Bioavailability

What Is Bioavailability?

Bioavailability refers to the proportion of a nutrient that is absorbed from food and made available for use in the body's physiological functions. A nutrient present in food is not necessarily fully utilized — the body must first digest, absorb, and transport it before it can perform any biological role. Bioavailability is therefore a critical concept in nutrition science, as it determines the actual nutritional value of a food rather than just its theoretical content.

Factors That Affect Bioavailability

Many variables influence how well a nutrient is absorbed:

• Food matrix: Nutrients bound tightly within plant cell walls or protein structures may be released slowly or incompletely during digestion.
• Cooking and processing: Heat can break down cell walls and improve absorption of some nutrients (such as lycopene in tomatoes) while degrading others (such as vitamin C).
• Antinutrients: Compounds like phytates (in grains and legumes), oxalates (in spinach), and tannins (in tea) bind minerals such as iron, calcium, and zinc, reducing their absorption.
• Nutrient interactions: Vitamin C significantly enhances non-heme iron absorption, while calcium competes with iron for the same intestinal transporters.
• Physiological status: Iron-deficient individuals absorb iron more efficiently than those with adequate stores. Pregnancy also increases calcium and iron absorption.
• Gut microbiome: Certain bacteria produce short-chain fatty acids and other compounds that influence mineral transport across the intestinal lining.

Practical Implications

Understanding bioavailability helps explain why dietary recommendations differ between food sources. For example, heme iron (from meat) is absorbed at a rate of roughly 15–35%, whereas non-heme iron (from plant foods) is absorbed at only 2–20%. Similarly, calcium from dairy is more readily absorbed than calcium from some leafy greens due to the presence of oxalates. Soaking, sprouting, and fermenting grains and legumes can reduce antinutrient content and meaningfully improve mineral bioavailability. Food preparation choices therefore have a direct effect on the nutritional benefit obtained from a meal.