Bioavailability

Bioavailability is the proportion of a nutrient that is digested, absorbed, and utilized by the body. A food may contain 100mg of iron, but if only 5% is bioavailable, your body receives just 5mg. This is why spinach, despite containing significant iron, is not an efficient iron source—its oxalic acid binds iron into insoluble complexes that pass through the gut unabsorbed. Bioavailability depends on the nutrient's chemical form, the food matrix, the presence of enhancers or inhibitors, gut health, and individual variation. It's not what you eat that matters—it's what you absorb.