Natto's Nutritional Profile and Glycemic Impact
Natto is made by fermenting soybeans with the bacterium Bacillus subtilis. This process significantly enhances the nutritional value of the soybeans, creating a food rich in protein, dietary fiber, vitamins, and beneficial enzymes.
Unlike non-fermented soybeans, the fermentation in natto produces compounds specifically beneficial for glycemic control. Its low glycemic index (GI) means it doesn't cause a rapid spike in blood sugar levels, a crucial factor for anyone managing diabetes. A study comparing meals with white rice and natto to white rice alone found that the natto meal significantly suppressed the rise in postprandial blood glucose levels.
The Role of Gamma-Polyglutamic Acid (γ-PGA) and Nattokinase
Two of the most important compounds in natto for managing diabetes are γ-PGA and nattokinase.
- Gamma-Polyglutamic Acid (γ-PGA): This viscous, sticky substance produced during fermentation is primarily responsible for suppressing postprandial blood glucose elevation. Research suggests that γ-PGA acts like a water-soluble dietary fiber, increasing the viscosity of contents in the small intestine. This action delays the digestion and absorption of carbohydrates, leading to a more gradual rise in blood sugar.
- Nattokinase: This potent enzyme has been extensively studied for its cardiovascular benefits, which are especially important for diabetics who are at higher risk for heart disease. Nattokinase helps dissolve blood clots by breaking down fibrin and can also help lower blood pressure, which lessens the strain on the heart. While known primarily for its impact on circulation, nattokinase also contributes to overall metabolic health.
Natto and Insulin Sensitivity
Insulin resistance is a key component of type 2 diabetes. Several studies indicate that natto can help improve insulin sensitivity. The probiotic properties of Bacillus subtilis in natto promote a healthier gut microbiome, and a balanced gut is linked to better metabolic health and improved insulin sensitivity.
One randomized, crossover study involving overweight individuals with impaired glucose tolerance found that consuming a breakfast including natto and viscous vegetables for two weeks improved insulin sensitivity. This effect was observed alongside a decrease in total and LDL-cholesterol levels. A separate study focusing on obese and diabetic participants over three months showed improved metabolic health, including better insulin sensitivity and lower HbA1c, regardless of weight loss.
Comparison: Natto vs. Plain Soybeans
To illustrate the unique benefits of fermentation, it is helpful to compare natto to regular, unfermented soybeans.
| Feature | Natto (Fermented Soybeans) | Plain Soybeans (Unfermented) |
|---|---|---|
| Effect on Postprandial Glucose | Significantly suppresses blood glucose spikes due to γ-PGA and fermentation. | Shows some effect on lowering glucose, but less pronounced than natto. |
| Presence of Nattokinase | Contains the potent enzyme nattokinase, absent in plain soybeans. | Does not contain nattokinase. |
| Probiotic Content | Rich source of beneficial Bacillus subtilis bacteria, promoting gut health. | Lacks probiotic bacteria, though it is a good source of fiber. |
| Bioavailability | Fermentation can increase the bioavailability of certain nutrients and bioactive compounds. | Nutrients are less readily absorbed compared to fermented versions. |
| Vitamin K2 Content | Exceptionally high in Vitamin K2 (menaquinone-7), crucial for bone and heart health. | Contains Vitamin K1, but not the more bioavailable K2 variant found in natto. |
Integrating Natto into a Diabetic Diet
For diabetics, incorporating natto can be a beneficial dietary strategy. Start with a small serving size, typically a half-pack to one full pack, mixed with a little soy sauce or other diabetic-friendly toppings like green onions. Pairing natto with foods that typically cause a blood sugar spike, such as white rice, can help mitigate that effect. As with any dietary change, consulting with a healthcare provider or a registered dietitian is recommended, especially for individuals on blood-thinning medication due to natto's high vitamin K2 content.
Precautions for Diabetics Considering Natto
While natto offers many benefits, it is not suitable for everyone. Individuals with a soy allergy should avoid it. The most significant caution is for those on blood-thinning medications like warfarin. Natto's high concentration of vitamin K2 can interfere with these medications and increase the risk of excessive bleeding. Always speak with a doctor before adding natto to your regimen if you are on such medication.
Conclusion
In conclusion, natto presents a compelling case as a functional food for managing diabetes. Its unique combination of a low glycemic index, the glucose-regulating compound γ-PGA, the cardioprotective enzyme nattokinase, and its rich probiotic content make it a powerful ally in supporting healthy blood sugar levels and overall metabolic health. While the pungent aroma and sticky texture can be an acquired taste, the science-backed benefits make it a worthy consideration for those seeking natural dietary support for their diabetic management plan, provided they address potential medication interactions with their doctor.
For an in-depth review on fermented soybean foods and diabetes, see the article on PMC.
