Is Natto Good for Fertility? An In-Depth Nutritional Guide

November 14, 2025 •

6 min read

Recent studies suggest a link between gut health and reproductive outcomes, making the probiotic-rich profile of natto an interesting topic for those exploring diet's role in conception. The question of whether natto is good for fertility involves understanding its unique nutritional composition and its specific effects on both male and female reproductive systems.

Quick Summary

This nutritional guide examines the evidence behind natto's potential to support fertility, detailing its key nutrients like vitamin K2, probiotics, and isoflavones. It explains how these components may benefit reproductive health while addressing the important distinction between fermented and unfermented soy products. The article also provides dietary considerations and answers frequently asked questions about including natto in a pro-fertility diet.

Key Points

Fermented vs. Unfermented Soy: Natto is a fermented soy product, which enhances its nutrient profile and is generally considered more beneficial for fertility than large quantities of unfermented soy.
Rich in Vitamin K2: Natto is a potent source of vitamin K2 (MK-7), which supports cardiovascular health, reduces inflammation, and may aid bone health, all factors that contribute to overall reproductive health.
Probiotic Power: The Bacillus subtilis bacteria in natto provide powerful probiotics that promote a healthy gut microbiome, which in turn influences immune function, hormone metabolism, and fertility outcomes.
Contains Key Nutrients: Natto is rich in folic acid and iron, both essential nutrients for fertility and healthy pregnancy development.
Supports Both Male and Female Fertility: Research suggests potential benefits for both men (improved sperm health in animal models) and women (potential to aid in endometriosis management and IVF outcomes).
Considerations for Anticoagulants: Individuals on blood-thinning medication should consult a doctor before consuming natto due to its high vitamin K content, which can affect clotting.

The Fermented Advantage: Why Natto's Processing Matters

Natto, a traditional Japanese food made from fermented soybeans, stands apart from other soy products like tofu or soy milk due to its unique preparation with the bacterium Bacillus subtilis. This fermentation process is key to unlocking many of its potential health benefits, transforming the nutritional profile of the soybeans in several crucial ways. First, fermentation enhances the bioavailability of nutrients, making them easier for the body to absorb. Second, it creates beneficial probiotics that contribute to a healthy gut microbiome, an aspect of health increasingly linked to reproductive function. Unlike unfermented soy, which some studies have suggested might interfere with reproductive hormones in high doses, fermented soy products like natto are generally considered safe and potentially beneficial when consumed in moderation.

Natto's Powerhouse Nutrients for Reproductive Health

Natto contains a variety of vitamins and minerals essential for optimal reproductive health in both men and women. These include:

Vitamin K2 (MK-7): Natto is one of the richest dietary sources of this vitamin, which plays a role beyond blood clotting. MK-7 may help improve cardiovascular health and reduce inflammation, both of which are important for overall well-being and, indirectly, fertility. Some research suggests that vitamin K2 may also be important for bone health and proper nutrient utilization, including calcium.
Probiotics: The fermentation process with Bacillus subtilis endows natto with a potent dose of probiotics. A healthy gut microbiome is crucial for modulating inflammation, immune function, and hormone metabolism, which all have an impact on fertility.
Folic Acid (Folate): An essential B vitamin, folate is critical for DNA synthesis and repair, and is vital for fetal development during early pregnancy. Including folate-rich foods like natto in a pre-conception diet can help ensure adequate levels.
Iron: Adequate iron is necessary for preventing anemia, which can be detrimental to reproductive health and increase the risk of premature birth. Natto provides a good source of plant-based iron.
Isoflavones: The isoflavones in fermented soy are metabolized differently than in unfermented forms, which may enhance their hormone-balancing potential. For women, some research suggests a potential link between moderate soy intake and higher live birth rates during IVF treatment. For men, while some studies found an association between high isoflavone intake and lower sperm concentration, this is typically linked to very high-dose supplements rather than moderate dietary consumption of fermented soy.

Potential Benefits of Natto for Female and Male Fertility

For Female Fertility

Endometriosis Support: The enzyme nattokinase, found in natto, has been explored for its fibrinolytic properties, which may help break down fibrin and reduce the adhesions associated with conditions like endometriosis. While more research is needed, this offers a potential supportive role.
Improved Egg Quality: A healthy gut microbiome and reduced systemic inflammation, both supported by natto's components, are linked to improved egg quality, especially in women with inflammatory conditions.
Hormonal Balance: Fermented soy's isoflavones may help regulate hormones, supporting a more favorable uterine environment for implantation.

For Male Fertility

Increased Testosterone and Sperm Quality: A 2016 study on hypercholesterolemic male mice found that black soybean natto extract increased testosterone levels and improved sperm density and motility. This suggests a potential benefit for men with certain metabolic issues, though human research is needed.
Protection Against Oxidative Stress: Natto contains antioxidants that can protect sperm cells from free radical damage, a known factor in male infertility.
Enhanced Blood Flow: Nattokinase's ability to support cardiovascular health and thin the blood may improve overall circulation, potentially benefiting reproductive organ function.

Comparison: Natto vs. Unfermented Soy for Fertility


Feature	Natto (Fermented Soy)	Unfermented Soy (Tofu, Soy Milk)
Processing	Soybeans fermented with Bacillus subtilis.	Soybeans processed without fermentation.
Nutrient Absorption	Higher bioavailability of key minerals due to reduced phytate content.	Higher phytate content may bind minerals, potentially inhibiting absorption.
Hormonal Impact	Isoflavones are more easily absorbed and potentially more effective for hormone modulation.	High intake may interfere with thyroid hormones and affect ovulation in some sensitive individuals.
Probiotics	Rich source of beneficial Bacillus subtilis probiotics.	Does not contain significant probiotic content.
Nattokinase	Contains the enzyme nattokinase, which supports cardiovascular health.	Does not contain nattokinase.
Best For Fertility?	Preferred choice; beneficial components and lower risk profile.	Consume in moderation; high intake is linked to hormonal concerns in some studies.

Conclusion: Making an Informed Dietary Choice

Ultimately, the question of "Is natto good for fertility?" is best answered by highlighting its role as part of a balanced, whole-food diet. The fermentation process makes it a unique and valuable addition to a reproductive health regimen, offering a concentrated source of probiotics, vitamin K2, and other key nutrients that support overall well-being. Its potential benefits for improving egg quality, supporting hormonal balance, and enhancing male reproductive parameters suggest a promising role. However, as with any dietary component, moderation is key. It is always best to consult a healthcare provider or a registered dietitian, especially when managing specific health conditions or taking medications, to ensure natto is a suitable and beneficial addition to your personal journey toward conception. As research continues to unravel the intricate links between diet, gut health, and reproduction, incorporating nutrient-dense, fermented foods like natto could be a proactive step toward supporting fertility.

Optional Link: For further information on the specific properties of nattokinase, an enzyme unique to natto, you can visit RxList's nattokinase page.

How to Incorporate Natto into Your Diet

Start Small: Begin by adding a small amount of natto to a bowl of rice or a salad. The flavor is an acquired taste for many.
Mix with Flavors: Incorporate strong flavors to help mask the distinct taste and aroma. Traditional pairings include soy sauce, mustard, and green onions.
Add to Soups or Scrambled Eggs: Stir natto into miso soup or scrambled eggs just before serving to add a nutritious, probiotic-rich boost.
Use Natto Powder: For those who cannot tolerate the texture or taste, natto powder offers the benefits of nattokinase and other nutrients without the stickiness.

How to Manage Potential Natto Side Effects

Gradual Introduction: Introduce natto into your diet slowly to allow your digestive system to adjust to the new probiotics.
Avoid with Anticoagulants: If you are taking anticoagulant medication, consult your doctor before consuming natto due to its high vitamin K content and nattokinase, which can affect blood clotting.
Check for Soy Allergy: Those with a soy allergy should avoid natto entirely.

Natto and Male Fertility

Boost Testosterone: A 2016 study on male mice showed that black soybean natto extract increased testosterone levels in hypercholesterolemic subjects.
Improve Sperm Health: Fermented soy's antioxidants may help protect sperm from damage caused by free radicals.

Natto and Female Fertility

Enhanced IVF Outcomes: Moderate soy intake, especially fermented, has been linked to higher clinical pregnancy and live birth rates in women undergoing IVF.
Uterine Receptivity: Soy isoflavones in natto might support a healthy uterine environment conducive to embryo implantation.
Fights Endometriosis: Nattokinase in natto has potential to help break down adhesions associated with endometriosis, though more research is needed.

A Note on Unfermented Soy

Potential Hormonal Interference: Unlike natto, high intake of unfermented soy products like tofu and soy milk may interfere with hormone production and ovulation in certain individuals.
Moderate Consumption is Key: For unfermented soy, consuming in moderation as part of a balanced diet is recommended for those trying to conceive.

Consult Your Doctor

Personalized Advice: While natto offers potential fertility benefits, it is crucial to consult a healthcare provider or fertility specialist for personalized advice, especially if you have existing health conditions or are on medication.

Conclusion

By understanding the unique properties of fermented soy and its concentrated nutrient profile, you can make an informed decision about whether to include natto in your diet as part of a holistic approach to enhancing fertility.

Frequently Asked Questions

Moderate consumption of fermented soy like natto is unlikely to interfere with hormone levels. The isoflavones in fermented soy are metabolized differently than in unfermented soy, and studies suggesting hormonal disruption typically involve high doses of isolated soy compounds, not whole food intake.

The enzyme nattokinase, found in natto, has been studied for its potential to help break down fibrin, which is involved in forming the adhesions associated with endometriosis. While more human research is needed, it offers a potential supportive benefit for managing the condition.

Yes, some animal studies suggest that natto extract can increase testosterone levels and improve sperm density and motility, particularly in cases of high cholesterol. Natto's antioxidants also protect sperm from oxidative stress.

Natto is fermented, which increases the bioavailability of its nutrients and provides beneficial probiotics. Unfermented soy products may have a different hormonal impact in high quantities due to their isoflavones, whereas fermented products are generally seen as more beneficial and safer for fertility.

Natto is rich in nutrients like folic acid and iron, which are excellent for pregnancy. However, due to its vitamin K content and blood-thinning properties, women should consult their healthcare provider before consuming it, especially if they are on any medication.

If you dislike the taste or texture of natto, you can find natto powder or nattokinase supplements. These provide many of the beneficial enzymes and nutrients, though consulting a doctor before taking supplements is recommended.

Some individuals may experience digestive discomfort when first introducing natto due to its high fiber and probiotic content. The most important consideration is its effect on blood clotting, so individuals on anticoagulants should avoid it unless advised by a physician.