Initially my surgeon said to me that if I am gaining weight than I am absorbing...That was the 70's and we have come a long way since.
I used to juice including major mineral-rich foods like parsley, cilantro and other herbs now I just blend...don't bother throwing away all of the goodness (and it slows digestion to allow me to absorb a bit more).
Some things are absorbed through our stomachs (not many) like sugars, alcohol and certain meds but most foods absorb through our small bowels. Most foods were not meant to stick around that long in them so we technically should have enough gut leftover to absorb most elements.
The micronutrients are another story. Most people these days do not get enough of them and processed foods and industrial farming deprive us of most of these elements.
Supplements are essential. But not for all of us.
I just did a 30 day run of magnesium, copper/gold/silver, cobalt/zinc/selenium...I haven't slept so well since I started taking it. It took it 2 days to kick in and I have had over 2 months of uninterrupted sleep cycles. I fought off a nasty lung bug in a week and have been the Eveready bunny for weeks.
I finished the treatment 5 days ago.
I am exhausted again. So maybe I needed it more than I thought.
My old GP used to set me up, 4xs/yr, with a micronutrient regimen to get me through the seasons. It worked wonders.
A good naturopath or nutritionist can help make you up a list and they can test your hair to see what is missing.
Sharon