Understanding the Health Profile of Natto
Natto, a traditional Japanese food made from fermented soybeans, is packed with beneficial nutrients, including fiber, protein, and powerful probiotics. However, it is also a rich source of specific compounds that can present risks for certain individuals. The fermentation process introduces the enzyme nattokinase and produces significant amounts of vitamin K2, specifically menaquinone-7 (MK-7), both of which are central to understanding the potential downsides of consuming this food.
The Critical Interaction with Blood-Thinning Medication
The most significant and well-documented risk of eating natto is its potential interaction with blood-thinning (anticoagulant) medications, such as warfarin (Coumadin).
- Vitamin K2 and its Role: Natto is one of the richest food sources of vitamin K2. Vitamin K is essential for the production of several clotting factors in the liver. A sudden increase in vitamin K intake can counteract the effect of warfarin, which is designed to inhibit vitamin K's function. This interference can make the medication less effective, increasing the risk of dangerous blood clots.
- Nattokinase's Effect: While vitamin K2 promotes clotting, natto also contains nattokinase, an enzyme that can break down existing blood clots. For individuals already on anticoagulants, this dual action can be unpredictable and potentially dangerous without a doctor's supervision. The combination could lead to dangerously thin blood and excessive bleeding. Therefore, anyone taking warfarin or similar medication must consult a doctor before adding natto to their diet.
Allergic Reactions and Immunocompromised Concerns
Though rare, allergic reactions to natto can occur, similar to other food allergies. Individuals with known soy allergies should avoid natto entirely, as it is made from soybeans. Some research has also documented rare cases of delayed-onset anaphylaxis specifically linked to natto, even in people without a prior soy allergy.
For those with severely compromised immune systems, such as patients undergoing hemodialysis or receiving potent immunosuppressive therapy, the live bacteria (Bacillus subtilis var. natto) in natto can pose a risk. In extremely rare instances, this can lead to bacteremia (a bacterial infection in the bloodstream), as documented in one case study of a patient with multiple health conditions. This risk is not present for healthy individuals with normal immune function.
Digestive Issues and High Purine Content
For new consumers, or those eating excessively large portions, natto can cause digestive upset. The high fiber and probiotic content can lead to gas, bloating, or diarrhea as the gut adjusts. It is best to start with small portions to allow the body to acclimatize to this fermented food. Additionally, due to its high purine content, excessive natto consumption could potentially increase the risk of gout in susceptible individuals.
Considerations for Thyroid Health
Like other soy products, natto is considered a goitrogen, which are substances that can interfere with the function of the thyroid gland. While the fermentation process can mitigate some of these effects, people with hypothyroidism or an already poorly functioning thyroid may want to moderate their intake and consult with a healthcare provider. This is unlikely to be a concern for individuals with healthy thyroid function.
Comparison of Natto and Nattokinase Risks
To provide clarity, it's helpful to distinguish between the risks associated with eating the food natto and those related to taking concentrated nattokinase supplements, which are more potent and unregulated.
| Feature | Natto (Food) | Nattokinase (Supplement) |
|---|---|---|
| Regulation | Regulated as a food product. | Less strictly regulated by the FDA; manufacturers self-regulate for safety and labeling. |
| Composition | Contains nattokinase, vitamin K2, protein, fiber, and other nutrients. | Concentrated nattokinase enzyme, often with vitamin K2 removed. |
| Risk with Anticoagulants | Interference is possible due to vitamin K2 content; medical consultation is vital. | May have a stronger interaction with blood thinners due to high enzyme concentration; medical supervision is crucial. |
| Bleeding Risk | Lower risk of excessive bleeding compared to supplements, but still a concern with blood thinners. | Increased risk of excessive bleeding and bruising, especially with other blood-thinning drugs. |
| Allergy Potential | Possible allergic reaction due to soybeans or the fermented product itself. | Potential for allergic reaction to the concentrated enzyme. |
Conclusion
While natto is a highly nutritious and generally safe food for most people, specific health considerations warrant caution. The primary risk revolves around its high vitamin K2 content, which can compromise the effectiveness of blood-thinning medications like warfarin. Individuals with a soy allergy should avoid natto entirely, and those with weakened immune systems should discuss its consumption with a doctor due to the presence of live bacteria. Other potential side effects, such as temporary digestive issues or concerns for thyroid function in susceptible individuals, can usually be managed by starting with small portions and monitoring intake. As with any dietary change, especially if you have an underlying health condition, consulting a healthcare professional is the safest approach to incorporate natto into your diet.
Potential Complications of Natto Consumption
- Drug Interactions: Natto contains high levels of vitamin K2, which can counteract the effects of blood-thinning medications like warfarin.
- Allergic Reactions: Individuals with a soy allergy should avoid natto, and even those without a soy allergy may have a rare reaction to the fermented product.
- Digestive Upset: The high fiber and probiotic content can cause gas, bloating, or diarrhea, particularly for those new to fermented foods.
- Bleeding Risks: Due to the combined effects of vitamin K2 and nattokinase, natto should be avoided before surgery to prevent excessive bleeding.
- Immunocompromised Risk: In extremely rare cases, individuals with compromised immune systems could develop an infection from the live bacteria in natto.
- Thyroid Function: Natto is a goitrogen, and people with existing thyroid issues should consume it with caution.
- Blood Pressure Fluctuation: The blood-pressure-lowering effect of nattokinase can be a concern for those with naturally low blood pressure or taking blood pressure medication.
Final Recommendations
For most healthy adults, eating natto in moderation is safe and provides numerous health benefits. The risks are typically low but become more significant for individuals with specific medical conditions or those taking certain medications. Always prioritize speaking with a healthcare provider to ensure natto is a safe addition to your diet, especially if you have pre-existing health issues or are on prescription medications.
Further Reading
For more information on the health benefits and risks of natto, consult reputable health sources and scientific research. Always cross-reference information and consider discussing it with a registered dietitian or physician.
Nattokinase: Benefits and side effects according to studies
How to Safely Consume Natto
- Consult a doctor: If you take blood thinners, have a thyroid condition, or have a compromised immune system, it is essential to get medical advice before consuming natto.
- Start small: For new consumers, begin with a small portion to allow your digestive system to adapt to the high fiber and probiotic content.
- Consider portion size: Enjoy natto as a healthy side dish rather than a main entree to avoid excessive intake of purines or isoflavones.
- Monitor your body: Pay attention to how your body reacts after consumption, especially concerning digestive issues or allergic symptoms.
- Choose wisely: If you are concerned about vitamin K2, some nattokinase supplements offer vitamin K2-removed versions, though the food itself contains it naturally.
Conclusion of Risks
In summary, the risks associated with eating natto are manageable and most often apply to people with specific health concerns. The most critical risk is its interaction with blood-thinning medication. By being informed and consulting a healthcare professional when necessary, individuals can enjoy this nutritious food while mitigating potential risks effectively. For the majority of the population, the health benefits of moderate natto consumption outweigh the potential negatives.
