Bioavailability
ˌbaɪ.oʊ.əˌveɪ.lə.ˈbɪl.ɪ.ti
The proportion of a nutrient from food or supplements that your body actually absorbs into the bloodstream and puts to use for normal body functions.
Full Explanation
Eating a nutritious meal is just the beginning of a longer journey. After the food digests and nutrients free from its physical structure, those nutrients must cross the wall of your gut, enter your bloodstream and travel to the tissues and organs where they're actually needed and used.
Bioavailability describes how much of a nutrient successfully completes that entire journey. It's the bottom line of nutrition: not just what's in your food, but what your body ultimately gets out of it.
Many things influence this, including what else you eat at the same meal, how the food was cooked or processed, your age and health status, your gut microbiome and even your genetics.
Macronutrients like fats, carbohydrates and proteins are usually highly bioavailable, about 90% +. But vitamins and minerals can vary wildly, sometimes with only a small fraction of what you eat actually reaching the parts of the body that need it.
Why It Matters
Bioavailability is the difference between what a food contains and what your body actually receives, especially when it comes to micronutrients. Two people eating same food can end up with very different nutritional outcomes based on individual differences in gut health, age or genetics. For anyone managing a nutrient deficiency, choosing supplements, following a diet regime or building a balanced diet, understanding bioavailability helps you make those decisions far more effectively.
Example
Iron from red meat (called heme iron) is more bioavailable than iron from spinach or lentils (non-heme iron). However, pairing plant-based iron sources with vitamin C, like squeezing lemon over spinach, can meaningfully improve how much iron your body absorbs and uses.
Common Misconceptions
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"More of a nutrient always means more benefit". Not necessarily, if a nutrient has low bioavailability, consuming more of it doesn't guarantee your body will absorb or use more of it.
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"Supplements are always better absorbed than food sources". It depends on the nutrient and the form; some nutrients are more bioavailable from whole foods, while others are better absorbed from certain supplement forms.