Black soybean benefits: how far does the hair claim actually go

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

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.

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.

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.

It contains isoflavones

Like other soybeans, it carries the phytoestrogen isoflavones. Research on menopausal symptoms has continued for years, but effect sizes vary widely between individuals and results are inconsistent.

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.

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.

Related ingredients

Grains & legumes