Bioavailability
The proportion of a nutrient that is actually absorbed and usable by the body after eating, depending on its chemical form and the digestive context.
Bioavailability is not just « how much of a nutrient is in the food » but « how much the body can actually use ».
Examples:
- Iron: haem iron (meat) has a bioavailability of about 20%, non-haem iron (plants) about 5%. But eating iron with vitamin C increases absorption, while eating iron with coffee or tea reduces it drastically
- Beta-carotene: raw food = poor absorption (protected by cell walls). The same food cooked and eaten with fat = absorption multiplied by 5-10
- Lycopene (tomatoes): raw = little available. Cooked tomatoes with olive oil = optimal absorption
A fresh angle: bioavailability explains why some supplements are ineffective: an iron tablet without vitamin C, taken with coffee on a full stomach, means almost zero absorption.
It is also why cooking is not the enemy and is often an ally. A dangerous myth is eating everything raw to « preserve nutrients ». Often, cooking makes those nutrients more accessible.
One last point: microbiome diversity affects bioavailability. A damaged microbiome (dysbiosis) absorbs nutrients poorly even when intake is sufficient. This is often forgotten when supplementing.