Koya-dofu: Traditional Japanese Freeze-Dried Tofu Shows Promise for Obesity Prevention
Groundbreaking Research from Shinshu University Reveals New Health Benefits
In January 2025, 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.
Conclusion
Joint research by Shinshu University and Asahimatsu Foods has revealed that resistant protein in koya-dofu acts on intestinal bacteria to promote the production of GLP-1, the "slim hormone," effectively helping to prevent obesity and fatty liver disease.
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!
References
- https://www.shinshu-u.ac.jp/zukan/cooperation/post-63.html
- https://newscast.jp/smart/news/8094373
- https://www.asahimatsu.co.jp/research-2.html
- https://www.shoku-do.jp/column/co_0167_kouyatofu/
- https://www.imarcgroup.com/japan-fermented-superfoods-market
- https://www.japanhousela.com/articles/japan-the-land-of-fermentation/
Reactions in Japan
I'm amazed that koya-dofu can increase the slim hormone! My grandmother always said 'koya-dofu is good for your health,' and it turns out she was right. I'm going to start including it in my daily meals.
I'm so happy to see our local specialty being scientifically validated! Thank you to Shinshu University and Asahimatsu for this research. I'm proud as a Nagano resident.
The finding that resistant protein promotes GLP-1 production is very interesting. However, since this is still at the mouse experiment stage, I'd like to wait for further research on effects in humans.
GLP-1 diets are trending, but it's amazing that we can boost the same hormone with koya-dofu without relying on medication! I'm happy to lose weight naturally. Already searching for koya-dofu recipes! 🔍
I always get flagged at my metabolic health checkups, but maybe eating koya-dofu daily could help? I wish there were more recipes besides simmered dishes so it's easier to keep up...
It's premature to apply mouse experiment results directly to humans. It's not as simple as 'eat koya-dofu and lose weight.' Don't forget that a balanced diet and exercise are fundamental.
Koya-dofu isn't just for simmered dishes! You can grind it into powder for hamburgers, use it in sandwiches - the possibilities are endless. I hope this news helps more people discover koya-dofu's appeal.
Koya-dofu is high protein, low carb - the ultimate food for gym lovers. And now it turns out it promotes fat burning too? That's incredible. Maybe I'll use powdered koya-dofu instead of protein powder 💪
This could really energize the koya-dofu market. Younger generations don't eat much koya-dofu anymore, but scientific evidence of health benefits makes it easier to market. Great hints for product development.
I've loved koya-dofu since I was young and have eaten it regularly. Maybe that's contributed to my health. I want to continue cherishing traditional Japanese foods.
Koya-dofu has a long shelf life and is cheap - perfect for living alone. I was buying it to save money, but if it's healthy too, that's killing two birds with one stone!
It's hard to find koya-dofu overseas... Even Asian grocery stores rarely carry it. I hope this kind of news spreads so it becomes available abroad too.
Plant-based protein with fat-burning effects is great news for me as a vegan! This is more evidence that you can lose weight healthily without eating meat 🌱
I understand it's healthy, but I really can't stand that unique texture... Maybe powdered koya-dofu won't bother me? I might give it a try.
It's fascinating to see the health benefits of traditional Japanese foods being scientifically revealed. What's next? Natto? Umeboshi? You can really feel the power of Japanese cuisine.
What fascinating research! GLP-1 diet drugs are big news in the US, but if we can get the same effect from natural food, that's so much better. I'd love to try koya-dofu!
In Germany, we love fermented sauerkraut, but Japanese preserved foods like koya-dofu are fascinating too. High protein and long shelf life - perfect for emergency food storage, don't you think?
Japanese food is hugely popular in Singapore. Health-conscious people here are already into miso and natto. I'd be thrilled if koya-dofu became available in our supermarkets!
In France, we cherish our food traditions, but there's much to learn from Japanese traditional foods too. It's wonderful that a food with 800 years of history is being validated by modern science.
Obesity is a major social issue in Australia too. If we can improve through diet without relying on medication, that's the best approach. I'll look for koya-dofu!
As a Korean-American nutritionist, I find this research interesting, but we should be cautious about applying mouse study results to humans. That said, the research direction is promising.
Soy products aren't very common in Mexico, but if they have health benefits, it seems worth trying. Maybe I'll look for it at a Japanese restaurant.
Russia has dishes with frozen tofu too, but we haven't researched health benefits like with koya-dofu. I'm impressed by the seriousness of Japanese food research.
Demand for vegan foods is growing in the UK too. If a plant protein can help prevent obesity, koya-dofu might become the next superfood.
There are many Japanese grocery stores in Toronto, Canada, so koya-dofu is easy to find here. This research has motivated me to incorporate it more into my diet!
Japanese products are highly trusted in Hong Kong. If traditional foods like koya-dofu are scientifically proven effective, they'll surely become popular here.
Brazil produces a lot of soybeans, but processed foods like koya-dofu aren't well known here. I'd like to pay attention to this as a new way to use soybeans.
There's strong interest in sustainable foods in the Netherlands. Koya-dofu is shelf-stable and environmentally friendly as a plant protein source.
Japanese food is becoming more popular in New Zealand too. But koya-dofu isn't well known yet, so this kind of information is valuable.