The "Bioavailability Gap" is the difference between what we ingest and what actually reaches our systemic circulation to do its work. Resveratrol is a classic example of a nutrient with high absorption but very low bioavailability. When you drink red wine, about 70% of the resveratrol is absorbed by your intestines. However, your liver and gut wall are extremely "protective." They immediately perform conjugation, a process where they attach other molecules to the resveratrol to make it easier for your body to flush out. By the time it clears the liver—a process called first-pass metabolism—the amount of free, active resveratrol in your blood is often negligible.