What decreases the bioavailability of minerals? Unpacking the role of anti-nutrients and diet

October 15, 2025 •

4 min read

Micronutrient malnutrition, including iron and zinc deficiencies, affects more than half the world's population, partly due to low bioavailability of minerals in plant-based diets. Understanding the factors that inhibit mineral absorption is crucial for maximizing the nutritional value of your food.

Quick Summary

Several factors reduce mineral bioavailability, most notably anti-nutrients such as phytates and oxalates found in plants, which bind to minerals and prevent absorption. Other influences include dietary interactions, specific preparation methods, and an individual's health status.

Key Points

Anti-nutrients are mineral inhibitors: Compounds like phytic acid (in grains and legumes) and oxalic acid (in spinach and rhubarb) bind to minerals, forming unabsorbable complexes.
Food preparation can boost absorption: Soaking, sprouting, and fermentation can significantly reduce anti-nutrient levels in plant foods, freeing up minerals for absorption.
Other dietary components matter: Polyphenols in coffee and tea can inhibit non-heme iron absorption, while Vitamin C can enhance it, showing that food combinations are key.
Individual factors play a role: A person's health, age, and nutrient status all influence how effectively they absorb minerals, as can gastric acid levels.
Not all minerals are equal: The bioavailability of minerals varies by their chemical form; for example, heme iron from animal sources is more readily absorbed than non-heme iron from plants.
Balance is more effective than avoidance: Rather than eliminating foods containing anti-nutrients, focus on balancing your diet and using simple preparation techniques to maximize nutrient availability.

Bioavailability is the measure of how much of a nutrient is absorbed and utilized by the body. A food may be rich in minerals, but if their bioavailability is low, the body may not be able to reap the full benefits. Many people, particularly those relying heavily on plant-based staples, may struggle with mineral deficiencies due to certain natural compounds and dietary habits. Understanding these factors is the first step toward improving your nutrient intake.

The Impact of Anti-Nutrients on Mineral Absorption

Anti-nutrients are compounds naturally found in many plant-based foods that can interfere with the absorption of essential vitamins and minerals. They are a primary reason why the bioavailability of minerals from plant sources can be lower than from animal sources.

Phytic Acid (Phytates)

Phytic acid, or phytate, is one of the most prominent anti-nutrients. It is the main storage form of phosphorus in many plants, especially seeds, legumes, and nuts. Phytic acid has a strong negative charge that readily binds with positively charged metal ions, including zinc, iron, magnesium, and calcium, forming insoluble mineral-phytate complexes in the digestive tract. These complexes are not easily broken down or absorbed by the human body, which lacks sufficient phytase, the enzyme required to degrade phytates. High-phytate diets, common in developing countries, are linked to significant mineral deficiencies. Fortunately, traditional food preparation methods can effectively reduce phytate content.

Oxalic Acid (Oxalates)

Oxalic acid and its salts, known as oxalates, are found in many leafy greens, vegetables, and legumes. Oxalates also bind to minerals, particularly calcium and, to a lesser extent, iron, forming insoluble crystals. While this is a concern for calcium absorption from foods like spinach and rhubarb, it is less of an issue for overall absorption in a balanced diet. The insoluble calcium oxalate is often excreted, and other sources of calcium in the diet can compensate. High intake of oxalates, however, can be a risk factor for kidney stones in susceptible individuals.

Polyphenols and Tannins

Polyphenols are a broad class of plant compounds with antioxidant properties. Certain types, like tannins found in tea, coffee, and some fruits, can chelate or bind with minerals like non-heme iron, copper, and zinc. The binding of polyphenols to non-heme iron is especially pronounced, significantly inhibiting its absorption. This effect is dose-dependent, meaning a greater concentration of polyphenols leads to greater inhibition. To minimize this interaction, it's recommended to consume tea or coffee between meals rather than with them.

Dietary Fiber

While dietary fiber is beneficial for gut health, high intake can have a minor, though not typically significant, impact on mineral absorption. The effect is largely attributed to the presence of associated anti-nutrients like phytates and the physical trapping of minerals within the fibrous matrix. Studies have shown that while high-fiber diets might slightly lower mineral levels, the overall effect is modest in individuals with adequate intake.

Other Factors Influencing Mineral Bioavailability

Mineral-Mineral and Nutrient Interactions

Some minerals compete for the same absorption pathways in the gut, and an excess of one can hinder the absorption of another. For example:

Zinc and Copper/Iron: High zinc intake can impair the absorption of copper and iron.
Calcium and Iron: High calcium intake, such as from dairy products, can inhibit non-heme iron absorption. Conversely, other nutrients can enhance mineral absorption. Vitamin C is a powerful enhancer of non-heme iron absorption, making it beneficial to pair iron-rich plant foods with sources of vitamin C. Vitamin D also boosts the absorption of calcium and magnesium.

Health Status and Life Stage

An individual's health and life stage play a significant role in mineral absorption. Conditions like Crohn's disease, celiac disease, or other malabsorption syndromes can directly impair the body's ability to absorb minerals. Additionally, as people age, gastric acid production naturally declines, which can reduce mineral absorption. Infants, pregnant and lactating women, and the elderly are particularly vulnerable to mineral deficiencies due to their unique physiological needs.

Food Processing and Preparation Methods

The way food is processed and prepared can either diminish or enhance mineral bioavailability.

Milling: While milling grains removes phytates found in the bran, it also removes other minerals present in the same layer.
Cooking and Leaching: Boiling vegetables can cause some minerals to leach out into the cooking water.
Soaking: Soaking legumes, grains, and nuts for several hours helps to activate the natural phytase enzymes, which break down phytic acid and improve mineral availability.
Sprouting (Germination): Sprouting seeds, grains, and legumes further activates phytase, leading to significant reduction in phytate content.
Fermentation: Fermentation, as seen in sourdough bread, promotes phytate breakdown due to the organic acids and microbial enzymes produced.

Comparison of Anti-Nutrients and Their Effects


Anti-Nutrient	Primary Source	Minerals Affected	Effect on Absorption	Mitigation Strategy
Phytic Acid	Whole grains, legumes, nuts, seeds	Iron, zinc, calcium, magnesium	Binds to form insoluble complexes, reducing absorption	Soaking, sprouting, fermentation
Oxalic Acid	Spinach, rhubarb, beet greens	Calcium, iron	Binds to form insoluble crystals, decreasing absorption	Boiling in water
Polyphenols/Tannins	Tea, coffee, cocoa, berries	Non-heme iron, zinc	Chelate minerals, especially non-heme iron	Consume beverages separately from iron-rich meals
Dietary Fiber	Whole grains, legumes, vegetables	Zinc, iron, calcium (indirectly)	Binds minerals or physically entraps them	No significant mitigation needed with balanced diet

Conclusion

While a variety of factors can decrease the bioavailability of minerals, dietary choices and preparation methods are within your control. The presence of anti-nutrients in many healthy plant foods is not a reason to avoid them. By utilizing simple culinary techniques like soaking, sprouting, and fermentation, and by being mindful of how you combine certain foods, you can significantly enhance your body's ability to absorb vital minerals. Pairing mineral-rich plant sources with enhancers like vitamin C, and maintaining a diverse diet, ensures you get the most nutritional value from your meals. Prioritizing proper food preparation is an effective strategy for preventing mineral deficiencies and supporting overall health. For further reading, an extensive review on anti-nutrients and their reduction strategies can be found here: Plant food anti-nutritional factors and their reduction strategies: an overview.

Frequently Asked Questions

Anti-nutrients are natural or synthetic compounds found in foods that interfere with the absorption of nutrients, including minerals. Examples include phytic acid, oxalic acid, and tannins.

Phytic acid binds with minerals like zinc, iron, and calcium in the digestive tract to form insoluble compounds. This binding process, called chelation, makes the minerals unavailable for the body to absorb.

Yes. You can improve mineral bioavailability by using preparation methods like soaking, sprouting, and fermentation to reduce anti-nutrient content. Pairing certain foods, like vitamin C with iron, also helps.

Yes, the polyphenols and tannins in coffee and tea can significantly inhibit the absorption of non-heme iron. It is best to drink these beverages between meals rather than with them if you are concerned about iron absorption.

High intake of dietary fiber can have a minor effect on mineral absorption, but this is usually not significant in a balanced diet. The effect is mainly attributed to the binding properties of associated anti-nutrients.

Cooking methods can have varied effects. While prolonged boiling can cause some minerals to leach into the water, heat treatments often help break down anti-nutrients like phytates and tannins, thus increasing mineral availability.

No. Many foods with anti-nutrients, such as whole grains and legumes, are highly nutritious. Avoiding them is not recommended. Instead, focus on using preparation techniques that reduce the anti-nutrient content and consume a balanced diet.