Traditional Japanese Natto
Quick answer
A medium portion of Traditional Japanese Natto (50 g) contains 106 kcal, with 4.3 g of net carbohydrates and 9 g of protein. Its glycemic index is 25 (Low) for how fast it raises blood sugar, while its glycemic load per portion is 1.1 (Low) for its actual effect.
- Carbs7 g24.7%
- Protein9 g31.7%
- Fat5.5 g43.6%
- Fibre2.7 g
Percentages of total energy (calories)
Natto is one of the most divisive and admired fermented foods in the world. Whole soybeans are fermented with a beneficial bacterium called Bacillus subtilis, giving a sticky texture with stretchy strands and a pungent smell reminiscent of aged cheese. Behind that strong flavour lies one of the secrets of Japanese cuisine: natto is one of the richest dietary sources of vitamin K2 (the long-acting MK-7 form). Vitamin K contributes to the maintenance of normal bones and to normal blood clotting, and research is studying its role in directing calcium to bone rather than to blood vessel walls, although that evidence is still developing.
💡 Smart Nutritional Guidance
Consumption advice
One 45 to 50g pot two or three times a week gives you plenty of vitamin K2 and live bacteria that support colon health.
Best preparation methods
Natto is traditionally eaten uncooked to preserve the beneficial bacteria. Whip the beans with chopsticks in fast circles 50 to 100 times until sticky white strands form, then add a few drops of soy sauce and Japanese mustard and eat it over warm rice or with avocado.
Important Nutritional Note
Natto contains very large amounts of vitamin K, so people taking the blood thinner warfarin (Coumadin) should not eat it without their doctor’s advice: vitamin K weakens the drug’s effect and raises the risk of clots. It is made from soy, so avoid it if you have a soy allergy.
Nutrition facts
| Nutrient | Per 100 g | Per typical portion (50 g) |
|---|---|---|
| Calories | 212 kcal | 106 kcal |
| Protein | 18 g | 9 g |
| Carbohydrate | 14 g | 7 g |
| Available carbohydrate | 8.6 g | 4.3 g |
| Fat | 11 g | 5.5 g |
| Dietary fibre | 5.4 g | 2.7 g |
The typical portion is approximate, for comparison purposes.
Comparison & smarter alternatives
Among the foods in Asian dishes with a glycemic index (33), it ranks 5 (lowest first).
Smart alternatives from the same family:
Frequently asked questions
Is Traditional Japanese Natto good for weight loss?
It can be a useful part of a weight-loss plan because it provides 8.5 g of protein per 100 kcal, and protein supports fullness. A 50 g portion gives 106 kcal.
How does Traditional Japanese Natto affect blood sugar?
Its glycemic index is 25 (Low), a clinically reviewed estimate rather than a laboratory measurement. A typical 50 g portion has a glycemic load of 1.1 (Low), so the effect of this portion on blood sugar is limited.
What is the nutritional value of a typical portion of Traditional Japanese Natto?
A typical 50 g portion of Traditional Japanese Natto provides about 106 kcal, 9 g protein, 7 g carbohydrate, 5.5 g fat and 2.7 g fibre.
Why do doctors advise against natto with warfarin and other blood thinners?
The large amount of vitamin K in natto counteracts the way warfarin works in the liver. This can weaken the drug’s ability to prevent blood clots and cause serious complications, so ask your doctor before adding natto if you take any blood thinner.
Does natto help digestion and colon health?
It may. The spores of the fermenting bacterium (Bacillus subtilis) can survive stomach acid and reach the gut, and natto is a source of fibre (5.4g per 100g). Both support a diverse microbiome and regular bowel movements.
How does natto affect blood sugar and insulin resistance?
Its glycemic index is low (25) and the glycemic load of a 50g pot is only about 1.1. Its protein and fibre also slow absorption, which makes it a good choice for people with diabetes.
Read also
- Prediabetes: How to Stop the Train and Lower Your HbA1cGuide
- Gestational Diabetes Guide: Normal Levels and Foods to EatGuide
References & Scientific Sources
- The glycemic index of this food is a clinically reviewed estimate by the WiBo Health medical team, not a laboratory measurement from the International GI Tables (Atkinson 2021). GI bands (low ≤ 55 · medium 56–69 · high ≥ 70) follow: ISO 26642:2010. Food products — Determination of the glycaemic index (GI) and recommendation for food classification. International Organization for Standardization; 2010. www.iso.org/standard/43633.html
- Definition of available carbohydrate and glycemic load: FAO/WHO. Carbohydrates in human nutrition: report of a joint FAO/WHO expert consultation. FAO Food and Nutrition Paper 66. Rome; 1998. www.fao.org/4/w8079e/w8079e00.htm
Reviewed by the WiBo Health medical team · Last reviewed 13 October 2026
Disclaimer: This guidance is for nutritional lifestyle orientation and does not constitute a diagnostic medical device under EU Regulation MDR 2017/745.