In January 2026, a joint research project between Shinshu University School of Medicine and Asahimatsu Foods Corporation revealed that koya-dofu (freeze-dried tofu), a traditional Japanese preserved food, may help prevent obesity and fatty liver disease. The findings, published in the prestigious International Journal of Biological Macromolecules, have attracted significant attention from health-conscious consumers worldwide.

What is Koya-dofu? An 800-Year-Old Japanese Superfood

Koya-dofu is a preserved food made by freezing tofu, allowing it to mature at low temperatures for approximately three weeks, and then drying it. Its origins date back to Japan's Kamakura period (1185-1333), where it is said to have been accidentally discovered by monks at Mount Koya who used the winter cold to preserve their food.

Also known as "kori-dofu" (frozen tofu) or "shimi-dofu" (frost tofu), this traditional ingredient is particularly associated with Nagano Prefecture, which produces over 90% of Japan's total supply. In its dried state, koya-dofu has a firm, sponge-like texture. When rehydrated in water or dashi broth, it becomes soft and can be used in various dishes, from simmered preparations to salads. Its long shelf life, it can be stored at room temperature for over six months, has made it a valuable emergency food throughout Japanese history.

Research Overview: The Connection Between Resistant Protein and the "Slim Hormone" GLP-1

Research Team and Duration

This research was conducted by Professor Naoki Tanaka's team at Shinshu University's Academic Assembly (Medical Sciences) in collaboration with Takahiro Ishiguro, Deputy Chief Researcher at Asahimatsu Foods Corporation, headquartered in Iida City, Nagano Prefecture. The joint research began in 2020.

Experimental Methods and Results

The research team conducted a 16-week experiment using mice, feeding them four different diets:

  • Standard diet
  • High-fat diet
  • High-fat diet supplemented with koya-dofu protein
  • High-fat diet supplemented with resistant protein

The results showed that mice fed a high-fat diet gained an average of 10 grams more weight compared to those on a standard diet. However, mice given high-fat diets supplemented with koya-dofu protein or resistant protein showed weight gain limited to approximately 6 grams.

More significantly, the intestines of mice that consumed koya-dofu or resistant protein showed a marked increase in substances that produce "glucagon-like peptide-1" (GLP-1).

What is GLP-1?

GLP-1 is a hormone secreted by the small intestine, often called the "slim hormone" or "satiety hormone." It helps lower blood sugar levels and promotes fat breakdown, making it a valuable component in diabetes medications. In November 2023, "Wegovy," an anti-obesity medication that utilizes GLP-1 action, received insurance coverage approval in Japan, validating its effectiveness.

Professor Tanaka explains: "The resistant protein in koya-dofu likely acts on intestinal bacteria to increase metabolites that produce GLP-1."

The Remarkable Health Benefits of Resistant Protein

What is Resistant Protein?

Resistant protein refers to "indigestible protein" that, unlike regular protein, is difficult to digest in the stomach and small intestine. Approximately 30% of koya-dofu's protein content consists of resistant protein, with a remarkably high concentration of 10-25 grams per 100 grams of koya-dofu.

Why Koya-dofu Contains More Resistant Protein

The manufacturing process of koya-dofu naturally increases its resistant protein content. During the compression and freezing stages, protein bonds become stronger. Furthermore, the extended maturation period of approximately three weeks at around minus 2°C allows ice crystals to grow, forming even more resistant protein.

Expected Health Benefits

Resistant protein is associated with numerous health benefits:

  • Suppression of blood sugar spikes
  • Reduction of LDL (bad) cholesterol
  • Prevention of triglyceride elevation
  • Improvement of gut environment
  • Enhancement of immune function
  • Relief of constipation

The research also confirmed that there were no adverse effects on the stomach, kidneys, or heart, demonstrating koya-dofu's safety as a food product.

Why the World is Now Focusing on Japanese Fermented and Preserved Foods

Global Expansion of the Fermented Foods Market

The global fermented foods market is expanding rapidly, projected to reach approximately $258 billion in 2025 and $378 billion by 2032. The average annual growth rate stands at about 5.6%, with the Asia-Pacific region accounting for approximately 49% of the market.

The Gut Health Movement and Interest in Probiotics

As global health consciousness rises, interest in "gut health" and "probiotics" has spread rapidly. In China, approximately 48% of consumers cite probiotics as the number one ingredient for gut health. The digestive benefits and immune-boosting effects of fermented foods are highly valued worldwide.

Japanese Fermented Foods Going Global

Traditional Japanese fermented foods such as miso, natto, soy sauce, and koji are rapidly gaining recognition overseas. Miso, in particular, has seen 21% of new product launches in Europe, 16% in broader Asia (outside Japan), and 11% in North America, indicating significant global expansion.

Key reasons for the growing interest in Japanese fermented foods include:

  • Gut environment improvement through probiotics
  • Unique umami flavors
  • Rich source of plant-based protein
  • Healthy attributes: low calorie, low sugar
  • Alignment with sustainable food production

Global Recognition of Washoku

Washoku, registered as a UNESCO Intangible Cultural Heritage in 2013, is highly valued worldwide as a healthy food culture rich in fermented foods and dietary fiber. The washoku philosophy of balanced consumption of vegetables, fermented foods, and quality proteins perfectly aligns with modern health trends.

Future Developments and Possibilities for Koya-dofu

Deepening Research Through Medical-Agricultural-Industrial Collaboration

Professor Tanaka has expressed his desire to "add 'delicious' to 'healthy,'" showing enthusiasm for developing new food products such as hamburgers made with powdered koya-dofu. The "medical-agricultural-industrial collaboration" between Shinshu University's medical and agricultural faculties and Asahimatsu Foods is expected to accelerate research on koya-dofu's health benefits.

Application to Frailty Prevention

Asahimatsu Foods' Deputy Chief Researcher Ishiguro has indicated plans to expand koya-dofu's health applications beyond obesity prevention. There is particular interest in addressing "frailty" in elderly populations, a weakened state characterized by decreased muscle strength and vitality, through koya-dofu's abundant protein content and gut health benefits.

A Secret to Japanese Longevity

Japan is one of the world's leading longevity nations, and traditional food culture has long been cited as one of the secrets. As scientific health benefits of fermented and preserved foods like koya-dofu continue to emerge, global interest in Japanese cuisine is expected to grow even further.

Science Rediscovers a Traditional Food's Value

This traditional Japanese food with over 800 years of history is being rediscovered through cutting-edge scientific research, a key reason why Japanese fermented and preserved foods are attracting global attention. Koya-dofu has supported Japanese health since ancient times and will undoubtedly continue to be loved as a health food around the world.

In Japan, there has long been a saying that "koya-dofu is good for your body," and now science has proven this belief. Does your country have traditional foods that have been said to promote health since ancient times? We'd love to hear about your country's "superfoods" and traditional preserved foods!

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