What Does Tannin Do to Humans: Benefits and Downsides Explored

December 17, 2025 •

4 min read

Tannins are a category of polyphenols found in various plants, with an estimated daily human intake of up to 1 gram. What does tannin do to humans? These compounds are well-known for contributing to the astringent, bitter taste in foods like tea, coffee, and wine, but their influence on the human body extends far beyond taste, encompassing both potential health benefits and some downsides.

Quick Summary

Tannins are plant-based polyphenols with diverse effects on the human body, providing antioxidant, anti-inflammatory, and antimicrobial benefits. Excessive intake, however, can interfere with iron absorption and cause digestive upset. The overall impact depends heavily on dosage, dietary context, and an individual's unique biology.

Key Points

Antioxidant Benefits: Tannins are powerful antioxidants that protect against cellular damage from free radicals and reduce the risk of chronic diseases.
Anti-inflammatory Effects: They can help reduce inflammation throughout the body, including promoting a healthier gut barrier.
Impeded Iron Absorption: High tannin intake, especially with meals, can inhibit the absorption of non-heme iron, an important consideration for individuals with low iron levels.
Digestive Upset: Consuming large quantities of tannins on an empty stomach can cause gastrointestinal issues like nausea in some sensitive individuals.
Positive Gut Microbiome Interaction: The fermentation of tannins by gut bacteria produces beneficial metabolites that offer systemic health effects and support gut health.
Varies by Individual and Source: The effect of tannins depends on their type, concentration, an individual's gut microbiome, and overall dietary habits.
Food Preparation Can Alter Levels: Soaking and boiling legumes can reduce their tannin content, mitigating some anti-nutritional effects.

The Dual Nature of Tannins: Benefits and Risks

Tannins are complex, water-soluble phenolic compounds found in a wide variety of plant-based foods, including teas, wines, nuts, berries, and legumes. While traditionally viewed as 'antinutrients' due to their ability to bind with proteins, modern research reveals a more nuanced picture of how they affect human health, highlighting both protective properties and potential drawbacks depending on consumption habits.

Health Benefits Associated with Tannin Intake

Moderate consumption of tannins is linked to several positive health outcomes, primarily attributed to their powerful antioxidant and anti-inflammatory properties.

Antioxidant Effects: Tannins act as potent antioxidants, neutralizing harmful free radicals that can damage cells and contribute to chronic diseases. Their rich polyphenolic structure allows them to protect against oxidative stress, which is a key factor in aging and various pathologies.
Cardioprotective Properties: Studies indicate that tannins can contribute to cardiovascular health. They have been shown to help lower blood pressure and reduce levels of 'bad' LDL cholesterol, thereby decreasing the risk of atherosclerosis.
Anti-Inflammatory Action: By inhibiting inflammatory pathways and mediating cytokine expression, tannins can help reduce systemic inflammation. This is particularly relevant for maintaining gut barrier integrity and overall gastrointestinal health.
Antimicrobial and Antiviral Activity: The ability of tannins to bind to proteins can also inhibit the growth of various microorganisms, including bacteria, fungi, and viruses. This antimicrobial action can offer a natural defense against infections.

Potential Downsides and Factors Affecting Digestion

Despite their benefits, high tannin intake can lead to certain negative effects, especially for sensitive individuals or when consumed in excess.

Iron Absorption Inhibition: One of the most significant downsides is the tannins' ability to chelate, or bind to, non-heme iron (the form of iron found in plant-based foods) in the digestive tract. This can significantly reduce iron absorption, which is a concern for people with or at risk of iron deficiency anemia. For this reason, those with low iron are often advised to avoid drinking tea with meals.
Digestive Discomfort: The same protein-binding property that causes the dry, puckering sensation in the mouth can also cause gastrointestinal irritation. High tannin consumption, particularly on an empty stomach, can lead to nausea, vomiting, or stomach upset in some individuals.
Protein Digestibility: As 'antinutrients', tannins have long been known to interfere with the absorption and utilization of proteins and certain minerals. However, the impact varies, and studies suggest the effect is not as severe with regular, moderate intake as was once thought, particularly in diets that are otherwise nutritionally sound.

Tannin Sources and Dietary Modifications

Not all tannins are created equal. Their concentration and type (e.g., condensed vs. hydrolyzable) vary significantly between foods and can be influenced by preparation methods. You can manage your tannin intake by understanding common sources and how processing affects them.

Comparison of Tannin-Rich Foods and Their Effects


Food/Beverage	Common Tannin Type	Effect on Astringency	Iron Absorption Impact	Notes
Black Tea	Hydrolyzable	High	Significant reduction when consumed with meals	Steeping for less time can reduce tannin levels.
Red Wine	Condensed	High, creates structure	Minimal impact on overall iron status	Tannins soften with aging, becoming smoother.
Dark Chocolate	Condensed (Procyanidins)	Moderate	Minimal, often consumed in lower quantities	Antioxidant benefits are often highlighted.
Berries (Cranberries, Pomegranates)	Condensed (Proanthocyanidins) and Ellagitannins	Moderate to High	Low impact in whole food form	High in beneficial antioxidants.
Legumes (Beans)	Condensed	Varies (depends on color and type)	Soaking and boiling can reduce tannin content.	Offers protein and other nutrients alongside tannins.

How to Minimize Negative Effects of Tannins

Consume between meals: If you are concerned about iron absorption, drinking tea or coffee between meals rather than with them can mitigate the tannins' effect on nutrient uptake.
Add milk: The proteins in milk can bind to tannins, which reduces their astringency and lessens their potential for gastric irritation.
Use proper brewing techniques: For tea and coffee, using a lower water temperature or steeping for a shorter duration can reduce the extraction of tannins.
Cook high-tannin foods: Soaking and boiling legumes can significantly decrease their tannin content.

The Gut Microbiota and Tannins

The story of tannins' effect on humans is incomplete without considering the gut microbiome. While tannins have low bioavailability and are poorly absorbed in the small intestine, they are fermented by bacteria in the colon. This fermentation process produces beneficial metabolites, such as urolithins, which are then absorbed and can exert systemic effects. The gut's ability to break down tannins means that what starts as an 'antinutrient' can be converted into an anti-inflammatory and antioxidant compound that supports intestinal health and may even influence longevity. The specific composition of an individual's gut microbiome can influence how efficiently these compounds are metabolized and therefore how a person experiences tannins.

Conclusion

In conclusion, the question of what tannin does to humans has a complex answer. These plant compounds contribute flavor and color to many foods and offer a range of significant health benefits, including antioxidant, anti-inflammatory, and cardioprotective effects. However, their ability to bind proteins can lead to some negative outcomes, most notably the inhibition of iron absorption and potential digestive upset in sensitive individuals. For most people, moderate consumption of tannin-rich foods and beverages is not a concern, and the benefits likely outweigh the risks. By being mindful of consumption patterns—such as drinking tea between meals rather than with them—individuals can harness the advantages of tannins while minimizing their drawbacks. For those with pre-existing conditions like iron deficiency anemia, dietary adjustments may be prudent. As with all dietary components, the overall context of one's diet and individual biological factors dictate the final health impact.
Note: This article is for informational purposes only and is not medical advice. Consult a healthcare professional before making any significant dietary changes.

Frequently Asked Questions

Tannins are found in a wide variety of plant-based foods and beverages. The most common sources include tea (especially black tea), coffee, red wine, dark chocolate, berries, pomegranates, nuts, and legumes.

Yes, high levels of tannins, particularly when consumed on an empty stomach, can cause stomach irritation, nausea, and digestive upset in some people. Consuming them with food or milk can help mitigate this effect.

The connection between tannins and migraines is often claimed anecdotally, particularly regarding red wine, but scientific evidence to support this link is currently limited or inconclusive. Other compounds in wine are also considered potential triggers.

For most people with healthy iron levels, drinking tea with a meal is not a significant concern. However, for those with or at risk of iron deficiency, it is best to drink tea between meals rather than with them to maximize iron absorption.

Tannins are neither exclusively good nor bad. They offer numerous health benefits, such as antioxidant and anti-inflammatory properties, but can also interfere with nutrient absorption. The overall effect depends on the amount consumed, the source, and individual biology.

Several methods can reduce tannin content. For tea, a shorter brewing time or lower water temperature can help. For legumes and nuts, soaking and boiling can significantly decrease their tannin levels.

Tannins are a type of polyphenolic compound, and many of them, particularly those found in tea, wine, and fruit, function as powerful antioxidants in the body. So while all tannins are not antioxidants, most possess strong antioxidant activity.