The Concept of Bioavailability
Bioavailability refers to the proportion of a nutrient consumed in food that is absorbed and available for physiological use. Not all nutrients consumed are absorbed in equal amounts. The bioavailability of a nutrient depends on multiple interconnected factors.
Nutrient Form and Chemical Structure
Nutrients exist in different chemical forms depending on their source. Iron from animal sources (heme iron) is absorbed more efficiently than iron from plant sources (non-heme iron). Vitamin forms differ in their bioavailability; for example, different forms of vitamin E have different absorption rates.
The digestibility of the food matrix affects nutrient availability. Proteins in whole foods are bound within cellular structures that affect their availability for absorption.
Presence of Other Nutrients
Nutrient interactions significantly affect bioavailability. Vitamin C enhances the absorption of iron from plant-based sources. Fat enhances the absorption of fat-soluble vitamins (A, D, E, K). Calcium and iron compete for absorption and excessive amounts of one can inhibit absorption of the other.
Phytic acid and tannins, compounds found in plant foods, can inhibit mineral absorption. However, fermentation and soaking can reduce these compounds, improving bioavailability.
Food Preparation Methods
Cooking and preparation methods affect nutrient content and bioavailability. Heat can increase bioavailability of some nutrients (such as lycopene in tomatoes) while reducing others (such as some B vitamins). Fermentation can increase bioavailability of certain minerals.
Grinding or processing can increase surface area available for digestion, potentially improving nutrient absorption. Conversely, some processing methods may reduce nutrient content.
