How Does Natto Affect the Liver? A Scientific Overview

November 14, 2025 •

4 min read

Recent preclinical studies have investigated the impact of natto, a traditional Japanese fermented food, on liver health, suggesting it may positively affect lipid metabolism and hepatic fat accumulation. This review offers a scientific overview of how does natto affect the liver, exploring its beneficial components and mechanisms.

Quick Summary

Natto contains bioactive compounds like nattokinase, vitamin K2, and gamma-polyglutamic acid that may benefit liver health. Research suggests it can help regulate lipid metabolism, reduce hepatic fat accumulation, and decrease inflammation, potentially mitigating non-alcoholic fatty liver disease (NAFLD) and improving overall function. Its probiotic effects also modulate gut microbiota, which further supports liver function.

Key Points

Reduces Liver Fat: Preclinical studies show natto consumption can significantly reduce liver lipid and triglyceride content, inhibiting fat accumulation and mitigating fatty liver disease.
Decreases Inflammation: Bioactive compounds in natto, including nattokinase, have anti-inflammatory effects that can protect liver tissue from damage caused by chronic inflammation.
Modulates Gut Microbiota: The probiotic Bacillus subtilis var. natto can improve the gut microbiome, which positively influences the gut-liver axis and supports better metabolic function.
Rich in Vitamin K2: Natto is a superior source of vitamin K2, which contributes to overall health and has potential anti-inflammatory benefits relevant to the liver.
Enhances Lipid Metabolism: By promoting fatty acid catabolism and affecting lipid-related genes, natto's components help regulate lipid metabolism in the liver.
Preclinical Evidence: The evidence for natto's liver benefits is primarily from animal and in vitro studies; more human trials are needed to confirm these effects in humans.

Natto's Nutritional Profile and Key Bioactive Components

Natto's unique health benefits, particularly concerning the liver, stem from its rich composition, a product of fermenting soybeans with Bacillus subtilis var. natto. The fermentation process unlocks a range of powerful bioactive compounds.

Nattokinase

Nattokinase is a potent enzyme produced during the fermentation process that is widely recognized for its fibrinolytic activity, meaning its ability to break down blood clots. While its primary fame is related to cardiovascular health, it also supports liver health indirectly by improving blood flow and reducing overall inflammation. Studies in rat models have even shown that nattokinase can reduce specific markers of liver injury, such as alanine transferase (ALT) and aspartate aminotransferase (AST), after exposure to toxins.

Vitamin K2 (Menaquinone-7)

Natto is an exceptionally rich source of vitamin K2, specifically menaquinone-7 (MK-7), a form that is highly bioavailable. Vitamin K2 plays a crucial role in regulating calcium metabolism and bone health. While less known for its hepatic effects, some studies have explored its potential anti-inflammatory properties, which may benefit the liver.

Probiotics and Gamma-Polyglutamic Acid

Bacillus subtilis var. natto acts as a potent probiotic, directly influencing the gut microbiome. The health of the gut is intricately linked to the liver through the gut-liver axis. A balanced gut microbiota can lead to reduced liver fat, less inflammation, and improved insulin sensitivity, all of which are critical for preventing and managing non-alcoholic fatty liver disease (NAFLD). The sticky, slimy substance of natto is primarily gamma-polyglutamic acid (γ-PGA), which has also been linked to improved lipid metabolism and a more favorable gut bacteria profile.

Scientific Studies on Natto's Liver Effects

Extensive research, primarily in preclinical animal models, sheds light on the mechanisms by which natto benefits the liver. While human clinical trials are limited, the data provides a strong rationale for its potential.

Reducing Hepatic Fat Accumulation

Multiple studies on high-fat diet (HFD) animal models show that consuming Bacillus natto significantly reduces fat accumulation in the liver. These studies confirm a decrease in liver lipids, triglycerides, and total cholesterol, and a reduction in the area occupied by fat droplets within the liver tissue. The mechanism involves inhibiting fatty acid synthesis and promoting the catabolism (breakdown) of fatty acids within liver cells.

Decreasing Liver Inflammation

Inflammation is a key factor in the progression of liver diseases like NAFLD. Animal studies indicate that natto and nattokinase can significantly reduce levels of proinflammatory factors like TNF-α. This anti-inflammatory effect helps protect liver tissue from damage caused by chronic inflammation and oxidative stress.

Modulating the Gut-Liver Axis

Natto's probiotic properties directly influence the gut microbiome, which is known to affect liver health. Research shows that natto consumption can increase the ratio of beneficial bacteria, such as Bacteroidetes, to Firmicutes, and boost the abundance of Verrucomicrobia. This change in gut microbiota composition can improve metabolic functions and reduce endotoxins, thus alleviating stress on the liver.

Comparison: Natto vs. Other Fermented Foods for Liver Health


Feature	Natto	Yogurt	Sauerkraut	Kombucha
Key Probiotic	Bacillus subtilis var. natto	Lactobacillus and Bifidobacterium species	Lactobacillus species	Diverse yeasts and bacteria
Unique Liver Compounds	Nattokinase, γ-PGA, Vitamin K2 (MK-7)	None specific to liver	None specific to liver	Organic acids
Research on Liver Fat	Strong preclinical evidence for reduction	Indirect benefits via gut health	Indirect benefits via gut health	Indirect benefits via gut health
Research on Liver Inflammation	Preclinical evidence for anti-inflammatory effects	Benefits via gut microbiota modulation	Benefits via gut microbiota modulation	Potential anti-inflammatory properties
Primary Function	Cardiovascular and liver support	Gut health, immune support	Gut health, Vitamin C source	Gut health, antioxidant source

How to Incorporate Natto for Liver Benefits

For those interested in adding natto to their diet for its potential liver benefits, here are some tips:

Start with a small amount. Natto has a strong, unique flavor and sticky texture that can be an acquired taste. Begin with a small portion and increase gradually.
Mix it with rice. The traditional Japanese method is to mix natto with rice, which can make the taste more palatable.
Add other ingredients. Incorporate soy sauce, mustard, chopped scallions, or a raw egg yolk to enhance the flavor and texture.
Look for high-quality products. Ensure you are buying authentic fermented natto to get the full spectrum of its beneficial compounds.

It is important to note that while preclinical evidence is promising, it is not a substitute for medical advice or treatment for existing liver conditions. A holistic approach including a balanced diet and regular exercise is key. For more information on dietary management, consult reliable sources on liver health, such as the American Liver Foundation. [https://liverfoundation.org/]

Conclusion

Based on a growing body of preclinical evidence, natto, a traditional Japanese fermented food, shows promising effects on liver health. Its unique composition of nattokinase, probiotics, gamma-polyglutamic acid, and vitamin K2 contributes to its potential benefits. Studies indicate that natto can help reduce fat accumulation in the liver, decrease inflammation, and modulate the gut-liver axis by improving the gut microbiome. While human clinical trials are still needed to confirm these effects, incorporating natto into a balanced diet may offer protective and supportive benefits for the liver. Adopting healthy lifestyle habits remains the cornerstone of maintaining a healthy liver, and natto can be a valuable addition to this regimen.

The Role of Natto's Components in Liver Health

Nattokinase: A potent enzyme that may reduce inflammation and decrease markers of liver injury.
Probiotics: Contains Bacillus subtilis var. natto, which modulates gut microbiota and supports overall liver function.
Vitamin K2: An essential nutrient abundant in natto, contributing to overall health and potentially reducing inflammation.
Gamma-PGA: A sticky substance that improves lipid metabolism and promotes a healthy gut environment.
Soy Isoflavones: Found in the base soybeans, these have antioxidant and anti-inflammatory properties beneficial for liver health.

Frequently Asked Questions

Yes, preclinical studies suggest that natto can be beneficial for non-alcoholic fatty liver disease (NAFLD). Research in animal models indicates it helps reduce hepatic fat accumulation, decrease liver inflammation, and improve lipid metabolism.

Nattokinase is shown to reduce inflammation and blood lipids, which supports overall liver function. Studies in rats exposed to toxins demonstrated that nattokinase helped to lower liver enzyme levels like ALT and AST, indicating a protective effect.

The probiotic properties of natto introduce beneficial bacteria that modulate the gut-liver axis. A healthier gut environment leads to less inflammation and improved metabolic function, which directly benefits liver health and can help prevent conditions like NAFLD.

In some animal studies, nattokinase intervention effectively lowered elevated levels of liver enzymes such as ALT and AST, which are indicators of liver damage. However, these results are from animal models, and more research is needed for human application.

While natto is generally safe, it is extremely high in vitamin K2. Individuals on anticoagulant medication, such as warfarin, should consult a doctor before consuming large amounts, as vitamin K2 can interfere with medication. Moderate consumption as part of a balanced diet is recommended.

While natto contains compounds that support liver function by improving lipid metabolism and reducing inflammation, it is not a 'detox' food in the colloquial sense. The liver naturally detoxifies the body, and supportive foods like natto can help it perform optimally.

Natto's liver benefits come from several components working synergistically, including the enzyme nattokinase, the probiotic Bacillus subtilis var. natto, the probiotic-fermented gamma-polyglutamic acid (γ-PGA), and soy isoflavones.