How much of what we eat counts?

For RNYers, how much of what we eat gets absorbed or counts?  I keep reading about the importance of nutrition during pregnancy and how we must get nutrients from food as well as prenatal.  I try to eat a couple of servings of fruit per day as well as drinking milk a couple of times and I wonder how much if any is helping support the baby.

For 18 months...you absorb half of what you eat. After 18 months, it inches back up to you absorbing almost all of foods or fat.
You will always malabsorb half of your vitamins & calcium. You can never absorb B12 without it being a sublingual, nose spray, or shot.
Hope this helps.