did not know the milk was expired. After drinking the shake, you get a stomach ache and have diarrhea. What exactly was excreted in the diarhea? Did only the milk get excreted and not the whey? Or did both get excreted? In the latter case, one would need to eat more protein, but in the former case, you don't need to worry because the protein is still in your system.

Answer 1

I'm not a medical professional, but this is how I understand it:

Infectious diarrhea (e.g. from food poisoning) is your body's reaction to certain bacteria in the bad milk you had. Diarrhea simply means that your bowels are working unusually fast, so there is no time for the usual processing, hence the liquid form. This makes sense because your body wants to get out the bacteria as fast as possible, so they can't do as much damage.

Bad milk is simply milk (with proteins and all) plus bacteria. Once you mix the milk with something else, it doesn't matter whether the milk was bad or whatever you mixed it with: The bacteria simply end up everywhere, they are not somehow tied to the milk's nutrients.

In response to the bacteria your bowels "fast-track" the entire load of food they have inside them, which means less of it will be absorbed by your body (because there is less time). This affects all nutrients the same way, your bowels has no reason to distinguish between them since the nutrients are separate from the bacteria. So the bad milk is not completely excreted and the rest is not completely absorbed, both are absorbed to the same extent but that extent is less than usual.