A nutrient has to clear four obstacles to work: it must survive digestion, dissolve, cross the intestinal wall, and be delivered to your cells. Delivery technologies like liposomes exist to help nutrients get past one or more of these barriers — which is why the same nutrient in two formats can absorb very differently.
The four barriers
1. The digestive gauntlet
Stomach acid and enzymes are built to break things down. Fragile compounds — certain antioxidants, sensitive peptides, some forms of vitamin C — can be partly destroyed here before absorption begins.
2. The solubility problem
Many valuable compounds are fat-soluble (curcumin, CoQ10, resveratrol) and dissolve poorly in the watery environment of the gut. If a compound won't dissolve, it largely won't absorb, no matter the dose on the label.
3. The intestinal wall
The gut lining is selective. Some nutrients cross easily through dedicated transport systems; others are actively pumped back out or simply pass through unabsorbed.
4. Delivery to the cell
Reaching the blood isn't the finish line. The nutrient still has to be delivered to and taken up by cells — the stage that gives cellular absorption its name, and the one most marketing quietly skips.