How much food is absorbed, and how much comes out again?

Question

I always thought that most of the food comes out again after nutrients are absorbed.

For example, here is a can of noodles. It says the 800gr in the can have a total of something like 600kcal. If the entire can would be converted into fat, this would have to be about 5500 kcal. That would mean that about 90% of it comes out again.

But sometimes I eat and eat and eat and a lot less is coming out then went in.

So, how much food is actually coming out again after being processed in the body?

In: 128

Answer 1

In ecology we use the 10% rule, which says that approximately 10% of what is consumed at one tropic level is transferred to the next. So as a rule of thumb you can say approximately 10%.