Understanding Natto's Active Components
Natto is a fermented soybean product, and its primary active compounds are nattokinase and vitamin K2. Nattokinase is a powerful fibrinolytic enzyme known for its ability to dissolve fibrin, a protein that causes blood clotting. While this property is often promoted for cardiovascular health, it is precisely this action that makes natto risky for certain individuals. The fermentation process also produces significant amounts of vitamin K2, which plays a critical role in promoting blood clotting. This creates a complex interaction, especially for those on blood-modifying medication.
Who Should Avoid Natto?
For specific medical and health reasons, certain individuals should either refrain from eating natto or seek strict medical guidance before doing so. Ignoring these contraindications can lead to serious health complications.
Individuals on Blood-Thinning Medications
This is one of the most critical warnings regarding natto consumption. Individuals taking anticoagulants, or blood thinners, such as warfarin (Coumadin) or certain antiplatelet medications like aspirin and ibuprofen, should not take natto without a doctor's supervision.
- Risk: Natto's high vitamin K2 content can interfere with warfarin, a vitamin K antagonist, which can decrease the medication's effectiveness. Conversely, the nattokinase enzyme directly thins the blood, and combining it with other blood thinners can lead to an excessive anticoagulant effect, increasing the risk of serious bleeding and bruising.
- Action: Medical consultation is essential to manage dosage and monitor blood clotting levels (like INR) if any intake of natto or nattokinase is being considered.
People with Bleeding Disorders
For those with pre-existing bleeding disorders, like hemophilia, consuming natto can exacerbate their condition. The fibrinolytic action of nattokinase can increase the risk of spontaneous bleeding episodes. Anyone with a condition that affects blood clotting should treat natto with extreme caution and follow medical advice.
Before and After Surgery
Due to its powerful blood-thinning effects, natto should be discontinued well in advance of any scheduled surgery. Medical professionals recommend stopping natto at least two weeks before a procedure to prevent excessive bleeding during and after the operation. This includes dental surgery and other minor procedures where bleeding is a risk.
Pregnant and Breastfeeding Women
There is currently insufficient research to confirm the safety of natto and nattokinase for pregnant and breastfeeding women. Given the potential for blood-thinning effects and the lack of data, healthcare providers recommend avoiding its use to stay on the safe side. It is best for women in these stages to consume only minimal amounts found in food, if any, and only under medical supervision.
Individuals with Soy or Natto Allergies
As natto is made from fermented soybeans, it is a definitive contraindication for anyone with a soy allergy. However, a more specific, and often delayed, allergy to natto itself exists. In these cases, the allergen is poly-gamma-glutamic acid (PGA), a component of the sticky substance produced during fermentation, which is different from typical soy allergens. Allergic reactions can be severe, including late-onset anaphylaxis, a potentially life-threatening condition.
People with Very Low Blood Pressure
Nattokinase has demonstrated the ability to lower blood pressure in some individuals. For people who already have low blood pressure (hypotension), consuming natto could cause blood pressure to drop to an unsafe level, leading to symptoms such as dizziness and fainting.
People with a History of Certain Medical Conditions
Caution is advised for individuals with a history of specific blood-clot-related issues, such as ischemic stroke or peptic ulcers, as the powerful thrombolytic effects of nattokinase could theoretically dislodge a clot and cause a new, serious event. Case reports have also documented adverse events following the replacement of prescribed anticoagulants with nattokinase supplements.
Children
Given the lack of safety data and research on the effects of nattokinase in younger populations, it is generally recommended that children avoid taking nattokinase supplements.
Comparison of Natto Food vs. Nattokinase Supplements
| Feature | Natto (Food) | Nattokinase (Supplement) |
|---|---|---|
| Vitamin K2 | High concentration, which promotes clotting and counteracts some blood thinners like warfarin. | Often removed during processing to avoid interference with warfarin. However, some still contain it. |
| Fibrinolytic Action | Present, but part of a complex food matrix. | Highly concentrated enzyme, creating a potent blood-thinning effect. |
| Allergens | Contains allergens like soy protein and poly-gamma-glutamic acid (PGA). | Can contain trace amounts of allergens, depending on the manufacturing process. |
| Medical Supervision | Crucial for individuals on blood-modifying medications due to vitamin K2. | Essential for anyone considering its use, due to potent blood-thinning effects. |
Final Recommendations
While natto offers notable nutritional benefits, its potent biochemical properties necessitate caution for several groups. Anyone on blood thinners, with bleeding disorders, a soy or natto allergy, or those who are pregnant or breastfeeding should consult a healthcare provider before consuming natto. The same applies before and after surgery. The rule of thumb is to treat natto with the respect its powerful properties command and never self-prescribe it as a medical treatment. For a list of drug interactions and side effects, visit the Memorial Sloan Kettering Cancer Center's page on nattokinase.
Conclusion
Understanding who should not take natto is crucial for preventing serious health complications. The fermented food's high levels of nattokinase and vitamin K2, while beneficial for some, pose significant risks for individuals on blood-thinning medication, those with bleeding disorders, and people with allergies. Consultation with a healthcare provider is paramount to safely navigate the dietary choices surrounding this unique superfood. Always prioritize informed decisions over untested health claims to ensure optimal nutrition and safety for your body.
