Bioavailability is the proportion of a nutrient that is absorbed and available for use in the body. Knowing the nutrient content of a food is only part of the picture.

Factors affecting bioavailability:

• Food matrix — nutrients in whole foods are absorbed differently than isolated supplements
• Cooking — can increase or decrease availability depending on nutrient and method
• Antinutrients — phytates, oxalates, tannins bind minerals and reduce absorption
• Nutrient interactions — vitamin C enhances iron absorption; calcium inhibits iron; fat required for fat-soluble vitamins
• Gut health — damaged intestinal lining impairs absorption
• Individual variation — genetics, age, gut microbiome affect absorption rates

Practical examples:

• Cooked carrots deliver more beta-carotene than raw
• Soaking and fermenting legumes reduces phytate content, improving mineral absorption
• Adding fat to a salad dramatically increases absorption of fat-soluble antioxidants (lycopene, beta-carotene)

Reference:

Wikipedia: Bioavailability

https://en.wikipedia.org/wiki/Bioavailability