How Many Calories in Natto? Nutrition Facts & Macros

Natto has 211 calories per 100 g. A typical Japanese serving of 45 g contains about 95 kcal with 8.7 g protein, 5 g fat, and only 3.3 g net carbs. The calorie content comes primarily from protein and fat, with fermentation improving bioavailability of nutrients compared to unfermented soybeans.

Natto is the richest known natural source of vitamin K2 in the MK-7 form. Unlike vitamin K1 (found in leafy greens), MK-7 has a long half-life and is highly bioavailable. It activates osteocalcin (directing calcium into bones) and matrix GLA protein (preventing calcium from depositing in arteries). Studies link regular MK-7 intake to improved bone density and reduced arterial stiffness. A single 45 g serving of natto can provide several hundred micrograms of MK-7.

Natto has a strong, distinctive flavor that is an acquired taste for many. It is savory and umami-rich with slightly nutty and earthy notes. The texture is sticky and stringy — the beans are connected by long, stretchy threads of fermentation byproducts. Traditionally served over hot rice with soy sauce and mustard, which balances the intensity. Start with a small amount mixed into rice if you are new to natto.

Both are soy-based, but they differ significantly. Natto is made by fermenting whole soybeans with Bacillus subtilis, producing probiotics, nattokinase, and vitamin K2. Tofu is made by coagulating soy milk into curds — no fermentation, no K2, no nattokinase. Nutritionally, natto has more protein (19.4 vs ~8 g), more fat (11 vs ~4 g), and far more iron (8.6 vs ~1.6 mg per 100 g). Natto also has more bioavailable minerals due to fermentation reducing phytates.

Nattokinase is a fibrinolytic enzyme naturally produced during natto fermentation. It has been studied for its ability to break down fibrin, a protein involved in blood clot formation. Research suggests it may support cardiovascular health by promoting healthy blood flow and reducing clot risk. Nattokinase is also sold as a supplement, but whole natto provides additional benefits: probiotics, vitamin K2, and complete protein. Consult a doctor before combining with blood thinners.

The most traditional way is over hot steamed rice with soy sauce and karashi mustard, stirring vigorously to increase the stringy texture. You can also add it to miso soup, mix into pasta, spread on toast, use in sushi rolls (natto maki), or blend into smoothies to mask the texture. For beginners, start with a small amount mixed into a strongly flavored dish. Natto is typically eaten at breakfast in Japan but works as a protein-rich addition to any meal.