How do we know how much food nutrients are actually absorbed by the human body?

Question

I know there are chemical processes to detect the quantity of nutrients in food but how do we know how much of these nutrients are actually absorbed by the human body? How much variance is there between different people?

In: 27

Answer 1

We had people fast, then did bloodwork to see how many nutrients are in their body when they haven’t eaten for a long time.

Then we fed them the stuff we wanted to test out. We took more bloodwork several times over the day to see how the nutrients in their bloodstream changed with respect to the time since they had eaten.

We did that for hundreds and thousands of people and built up a pretty good model.