Understanding Nutrition: What are the side effects of antinutrients?

November 1, 2025 •

4 min read

Naturally occurring compounds in many plant-based foods can interfere with the body's ability to absorb and use essential nutrients. In a world focused on plant-based diets, understanding these substances is crucial. So, what are the side effects of antinutrients, and when should you be concerned?

Quick Summary

Antinutrients, including lectins, phytates, and oxalates, can inhibit mineral absorption and cause digestive issues. Processing methods can significantly reduce their impact on nutrient bioavailability.

Key Points

Nutrient Absorption Interference: The primary side effect of antinutrients is their ability to bind with minerals like iron, zinc, and calcium, reducing their absorption.
Digestive Issues: Some antinutrients, particularly lectins, can cause acute digestive distress, including nausea, bloating, and abdominal pain in sensitive individuals.
Kidney Stone Risk: A high intake of oxalates, found in many healthy foods, can increase the risk of calcium oxalate kidney stones, especially for susceptible people.
Thyroid Disruption: Goitrogens, present in cruciferous vegetables and soy, can interfere with iodine utilization by the thyroid gland, potentially leading to thyroid issues with high intake and iodine deficiency.
Cooking and Preparation are Key: Methods such as soaking, cooking, sprouting, and fermentation are highly effective at reducing the antinutrient content in foods.
Balanced Diet is Safest: For most people, a varied and balanced diet minimizes the impact of antinutrients, with the health benefits of plant foods outweighing the potential risks.

What are antinutrients?

Antinutrients are natural or synthetic compounds found in various foods that interfere with the absorption of other nutrients. Primarily found in plant-based foods such as grains, legumes, nuts, and seeds, they act as part of the plant's defense mechanism. While typically not a concern for most individuals consuming a balanced diet, excessive intake or consumption by those with specific health conditions can lead to adverse effects. The concept follows the principle that 'the dose makes the poison,' meaning smaller amounts are generally harmless, and some antinutrients even offer health benefits.

Side effects of specific antinutrients

Different types of antinutrients cause a range of specific side effects due to their unique interactions within the human body. Understanding these can help you better manage your diet and cooking methods.

Phytates (Phytic Acid)

Phytates are found in whole grains, seeds, legumes, and nuts. They are a primary concern for mineral absorption:

Mineral binding: Phytic acid strongly binds to essential minerals like iron, zinc, magnesium, and calcium in the digestive tract, forming insoluble compounds. This chelation process prevents the body from absorbing these minerals.
Nutritional deficiencies: Over time, high-phytate diets, particularly in populations heavily dependent on unprocessed grains, can lead to chronic mineral deficiencies. In severe cases, this could contribute to conditions like osteoporosis or rickets, though this is rare in balanced diets.
Enzyme inhibition: Phytates can also inhibit digestive enzymes, such as pepsin and amylase, which are necessary for digesting proteins and starches, respectively.

Lectins

Lectins are a family of proteins abundant in legumes and grains. While many lectins are harmless, some can cause issues if not properly prepared:

Digestive discomfort: Certain lectins, like phytohemagglutinin in red kidney beans, can bind to the cells lining the digestive tract, causing acute symptoms like nausea, vomiting, and diarrhea.
Altered gut function: For sensitive individuals, lectins may contribute to altered gut function and inflammation. Some theories link them to intestinal permeability, or 'leaky gut,' but this area requires further research.
Potential immune response: In some individuals, lectins have been anecdotally linked to autoimmune symptoms, but this is not yet a scientific consensus.

Oxalates (Oxalic Acid)

Oxalates are found in green leafy vegetables, nuts, legumes, and certain root vegetables like spinach and rhubarb.

Kidney stone formation: The most significant risk from high oxalate intake is the increased chance of forming calcium oxalate kidney stones. Oxalates bind with calcium, and in high concentrations, can form painful crystals in the urinary tract.
Nutrient malabsorption: Similar to phytates, excessive oxalate consumption can interfere with the absorption of minerals like calcium and magnesium.
Other symptoms: Some individuals report a phenomenon called 'oxalate dumping' when changing their diet, with symptoms including joint pain, fatigue, and rashes, though this is not a formally recognized medical condition.

Tannins

Found in tea, coffee, wine, and legumes, tannins are known for their astringent properties.

Reduced iron absorption: Tannins are well-known inhibitors of non-heme iron absorption. Drinking tea with meals, for example, can significantly reduce the amount of iron the body absorbs from plant-based foods.
Digestive irritation: In high concentrations, tannins can cause digestive irritation, nausea, and vomiting.

Goitrogens

Goitrogens are compounds found in cruciferous vegetables like broccoli, kale, and cabbage, as well as in soy and millet.

Thyroid function interference: Goitrogens interfere with iodine uptake by the thyroid gland, which can disrupt thyroid hormone production.
Hypothyroidism and goiter: While cooking significantly reduces goitrogenic activity, very high, raw consumption combined with an iodine deficiency can lead to hypothyroidism or goiter (enlargement of the thyroid gland).

Mitigating the effects of antinutrients

Fortunately, several traditional food preparation methods can effectively reduce the levels of most antinutrients.

Soaking: Soaking grains, legumes, and nuts in water overnight before cooking can help reduce phytates and lectins. Discarding the soaking water is key.
Cooking: Applying heat through boiling or steaming is highly effective at reducing heat-labile antinutrients like lectins and some oxalates. Boiling can be especially effective.
Fermentation: This process involves microorganisms breaking down plant compounds, which can significantly reduce phytates and lectins. Examples include sourdough bread and fermented soy products.
Sprouting (Germination): Sprouting activates enzymes within the plant that can degrade antinutrients, enhancing digestibility and nutrient bioavailability.

Comparison of Major Antinutrients and Their Effects


Antinutrient	Found In	Primary Side Effects	Method to Reduce
Phytates	Grains, legumes, seeds, nuts	Blocks absorption of iron, zinc, calcium, magnesium; inhibits digestive enzymes.	Soaking, sprouting, fermentation, cooking.
Lectins	Legumes, whole grains	Digestive distress (nausea, vomiting), altered gut function.	Soaking, high-heat cooking.
Oxalates	Leafy greens, nuts, legumes	Binds calcium, increasing risk of kidney stones; hinders mineral absorption.	Cooking (especially boiling), steaming.
Tannins	Tea, coffee, wine, legumes	Reduces non-heme iron absorption; potential digestive upset in high doses.	Brewing tea between meals instead of with them.
Goitrogens	Cruciferous vegetables, soy, millet	Disrupts iodine uptake and thyroid hormone function.	Cooking.

Conclusion

While the prospect of antinutrient side effects may seem concerning, a balanced and varied diet, combined with proper food preparation, makes these risks minimal for most healthy individuals. For those with pre-existing conditions like hypothyroidism, kidney issues, or specific sensitivities, paying closer attention to antinutrient intake and preparation is more important. The overall benefits of consuming plant-based foods, such as fiber, vitamins, and other beneficial compounds, far outweigh the potential negatives of antinutrients when consumed as part of a diverse and healthy diet. Always consult a healthcare provider or registered dietitian for personalized advice, especially if you have chronic health concerns related to diet.

An excellent overview of antinutrients and their effects can be found in this article on ScienceDirect: Antinutrients in Plant-based Foods: A Review.

Frequently Asked Questions

The most common antinutrients include phytates (phytic acid), lectins, oxalates (oxalic acid), tannins, and goitrogens. They are found in grains, legumes, nuts, seeds, and certain vegetables.

No, the effect of antinutrients varies significantly among individuals. Factors like overall diet, digestive health, and specific pre-existing conditions (e.g., hypothyroidism, kidney issues) determine how an individual responds.

Cooking and preparation methods like soaking, boiling, and fermentation can significantly reduce antinutrient levels. While not all are completely eliminated, these methods make the food much safer and more nutritious for consumption.

No, you should not avoid these foods entirely. Many foods containing antinutrients are highly nutritious and beneficial. Instead, focus on proper preparation techniques and a balanced diet to minimize any negative effects.

Phytates bind to minerals like iron, zinc, and calcium in the digestive tract, forming insoluble complexes that the body cannot absorb. This can lead to deficiencies over time with chronic high intake.

Yes, some antinutrients have been shown to have potential health benefits at lower concentrations, including antioxidant effects and anti-cancer properties. The effect is dose-dependent.

Yes, it is generally safe to eat raw cruciferous vegetables as part of a balanced diet. However, individuals with thyroid issues who also have an iodine deficiency might consider cooking them to reduce goitrogenic activity.

'Oxalate dumping' is a term used by some to describe symptoms like fatigue, rashes, and pain experienced when a person significantly lowers their oxalate intake. It is not a recognized medical diagnosis.