What Bioavailability Actually Means

By: Marcy Schoenborn

Bioavailability refers to:

The percentage of a nutrient that is absorbed and used by the body after digestion.

It is not simply how much of a nutrient is present in food.
It is how much the body can liberate, absorb, transport, and utilize.

For example:

• Spinach contains iron.

• But only a portion of that iron is absorbed.

So the bioavailability of that iron is lower than the total iron listed in the nutrition panel.

Bioavailability is influenced by several factors:

• the food matrix
• digestive enzymes
• gut microbiome
• nutrient interactions
• cooking methods
• individual metabolic health

It is never a single static number.

Why the Term Gets Abused

In some carnivore-leaning discussions, bioavailability is often used as a blanket argument like this:

“Plant foods aren’t bioavailable. Animal foods are.”

That is an oversimplification and in many cases flatly incorrect.

There are several reasons.

1. Bioavailability Is Nutrient-Specific

Bioavailability changes depending on the nutrient.

For example:

Iron

Animal foods contain heme iron, which is absorbed more efficiently.

Absorption rates:

• Heme iron: ~15–35%

• Plant iron (non-heme): ~2–20%

So yes, animal iron is often absorbed more easily.

But that does not make plant foods poor foods.

Why?

Plant foods often contain:

• vitamin C
• organic acids
• polyphenols

These compounds can increase non-heme iron absorption dramatically.

Example:

Add lemon or peppers to lentils → absorption rises significantly.

2. The Body Regulates Absorption

The human body actively regulates nutrient absorption.

When iron stores are low, absorption increases.
When iron stores are high, absorption decreases.

This is controlled by the hormone hepcidin.

So claiming a food is superior simply because its iron is absorbed more easily ignores biological regulation.

3. Fiber and Polyphenols Are Not Meant to Be Fully Absorbed

Another misuse of the bioavailability argument is saying:

“Plants contain anti-nutrients that block absorption.”

Compounds often blamed include:

• phytates
• oxalates
• tannins
• lectins

But many of these compounds are protective phytochemicals, not purely inhibitors.

Example:

Polyphenols in plants:

• feed beneficial gut bacteria
• reduce oxidative stress
• influence glucose metabolism
• regulate inflammation

These compounds often work through the microbiome, not direct absorption.

So judging plant foods by the same rules as isolated nutrients misses their biological role.

4. The Food Matrix Matters

Foods are not just nutrient containers.

They exist within a matrix of interacting compounds.

For example, legumes contain:

• fiber
• resistant starch
• polyphenols
• minerals
• amino acids

Even if one nutrient has lower absorption, the total metabolic effect of the food can be extremely beneficial.

This is why populations eating plant-forward diets often show improvements in:

• insulin sensitivity
• cardiovascular health
• microbiome diversity
• metabolic flexibility

5. Absorption Is Not the Same as Health Outcome

This is one of the biggest logical mistakes in the bioavailability debate.

Higher absorption of a nutrient does not automatically equal better health outcomes.

Example:

Animal foods provide highly absorbable saturated fat.

But high intake of saturated fat can increase:

• LDL particle concentration
• hepatic fat accumulation
• insulin resistance in susceptible individuals

So bioavailability alone cannot determine dietary quality.

6. Many Plant Nutrients Are Extremely Bioavailable

Some nutrients are very well absorbed from plant foods, including:

• potassium
• vitamin C
• folate
• magnesium
• carotenoids (especially when cooked)

For example:

Carotenoids in cooked carrots or sweet potatoes are highly bioavailable, especially when consumed with a small amount of fat.

7. Gut Microbes Unlock Nutrients

Many plant compounds become more bioavailable after microbial metabolism.

The gut microbiome converts plant polyphenols into:

• urolithins
• phenolic acids
• anti-inflammatory metabolites

These compounds influence:

• mitochondrial function
• inflammation
• vascular health
• metabolic signaling

So plant nutrients may not be immediately absorbed, but they become bioactive through microbial processing.

The Real Takeaway

Bioavailability is not a simple scoreboard where animal foods win and plant foods lose.

Nutrition is far more complex.

A better framework is:

Absorption + metabolic effect + microbiome interaction + long-term outcomes

Foods that support metabolic signaling, gut health, and cellular function tend to perform well in the long run.

And those foods are usually diverse, minimally processed, and plant-forward rather than restricted to a single category.

The Simple Way to Understand This

“Bioavailability just means how much of a nutrient the body absorbs and uses.
But some people misuse the term to make it sound like plant foods are inferior.
In reality, many plant foods are extremely valuable because they work through the microbiome, fiber, and metabolic signaling — not just direct absorption.”

 

References

Hurrell, R., & Egli, I. (2010). Iron bioavailability and dietary reference values. American Journal of Clinical Nutrition, 91(5).

Gibson, R. S., et al. (2018). Dietary strategies to improve micronutrient bioavailability. Nutrition Reviews.

Slavin, J. (2013). Fiber and prebiotics: mechanisms and health benefits. Nutrients.

Tapsell, L. C., et al. (2016). Food matrix effects on nutrient bioavailability. Nutrition Reviews.

Koh, A., et al. (2016). From dietary fiber to host physiology: short-chain fatty acids as key bacterial metabolites. Cell.