Calories in Natto: Nutrition and Serving Sizes

Natto provides about 211 calories per 100 g of prepared fermented soybeans, based on the USDA FoodData Central SR Legacy entry Natto, FDC 172443. The same reference records 19.4 g protein, 11 g fat, 12.68 g total carbohydrate and 5.4 g dietary fibre per 100 g. These are figures for natto itself, not the rice, mustard, soy sauce or seasoning sachet that may accompany it.

Natto is a traditional Japanese food made by fermenting cooked soybeans with Bacillus subtilis var. natto. Its distinctive aroma, sticky strands and fermented flavour make it different from tofu, tempeh and plain cooked soybeans. Serving sizes are often small, so choosing the right weight is more useful than assuming every pack contains 100 g.

Natto nutrition per 100 g

The USDA composition record provides the following reference values for edible natto. Numbers for a particular brand can be different because the soybeans, moisture and preparation vary.

Source: USDA FoodData Central, Natto, SR Legacy FDC 172443.

The carbohydrate figure is reported according to a United States database convention and includes fibre. European food labels normally report available carbohydrates separately from fibre, so do not directly equate the two formats. There is no need to add the fibre grams to the total carbohydrate figure a second time.

How many calories are in a portion?

These practical values use exactly 211 kcal, 19.4 g protein and 11 g fat per 100 g of natto. Portion weights refer only to the fermented beans. They exclude seasoning, rice and the package.

Calories = grams of natto × 2.11. For example, a 45 g pack of beans represents about 95 kcal and 8.7 g protein. A 50 g portion provides about 106 kcal. The differences between the rounded table values are normal arithmetic rounding, not separate laboratory measurements.

A small prepared container may be labelled 40 g, 45 g or 50 g, but packaging sizes are not universal. If it includes a sauce sachet, read whether the printed serving nutrition covers the entire assembled product or only the beans. Our guide to portion size versus serving size explains how to compare the labelled amount with what you actually eat.

Why natto is different from unfermented soybeans

Natto starts with soybeans, yet fermentation changes flavour, texture and some food components. The reference nutrient profile is for the finished fermented product. Using a generic dry-soybean entry would be incorrect because dry beans and hydrated cooked beans have dramatically different water contents.

Natto is not a concentrated protein powder. It combines protein with naturally present fat and carbohydrate. It also offers fibre, something many animal-based protein foods do not provide. For a meal you still need to consider vegetables, grains and other ingredients, rather than treating a 40–50 g pack as a complete meal by itself.

Edamame is a different product: it usually refers to immature green soybeans that are boiled or steamed, not the fermented mature beans used for natto. See calories in edamame for the appropriate comparison. The foods may be used in similar bowls but should have separate diary entries.

Natto versus tofu and tempeh

These three soy foods are not interchangeable in either texture or nutrition. Tofu is made by coagulating soy milk, so its water content and fat and protein values depend strongly on firmness. Tempeh typically contains fermented whole soybeans bound together into a firm cake; its method and final moisture differ from natto.

Natto, by contrast, consists of distinct sticky fermented beans. The USDA natto reference is therefore not a reliable substitute for calories in tofu or calories in tempeh.

Compare the exact products on a consistent 100 g basis and, even more importantly, compare the servings you actually eat. A 50 g natto pack and a 150 g tofu serving are different quantities. Check sodium from marinades and sauces separately: unseasoned natto can be low in sodium while a flavoured prepared pack may be much higher.

What do soy sauce and seasoning packets add?

Many natto products contain separate seasoning sachets such as soy sauce, mustard or a sweet savoury sauce. Their ingredients determine the extra energy and especially the sodium. The USDA table above does not automatically include these condiments.

For example, imagine 50 g natto (about 106 kcal) plus 10 g sauce with a hypothetical label value of 150 kcal per 100 g (15 kcal). Together that would be approximately 121 kcal. The sauce value is deliberately an example, not the composition of every natto seasoning packet. If your package provides separate nutrition information, use those figures instead.

The same calculation matters for sesame oil, mayonnaise or added sugar. Small amounts can change the total, and a sodium-restricted diet requires looking beyond the calories on the main natto entry. A packet labelled as one serving may contain several individually weighed components.

Example: natto served with rice

A simple bowl could contain 50 g natto, 150 g cooked rice and a 10 g seasoning sauce. The natto contributes approximately 106 kcal. If the specific cooked rice used is recorded at 130 kcal per 100 g, it contributes 195 kcal. If that sauce is recorded at 150 kcal per 100 g, it adds 15 kcal. Illustrative total: 316 kcal.

This is a worked example with clearly stated reference assumptions. Cooked rice values change with variety and water content; packaged sauces also vary. Substitute the actual label or database entry when tracking your own meal. Spring onion, egg, sesame seeds or additional oil must be counted if included.

The same principle applies if natto is mixed into noodles or placed on toast: record the fermented beans separately from the starches, toppings and dressings. A dish described as 'natto rice' does not have one universal calorie count.

Protein, fibre and minerals: what is meaningful?

A 50 g serving supplies about 9.7 g protein, 5.5 g fat and 2.7 g fibre from the USDA reference. Those values can contribute to a mixed diet, but they do not establish a special therapeutic benefit from a serving of natto.

The database lists potassium, calcium, iron and other minerals, but these values cannot replace a complete assessment of a person's dietary needs. Natto is made from soy, a major food allergen. Anyone with a diagnosed soy allergy should avoid it and check packaging and cross-contact warnings.

Claims that natto enzymes or fermentation by themselves prevent blood clots, reverse disease or produce weight loss are not supported by the calorie and nutrient measurements used here. Nutrient tables describe composition, not clinical outcomes.

Vitamin K and warfarin: important precaution

Natto can be a significant dietary source of vitamin K, particularly vitamin K2 forms associated with fermentation. Nutrient content varies by product and testing method, so an old composition table should not be interpreted as a precise vitamin K2 dose for every brand.

If you take warfarin, speak to your anticoagulation clinic or prescriber before eating natto or making a change to your regular intake. Vitamin K-rich foods can alter the drug's effect and your INR monitoring requirements. Do not stop or adjust prescribed medication based on a food article. The Cambridge University Hospitals guidance for patients taking warfarin specifically includes natto among fermented foods to discuss.

This warning applies to warfarin management; it must not be generalized automatically to every anticoagulant, which can have different dietary interaction rules.

Choosing, storing and tracking natto

In many shops natto is sold chilled or frozen in small packs. Check the use-by instructions, storage temperature and whether the package has been thawed. Follow the manufacturer's handling directions and discard food that is spoiled or outside safe storage conditions. Fermentation is a production process, not a guarantee that any opened package will keep indefinitely.

For a calorie log, weigh or read the actual quantity of fermented beans, select natto rather than generic soybeans, then enter included sauces and other toppings separately. Use a product label over a generic USDA reference when the formulation differs. This avoids confusing natto with miso paste, tofu or a soy-based ready meal.

Sources and calculation limits

• USDA FoodData Central — Natto, SR Legacy FDC 172443.
• Cambridge University Hospitals — dietary advice for patients taking warfarin.

Portions and meal totals are arithmetic examples based on stated input weights. Natto nutrients vary with fermentation, soybeans and commercial formulation; the values do not establish medical effects.