Behind every public figure's appearance lies a personal health and beauty routine. This series examines the diets, exercise habits, treatments, and beauty and fashion choices of notable figures as practical lifestyle information.

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Sana of the K-pop group Twice has drawn attention after revealing she drinks black soybean milk every morning for her hair health. Black soybeans are widely regarded as beneficial for preventing hair loss, as they contain protein, iron and other nutrients involved in hair growth. But can consistently eating black soybeans actually make hair grow faster?

Sana introduced black soybean milk as one of her regular foods in a video published Tuesday on the YouTube channel GQ Korea. "When I was on the world tour, I drank black soybean tea and it seemed like my hair was growing faster," she said, adding that she now compares black soybean content across products and drinks a carton every morning.

Hair growth involves a range of nutrients, including protein and iron. Hair loss caused by nutritional deficiency can improve simply by replenishing the missing nutrients, making everyday dietary habits an important factor.

How do the protein and iron in black soybeans affect hair growth?

Hair is composed mostly of a protein called keratin, which maintains the strength and elasticity of each strand. An adequate supply of protein is needed for hair follicles to produce new hair.

When protein intake is insufficient, the body prioritizes delivering nutrients to organs essential for survival and may reduce the energy allocated to hair growth. Extreme dieting or prolonged caloric restriction in particular can lead to thinning and shedding when both protein and overall calorie intake fall short.

Black soybeans are rich in plant-based protein and supply the amino acids needed to build hair. They also contain minerals involved in hair health, including iron and zinc. Iron is a component of hemoglobin in the blood and plays a role in oxygen transport, while zinc is required for cell growth and protein synthesis.

The American Academy of Dermatology (AAD) says insufficient intake of protein, iron, zinc and biotin can contribute to hair loss. When nutritional deficiency is the underlying cause, hair growth can recover once the missing nutrients are replenished.

The link between nutritional status and hair loss has also been confirmed in large-scale research. A 2025 study on diet and hair health pooled data from 61,332 participants across 17 studies and found an association between lower levels of iron and vitamin D and higher rates of observed hair loss.

Hair growth rate is influenced by a combination of genetic factors, age, hormonal status and overall health. Scalp hair typically grows about 1 centimeter per month, and eating more of any particular food does not proportionally accelerate that rate.

Isoflavones in black soybeans and what the research actually shows

Another reason black soybeans are considered beneficial for hair health is a compound called isoflavone. Isoflavones are plant-based compounds found in soybeans that can partially mimic the action of estrogen in the body, which is why they are also referred to as phytoestrogens.

Hormones also play a significant role in hair growth. Some forms of male-pattern and female-pattern hair loss are influenced by genetic predisposition and the action of androgen hormones. Researchers have accordingly investigated how soy isoflavones affect follicle function and hair growth.

A study by Japanese researchers published in 2007 in the journal Growth Hormone & IGF Research found changes in hair growth when isoflavones and capsaicin — the compound responsible for the heat in chili peppers — were taken together.

The researchers conducted a five-month experiment with 48 adults experiencing hair loss. Hair growth promotion was observed in 20 of the 31 participants (64.5 percent) who took isoflavones and capsaicin together, compared with 2 of the 17 participants (11.8 percent) in the placebo group.

The researchers suggested the two compounds may have stimulated production of insulin-like growth factor 1, or IGF-1, which is involved in hair growth.

The study, however, involved a small number of participants and administered isoflavones and capsaicin together. Whether consuming ordinary black soybeans or soybean milk alone produces the same effect requires separate verification.

A 2023 review published in JAMA Dermatology also suggested that certain nutritional interventions — including those involving isoflavones and capsaicin — may help improve hair loss. The researchers reviewed 30 studies and said larger clinical trials are needed to more clearly establish the effects of nutritional components.

Anthocyanin, found in the dark outer skin of black soybeans, is also known for its antioxidant properties. The presence of antioxidant compounds alone does not mean they promote hair growth, however, and in actual hair loss treatment, a medical approach tailored to the underlying cause remains essential.

Protein content in black soybean milk can vary twofold — check the label

Anyone looking to drink black soybean milk consistently, as Sana does, would do well to examine the nutritional information on the label. Even among black soybean milk products, protein content, sugar levels and calorie counts can vary considerably depending on the proportion of raw ingredients, the manufacturing process and any added components.

According to a plant-based beverage quality comparison published by the Korea Consumer Agency in January this year, a survey of 11 commercially available products — including black soybean, oat and almond drinks — found that black soybean milk had the highest protein content among them.

Protein content in black soybean milk ranged from 4 to 9 grams per carton, a difference of more than twofold depending on the product. Calorie counts also varied, from 90 to 150 kilocalories, and the nutritional composition differed across plant-based drinks of the same volume depending on the ingredients used.

A higher stated black soybean content on the label does not necessarily mean higher protein content. The ratio of black soybean extract to regular soybean liquid differs by product, and some products contain added sugar or oligosaccharides.

When choosing soybean milk for hair health, it is therefore advisable to compare not only the black soybean content but also the actual protein content, sugar levels and calorie count. Those looking to reduce sugar intake may want to opt for unsweetened products.

There is also no need to rely solely on black soybeans for the nutrients hair requires. Eating a varied mix of protein-rich foods — such as eggs, fish, lean meat and tofu — alongside vegetables high in iron and vitamins is beneficial. The plant-based iron in soybeans is absorbed less efficiently than iron from animal sources, so pairing them with vegetables or fruits rich in vitamin C can also help.

If hair suddenly begins falling out in larger amounts or a part appears to be widening, it is important to assess both nutritional status and the underlying cause of the hair loss. Factors including anemia, thyroid conditions, hormonal changes and stress can all contribute, and treatment approaches vary depending on the cause.

Black soybean milk is a convenient source of protein and minerals that can be incorporated into everyday hair care. Maintaining adequate nutrition and a balanced diet remains the most fundamental approach to growing healthy hair.


rainbow@heraldcorp.com