Natto: The Fermented Soy Superfood for Bone Health

Natto, a traditional Japanese dish made from fermented soybeans, has gained attention in recent years as a superfood with impressive health benefits, particularly for bone health. This sticky, pungent delicacy is rich in nutrients and contains unique compounds that may help prevent osteoporosis and reduce the risk of fractures. Let's explore the science behind natto's bone-boosting properties and how to incorporate this fermented food into your diet.

What is Natto?

Natto is made by fermenting cooked soybeans with a specific strain of bacteria called Bacillus subtilis var. natto7. The fermentation process breaks down the proteins and carbohydrates in the soybeans, creating a sticky, stringy texture and a distinctive odor often compared to aged cheese19. Natto is typically served over rice and seasoned with soy sauce, mustard, or green onions19.

In Japan, natto is a popular breakfast food and is widely consumed for its potential health benefits18. While its strong flavor and slimy consistency may be an acquired taste for some, natto enthusiasts appreciate its unique taste and texture18.

Nutritional Profile of Natto

Natto is a nutrient-dense food, packed with protein, fiber, vitamins, and minerals. A 100-gram serving of natto provides6:

• 19 grams of protein

• 5 grams of fiber

• 11 grams of fat

• 13 grams of carbohydrates

• 217 mg of calcium (17% DV)

• 7.5 mg of iron (48% DV)

• 1.1 mg of copper (74% DV)

• 115 mcg of vitamin K (19% DV)

Natto is also a good source of magnesium, potassium, zinc, and selenium6. The fermentation process enhances the bioavailability of these nutrients, making them easier for the body to absorb6.

Natto and Bone Health

Several studies have investigated the relationship between natto consumption and bone health, particularly in postmenopausal women who are at higher risk for osteoporosis.

Reduced Bone Loss

A Japanese population-based study found that postmenopausal women who consumed natto regularly had significantly reduced bone loss in the femoral neck and radius compared to those who did not eat natto5. The protective effects were more pronounced in older women, with those in their 70s experiencing 0.5% bone loss per year when consuming natto more than four times per week, compared to 1.8% bone loss per year in those who did not eat natto3.

Researchers suggest that the bone-protective effects of natto may be attributed to its high content of menaquinone-7 (MK-7), a form of vitamin K2, and bioavailable isoflavones5. These compounds are more abundant in natto than in other soybean products5.

Improved Bone Mineral Density

A meta-analysis of prospective studies found that natto consumption significantly improved lumbar spine and femoral neck bone mineral density (BMD) in perimenopausal women17. However, the effects on hip joint BMD were not significant17.

The authors suggest that the differences in results may be related to anatomical variations between tissues and the ethnic backgrounds of the study participants17. More large-scale, high-quality randomized controlled trials are needed to clarify the effects of natto on osteoporosis prevention17.

Reduced Fracture Risk

A large prospective cohort study in Japan revealed that habitual natto intake was associated with a reduced risk of osteoporotic fractures in postmenopausal women, independent of BMD12. Women who consumed natto more than four times per week had a 51% lower risk of fractures compared to those who ate natto less than once per week12.

The researchers propose that the protective effects of natto against fractures may be due to its high content of MK-7 and bioavailable isoflavones, which are more abundant in natto than in other soybean products12.

How Natto Supports Bone Health

The bone-protective properties of natto are attributed to several key compounds:

Vitamin K2 (MK-7)

Natto is one of the richest dietary sources of menaquinone-7 (MK-7), a highly bioavailable form of vitamin K24. Vitamin K2 plays a crucial role in bone metabolism by activating osteocalcin, a protein that binds calcium to the bone matrix4.

Studies have shown that MK-7 supplementation can improve bone strength and reduce the risk of fractures4. The high MK-7 content in natto may contribute to its bone-protective effects1.

Isoflavones

Soybeans, the main ingredient in natto, are rich in isoflavones, a type of phytoestrogen that mimics the effects of estrogen in the body5. Estrogen plays a key role in maintaining bone mass, and its decline during menopause can lead to accelerated bone loss5.

Natto contains higher levels of bioavailable isoflavones, particularly isoflavone aglycones, compared to other soybean products5. These compounds may help reduce bone loss and improve bone mineral density in postmenopausal women5.

Probiotics

The fermentation process used to make natto produces beneficial bacteria, known as probiotics6. Probiotics have been shown to support gut health, immune function, and nutrient absorption6.

Some studies suggest that probiotics may also play a role in bone health by modulating the gut microbiome and reducing inflammation6. The probiotic content of natto may contribute to its overall health benefits.

Incorporating Natto into Your Diet

If you're interested in adding natto to your diet for its potential bone health benefits, here are some tips:

1. Start small: If you're new to natto, begin with a small portion (1-2 tablespoons) to get accustomed to its strong flavor and texture18.

2. Mix with rice: The traditional way to eat natto is over a bowl of steamed rice, which helps balance its pungent taste19.

3. Add seasonings: Natto is often seasoned with soy sauce, mustard, or green onions to enhance its flavor19.

4. Experiment with recipes: Natto can be incorporated into various dishes, such as sushi rolls, salads, soups, and stir-fries19. Look for recipes online or in Japanese cookbooks.

5. Choose high-quality natto: Look for fresh, organic natto in Japanese grocery stores or online retailers. Avoid frozen natto, as it may have reduced health benefits18.

Remember, while natto may offer bone health benefits, it should be part of a balanced diet and healthy lifestyle that includes regular exercise, adequate calcium and vitamin D intake, and other bone-supporting nutrients.

Conclusion

Natto, a traditional Japanese fermented soybean dish, has emerged as a superfood with promising benefits for bone health. Its high content of vitamin K2 (MK-7), bioavailable isoflavones, and probiotics may help reduce bone loss, improve bone mineral density, and lower the risk of osteoporotic fractures, particularly in postmenopausal women.

While more research is needed to fully understand the mechanisms behind natto's bone-protective effects, incorporating this nutrient-dense food into your diet may be a tasty way to support your bone health. As with any dietary change, consult your healthcare provider to determine if natto is right for you.

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