Contents
What it is
Black soybean is the collective name for soybean varieties with a black seed coat. In Korea the main ones are seoritae, which is green inside, and the small round seomoktae. They are a different species from the black turtle beans used in Latin American cooking. Being soybeans, they carry more protein and fat than common beans. The black of the coat comes from anthocyanin. They are cooked into rice, simmered in soy sauce, blended into cold soy noodle broth or stir-fried, and are normally soaked first.
Scientific name Glycine max
In Korea, black soybeans are firmly established as a "food for hair". The reasoning offered is that hair is made of the protein keratin, and black soybeans are rich in protein and cysteine.
The logic is not wrong in itself. But there is no clinical evidence that adding protein improves hair in someone who is not protein-deficient. Black soybeans being a good food and black soybeans treating hair loss are separate claims.
Key benefits
- Nutrition data
Exceptionally rich in plant protein
34 g per 100 g dried, on par with yellow soybeans. Soy protein contains all the essential amino acids, making it one of the few plant foods that comes close to a complete protein.
- Nutrition data
Anthocyanins in the skin provide antioxidant activity
The black colour comes from the same family of anthocyanins as blueberries. That pigment is the real difference between black and yellow soybeans. Remove the skin and the advantage disappears.
- Nutrition data
Overwhelming in fibre
17 g per 100 g dried, a mix of soluble and insoluble, so it works on both the glucose response and bowel movement.
- Not established
It contains isoflavones
Like other soybeans, it carries the phytoestrogen isoflavones. Research on menopausal symptoms has run for years, but the Cochrane review concluded there is no conclusive evidence that phytoestrogen supplements reduce the frequency or severity of hot flushes and night sweats. Only genistein concentrates were left open as worth further study.[1]
How to eat it well
- Eat the skin. The anthocyanins are only there. The skin is the entire point of a black soybean.
- Soak at least eight hours before cooking. This reduces phytate and oligosaccharides and makes them easier to digest.
- Discard the soaking water. The gas-forming oligosaccharides dissolve into it.
- Black soybean tea carries almost no protein or fibre. If nutrition is the goal, eat the beans.
- Mixed into rice, they supply the lysine that rice lacks.
How to read the grades
Each benefit carries a label showing how far research on people supports it. Grades differ between items even within the same ingredient.
- Nutrition data
- A fact verifiable from food composition databases or health authorities. This is a different kind of statement from a clinical effect.
- Strong evidence
- Consistently confirmed across randomised controlled trials or meta-analyses.
- Moderate evidence
- Human studies exist, but effect sizes are small or results are mixed.
- Early research
- Cell or animal work, or small preliminary studies.
- Not established
- Commonly claimed, but not confirmed in studies on people.
What to watch out for
- Always cook them thoroughly. Undercooked beans contain lectins that impair digestion and cause gastrointestinal symptoms.
- Gas and bloating are common because of the oligosaccharides. Soaking and boiling reduce this considerably.
- With hypothyroidism and low iodine intake, large amounts of soy warrant caution.
- With gout, account for the purine content.
- Avoid entirely with soy allergy.
- If hair loss is ongoing, diagnosing the cause matters more than any food.
Nutrition
Per 100 g of dried black soybeans. Soaked and boiled they gain a little over twice their weight, so the amount cooked into rice or simmered in soy sauce corresponds to less dry weight than this table. These are a different species from the black turtle beans of Latin American cooking.
- Calories
- 382 kcal19%
- Protein
- 34.3 g69%
- Carbohydrates
- 30.4 g11%
- Fiber
- 17 g61%
- Fat
- 18 g23%
- Folate
- 281 µg70%
- Magnesium
- 252 mg60%
- Iron
- 7.7 mg43%
- Zinc
- 3.7 mg34%
Percentages are of the US FDA Daily Value for adults and children 4 and over. National reference intakes differ by sex and age.
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Sources
The databases and health authorities this article's nutrition figures and health statements draw on.
- 1Phytoestrogens for menopausal vasomotor symptomsMeta-analysisLethaby A, et al. Cochrane Database Syst Rev 2013PMID 24323914
- 2MFDS Food Composition Database · 식품안전나라Food composition database
- 3USDA FoodData CentralFood composition database
- 4NIH Office of Dietary SupplementsHealth authority
- 5PubMedResearch literature
