Factors Present in Some Foods That Decrease the Bioavailability of Particular Minerals

November 24, 2025 •

4 min read

According to research published by Harvard's T.H. Chan School of Public Health, compounds known as antinutrients are naturally present in many plant-based foods and can interfere with the body's ability to absorb essential micronutrients. This article explores which factors present in some foods can decrease the bioavailability of particular minerals, shedding light on how they work and what you can do to mitigate their effects.

Quick Summary

This article explains how certain plant compounds, known as antinutrients, inhibit the absorption of dietary minerals. It covers key factors like phytates, oxalates, and tannins, detailing their mechanisms and discussing methods to minimize their impact through food preparation techniques.

Key Points

Phytates Reduce Mineral Absorption: Phytic acid in grains, nuts, and legumes forms insoluble complexes with iron, zinc, and calcium, limiting their bioavailability.
Oxalates Inhibit Calcium and Iron: Oxalates in greens like spinach bind with calcium and iron, creating crystals that the body cannot absorb.
Tannins Affect Iron Absorption: Tannins in tea, coffee, and legumes can significantly decrease the absorption of non-heme iron.
Soaking and Sprouting Help: Traditional preparation methods like soaking and sprouting can break down antinutrients like phytates and lectins, improving mineral access.
Cooking Reduces Inhibitors: Boiling and other thermal processing can deactivate antinutrients, though some minerals may be lost in the cooking water.
Pairing Foods Maximizes Absorption: Consuming foods rich in vitamin C with iron-rich foods, or calcium with oxalate-rich foods, can enhance mineral uptake.
Diverse Diets Mitigate Effects: A balanced and varied diet naturally offsets the impact of antinutrients, as beneficial compounds can counter inhibitory ones.

The availability of minerals from food is a complex process influenced by a variety of dietary components. While many plant-based foods are excellent sources of nutrients, they also contain compounds that can bind to minerals in the digestive tract, reducing the amount the body can absorb. Understanding these factors, known as antinutrients, is key to maximizing nutritional intake.

The Role of Phytates (Phytic Acid)

Phytates, or phytic acid, are common antinutrients found primarily in the hulls of nuts, seeds, and grains, as well as legumes. They serve as the primary storage form of phosphorus in these plant foods. The problem for humans is that our digestive tract lacks sufficient quantities of the enzyme phytase, which is needed to break down phytic acid. As a result, phytic acid readily binds with minerals like zinc, iron, magnesium, and calcium to form insoluble complexes, making them unavailable for absorption.

To counter the effects of phytates, traditional food preparation methods have proven effective:

Soaking: Soaking legumes and grains overnight in water and then discarding the water can significantly reduce phytate levels.
Sprouting: Also known as germination, sprouting can trigger the breakdown of phytic acid by activating intrinsic phytase enzymes in the plant.
Fermentation: The fermentation process, such as in making sourdough bread, can effectively degrade phytates and other antinutrients.

The Impact of Oxalates (Oxalic Acid)

Oxalates are organic compounds found in many plants, with particularly high concentrations in leafy greens like spinach, rhubarb, and beet greens. When consumed, oxalates can bind with calcium and iron to form insoluble crystals, preventing their absorption. While a standard diet doesn't pose a significant risk, a high oxalate intake can be problematic for those with deficiencies or conditions like kidney stones.

Mitigating oxalate content can be achieved through simple cooking methods:

Boiling: Boiling vegetables high in oxalates and discarding the water is an effective way to remove a significant portion of the compound.
Steaming: While less effective than boiling, steaming can still reduce oxalate levels while preserving more water-soluble vitamins.
Pairing with Calcium: Consuming a calcium-rich food, like dairy, alongside an oxalate-rich food encourages the binding of oxalates to calcium in the stomach rather than in the kidneys.

The Effect of Tannins

Tannins are polyphenolic compounds found in various plant-based foods and beverages, including tea, coffee, legumes, and certain fruits. They are known for their astringent taste and ability to precipitate proteins and chelate minerals. The primary mineral affected by tannins is iron, particularly non-heme iron found in plant foods. Tannins can reduce the absorption of iron by forming unabsorbable complexes.

Tips for reducing the inhibitory effect of tannins:

Time Your Beverages: Avoid drinking tea or coffee with meals, especially those rich in iron. Instead, consume them between meals.
Peeling: For foods like nuts and legumes, peeling the skins can significantly reduce the tannin content.

Comparison of Antinutrient Effects on Mineral Bioavailability

To better understand the distinct impacts of these factors, consider the following comparison table:


Antinutrient	Primary Food Sources	Primary Minerals Affected	Mechanism of Action	Mitigation Strategies
Phytates (Phytic Acid)	Whole grains, legumes, seeds, nuts	Iron, Zinc, Calcium, Magnesium	Chelates (binds) to minerals, forming insoluble salts.	Soaking, sprouting, fermentation.
Oxalates (Oxalic Acid)	Leafy greens (spinach, chard), rhubarb, beets	Calcium, Iron	Binds to minerals to form insoluble crystals.	Boiling, steaming, consuming with calcium-rich foods.
Tannins (Polyphenols)	Tea, coffee, grapes, legumes, nuts	Iron (non-heme), Calcium, Zinc	Binds to and precipitates proteins and minerals.	Separating consumption from mineral-rich meals, peeling.
Lectins	Legumes (beans, peanuts), grains	Calcium, Iron, Zinc	Binds to cells in the digestive tract, potentially hindering absorption.	Proper cooking (especially boiling) and soaking.

Conclusion

While antinutrients can reduce the absorption of certain minerals, it's important to remember that the foods containing them are also packed with essential vitamins, minerals, and fiber. For most people with a varied and balanced diet, these compounds are not a significant health concern. However, those at risk of mineral deficiencies or who rely heavily on plant-based staples may benefit from intentional food preparation strategies. Cooking, soaking, and fermentation are simple, traditional techniques that effectively reduce antinutrient levels and improve the bioavailability of key minerals, allowing you to get the most nutritional value from your food. The ultimate goal is to balance the diet and use preparation methods to maximize mineral absorption rather than avoiding healthy plant foods altogether. For further reading on the effects of tannins, explore research in medical literature.

A Note on Dietary Balance

The impact of antinutrients is also dependent on a person's overall dietary pattern and individual health status. For example, studies suggest that vitamin C can counteract the inhibitory effect of phytates and tannins on iron absorption. Similarly, vitamin D is crucial for calcium absorption, regardless of dietary phytate levels. By focusing on a diverse diet rich in vitamins and minerals, the negative effects of antinutrients can be significantly minimized. It is the overall dietary context that determines the net absorption of minerals, not just the presence of a single inhibitory compound.

Frequently Asked Questions

Antinutrients are natural or synthetic compounds found in various foods, especially plants like legumes, grains, nuts, and seeds. They interfere with the absorption of essential nutrients such as vitamins and minerals.

No, soaking does not remove all antinutrients, but it can significantly reduce the levels of water-soluble compounds like phytates and lectins. Discarding the soaking water and rinsing thoroughly are important steps.

Yes, you can improve iron absorption by pairing iron-rich plant foods with foods high in vitamin C, which helps convert non-heme iron into a more absorbable form.

For most people with a varied diet, oxalates are not a major concern. However, those prone to kidney stones or with mineral deficiencies may need to be mindful. Boiling high-oxalate greens and pairing them with calcium can help reduce oxalate absorption.

Fermentation uses microorganisms to break down carbohydrates and other compounds, including antinutrients like phytates and lectins. This process can significantly reduce antinutrient levels and improve mineral bioavailability.

No, the inhibitory effect of tannins depends on their concentration and the specific type. For instance, more mature wines have less astringent (tannin) effects than unripe fruits. The impact can also depend on when the food is consumed relative to mineral-rich foods.

Excessive intake of certain types of fiber, particularly those associated with phytates, can reduce the absorption of some minerals. However, soluble fibers may improve absorption in some cases by creating a favorable gut environment. A balanced approach is key.