Do Tannins Cause Constipation? The Truth About Astringent Foods

November 25, 2025 •

3 min read

According to a 2015 study, the tannins in unripe bananas can reduce small intestinal secretions and inhibit peristalsis, potentially causing constipation. The question of whether tannins cause constipation is complex, with the effect depending on the type of tannin, the amount consumed, and an individual's digestive sensitivity.

Quick Summary

Tannins can contribute to constipation in some individuals due to their astringent properties, which bind to proteins and can slow digestion. Factors like dehydration and individual sensitivity play a significant role. Moderate intake of natural sources is generally well-tolerated, but high doses can cause adverse digestive effects.

Key Points

Astringent Effect: Tannins bind to proteins and other gut substances, creating a drying effect that can harden stool and contribute to constipation in some people.
Moderate Intake is Key: For most healthy individuals, moderate consumption of tannin-rich foods and beverages is unlikely to cause constipation. Problems generally arise with excessive intake.
Unripe Fruits are More Constipating: Unripe foods like bananas and persimmons have higher concentrations of constipating tannins than their ripe counterparts.
Hydration Matters: The diuretic effect of caffeine in beverages like black tea, combined with its tannins, can cause dehydration and worsen constipation if fluid intake is insufficient.
Individual Sensitivity is a Factor: People with sensitive digestive systems or certain health conditions may be more susceptible to the constipating effects of tannins than others.
Nutrient Absorption Interference: High tannin intake can hinder the absorption of minerals, especially iron, which is a particular concern for individuals with iron deficiency.
Preparation Can Reduce Tannins: Soaking and boiling can help reduce the tannin content in some foods, and using shorter steeping times for tea can also help.

Understanding Tannins and Their Effects on Digestion

Tannins are naturally occurring polyphenolic compounds found in many plants, giving them an astringent, bitter, or dry taste. In the digestive tract, tannins can bind to proteins and minerals, which is the basis for their potential link to constipation. The degree to which tannins affect digestion varies among individuals based on factors like gut sensitivity, diet, and hydration.

How Tannins May Lead to Constipation

Tannins can contribute to constipation through several mechanisms:

Astringent Action

The astringent property of tannins allows them to bind with proteins and other substances in the gut, which can lead to a drying effect on the intestinal lining and stool. This can make stools harder and more challenging to pass, potentially causing or worsening constipation, particularly with foods high in astringent tannins like unripe bananas and persimmons.

Inhibition of Digestive Enzymes

Tannins may also interfere with the function of digestive enzymes by forming complexes with them. While moderate amounts typically don't cause significant problems in healthy adults, excessive consumption could slow down the digestive process, leading to a sluggish gut and potential constipation.

Interaction with Hydration

For beverages containing both tannins and caffeine, such as black tea and coffee, dehydration can be an additional factor. Caffeine is a diuretic, increasing fluid loss. Consuming large quantities of these drinks without adequate water intake can result in drier, harder stools that are difficult to eliminate, despite caffeine's potential to stimulate the bowels.

Factors Influencing the Effect of Tannins

The impact of tannins on digestion is influenced by several variables:

Source: Tannins from different plant sources can have varying effects.
Amount and Frequency: The risk of issues increases with high or frequent consumption.
Individual Sensitivity: People with sensitive digestive systems may be more affected.
Preparation: Methods like soaking, boiling, or shorter steeping times can reduce tannin content.

Strategies to Mitigate Tannin-Related Constipation

To enjoy tannin-rich foods while minimizing the risk of constipation:

Ensure adequate hydration, especially when consuming caffeinated drinks.
Consume tannin-rich beverages between meals to avoid interfering with mineral absorption.
Moderate your intake of high-tannin foods and drinks, particularly if you are sensitive.
Adding milk (for its proteins) or lemon (for vitamin C) to tea can help bind some tannins.
Choose ripe fruits like bananas over unripe ones, as tannin levels decrease during ripening.

High-Tannin vs. High-Fiber Foods


Feature	Tannin-Rich Foods (e.g., Unripe Bananas, Black Tea)	Fiber-Rich Foods (e.g., Ripe Bananas, Oats)
Effect on Stool	Can lead to hard, dry stools by binding to proteins and slowing intestinal movement.	Adds bulk and softness to stool, promoting regular bowel movements.
Digestive Impact	May slow down intestinal motility and potentially cause irritation in sensitive individuals.	Increases intestinal contractions (peristalsis), which helps move food through the digestive tract.
Hydration Factor	Some sources (like caffeinated teas) are diuretics, increasing the risk of dehydration-related constipation.	Fiber absorbs water, which is crucial for forming soft, manageable stool. Adequate fluid intake is essential.
Nutrient Absorption	Can bind to minerals like iron, potentially hindering their absorption.	Does not interfere with mineral absorption in the same manner. Supports overall digestive health.
Best for Constipation	Should be limited or avoided if constipation is a concern, especially in sensitive people.	Highly recommended for preventing and relieving constipation.

Conclusion

While tannins can contribute to constipation in certain individuals, they are not universally constipating. The risk is heightened by excessive consumption of high-tannin foods, particularly when combined with insufficient hydration or pre-existing digestive sensitivity. The key mechanism is the astringent property of tannins, which binds to proteins and can reduce intestinal motility. For most people, moderate consumption of tannin-rich items and maintaining good hydration are sufficient to prevent digestive issues. Those with chronic or sensitive digestive systems should monitor their intake and consider milder or properly prepared alternatives. For more information on tannins, consult this Los Angeles Times article.

Frequently Asked Questions

Yes, black tea can cause constipation in some individuals. While its caffeine content can stimulate bowel movements, its tannins have an astringent effect that can slow digestion. Dehydration from the diuretic effect of caffeine can also contribute to harder stools.

Foods particularly noted for their constipating tannins include unripe bananas and astringent persimmons. Other sources include black tea, coffee, red wine, chocolate, and some legumes, though their effects vary.

No, not all foods with tannins cause constipation. The effect depends on the amount of tannins, the individual's sensitivity, and other factors like hydration. Many tannin-rich foods have beneficial properties, but overconsumption can be problematic for some.

To minimize the constipating effect of tannins in tea, you can steep it for a shorter duration or at a lower temperature. Adding a splash of milk can also help, as the proteins in milk bind with some of the tannins.

Tannins can slow digestion and harden stool by binding to proteins, whereas fiber (especially insoluble fiber) adds bulk and softens stool, promoting regular bowel movements. Adequate hydration is key for both to function properly.

Unripe bananas contain a high concentration of tannins and starch, which can cause or worsen constipation. As bananas ripen, the tannins decrease significantly, making them less constipating and sometimes even helpful for regularity.

Someone with chronic constipation or a sensitive digestive system should be mindful of their tannin intake, but may not need to avoid them completely. Focusing on moderation, increasing hydration, and observing personal triggers is a better approach.