The Potential Benefits of Natto for Fatty Liver
Fatty liver disease, or hepatic steatosis, is characterized by an excessive accumulation of fat in the liver. While lifestyle and dietary changes are primary management strategies, certain foods with therapeutic potential, like the Japanese superfood natto, are gaining attention. Fermented using Bacillus subtilis natto, this sticky soybean product is rich in several compounds that have shown promise in preclinical studies for mitigating aspects of fatty liver disease.
The Role of Nattokinase in Lipid Metabolism
One of the most well-known components of natto is nattokinase, an enzyme with potent fibrinolytic properties typically studied for cardiovascular benefits. However, nattokinase also exerts a lipid-lowering effect by regulating key enzymes involved in lipid metabolism. This can help reduce the levels of serum total cholesterol (TC), triglycerides (TG), and low-density lipoprotein cholesterol (LDL-C). Animal studies on hyperlipidemic mice have confirmed that natto treatment can significantly reduce serum lipid levels and improve overall metabolic profiles. By directly acting on lipid pathways, nattokinase may reduce the burden of fat accumulation on the liver.
Vitamin K2's Effect on Hepatic Steatosis
Natto is an exceptional source of vitamin K2, particularly the menaquinone-7 (MK-7) form, which is produced during the fermentation process. Recent animal studies have shown vitamin K2 can be protective against non-alcoholic fatty liver disease (NAFLD). A 2024 study on mice with diet-induced NAFLD found that supplementation with vitamin K2 significantly reduced hepatic steatosis (fat accumulation) and liver inflammation. The mechanism may involve the vitamin's ability to improve lipid metabolism and correct cholesterol synthesis disorders.
Probiotics and the Gut-Liver Axis
The gut-liver axis refers to the bidirectional relationship between the gut microbiota and the liver. Alterations in gut flora are linked to NAFLD progression. As a fermented food, natto is a rich source of Bacillus subtilis natto, a probiotic that can modulate gut microbiota composition. Research suggests that regulating gut microbiota with probiotics can have a protective effect on the liver. A study found that high-γ-PGA natto significantly altered the intestinal microbiota and decreased liver lipid content in mice, suggesting it could be a beneficial dietary component for NAFLD prevention.
Anti-inflammatory and Antioxidant Properties
Chronic inflammation and oxidative stress are key drivers in the progression of fatty liver disease. The compounds in natto, including soy isoflavones and nattokinase, have documented anti-inflammatory and antioxidant properties. By helping to combat inflammation, natto may mitigate liver damage and slow disease progression. For instance, nattokinase has been shown to downregulate pro-inflammatory markers in animal models. Soy isoflavones have also been linked to reduced oxidative stress and inflammation markers in human studies.
Comparison of Natto's Effects in Animal vs. Human Studies
| Aspect | Animal Studies (Preclinical) | Human Studies (Clinical) |
|---|---|---|
| Hepatoprotective Effects | Several studies show B. subtilis natto or its extract reduces hepatic fat, improves histology, and lowers liver enzymes in mice and rats. | Robust human clinical evidence specifically for natto's effect on NAFLD is limited or lacking. Broader evidence for soy products exists. |
| Lipid Regulation | Consistently demonstrates reduced total cholesterol and triglycerides. | Some evidence suggests soy products can improve blood lipid profiles in patients with NAFLD. Specific natto studies in humans are scarce. |
| Gut Microbiota Modulation | High-γ-PGA natto shown to alter gut microbiota composition and correlate with reduced liver lipids. | Modulating gut microbiota with probiotics is a documented strategy for NAFLD, but specific clinical data for natto is sparse. |
| Safety Profile | Generally shown to be safe in preclinical toxicity assessments. | Considered safe for consumption, but potential interactions, especially with blood thinners due to high Vitamin K2, require caution and medical supervision. |
How to Incorporate Natto into a Liver-Healthy Diet
If you are considering adding natto to your diet to support liver health, here are some tips:
- Start with Small Portions: Begin with a small amount, such as one tablespoon, to get accustomed to its unique flavor and sticky texture.
- Mix It Up: Natto is often served with soy sauce and mustard, but you can also mix it with rice, vegetables, or add it to soups to make it more palatable.
- Watch the Sodium: Be mindful of the high sodium content in some sauce packets often included with natto. Opt for a low-sodium soy sauce or use other seasonings.
- Pair with Other Healthy Foods: Consume natto as part of a balanced diet rich in whole grains, fruits, vegetables, and lean proteins to get the maximum benefit for liver health.
- Consult a Professional: Always speak with a healthcare provider or a registered dietitian before making significant dietary changes, especially if managing a health condition like fatty liver disease.
Important Considerations and Who Should Be Cautious
While natto offers promising benefits, it's not suitable for everyone. Its high concentration of vitamin K2 and nattokinase can have significant effects, especially for those with pre-existing conditions or taking specific medications.
- Blood-Thinning Medication: Individuals on blood thinners like warfarin must avoid natto or consult their doctor. Vitamin K2 can interfere with these medications and cause complications.
- Soy Allergies: As a fermented soybean product, natto should be avoided by anyone with a soy allergy.
- Excessive Amounts: While natto is nutritious, consuming extremely large amounts without medical guidance is not recommended, especially for those with liver conditions.
Conclusion
In summary, preclinical research suggests that natto contains several bioactive components, such as nattokinase, vitamin K2, and probiotics, that could positively impact fatty liver disease. These components may improve lipid metabolism, reduce fat accumulation, and exert anti-inflammatory and antioxidant effects. However, robust clinical evidence in humans remains limited, and further research is needed to confirm these findings. Natto should be viewed as a potentially beneficial dietary addition rather than a treatment or cure for fatty liver disease. For those without contraindications, incorporating moderate amounts of natto into a healthy, balanced diet may be a supportive strategy for liver health, but medical advice is always essential before making significant dietary changes.
Visit Frontiers in Pharmacology to read more about preclinical evidence for soy treatment of NAFLD
