Nakao (1972) introduced the "natto triangle" of soyfoods, which included tempeh in Indonesia. The inclusion of Indonesia in the triangle was supported by Nakao's theory that natto came to Japan from Java. However, Shurtleff and Aoyagi's 2012 report on natto shows that extensive further research on the origin of nattō does not support this theory. Furthermore, tempeh is mold-fermented, whereas every other soyfood propagated and included in the KNT triangle is Bacillus-fermented.

While some older sources, especially news and magazine articles, continued to use the "natto triangle" including tempeh, a plurality of following papers have shown many soybean foods in the KNT triangle that follow that triangle's theory of bacterial origination and cultural propagation. In fact, it appears many Asian soyfoods may have originated from the same Bacillus stock. Meanwhile, no mold-fermented soybean foods have been found to originate in the KNT triangle. Overall, these factors undermine Nakao's original "natto triangle" theory. See Nakao (1986); Nagai and Tamang (2010); Shurtleff and Aoyagi (2012).

This map locates the primary Bacillus-based soyfoods in the KNT triangle discussed by Tamang (2010) and Tamang (2015). It excludes tempeh and other mold-based foods that modern research has shown to be developmentally and culturally unrelated. A minor modification from the Tamang diagrams is that I used "shuidouchi" instead of "douchi" – this better reflects what is described in the literature and clarified in Shurtleff and Aoyagi (2012). Shuidouchi is specifically a Bacillus-fermented soyfood originating in Southern China, whereas my understanding is that douchi alone can also refer to a different, mold-fermented food that should not be confused with shuidouchi.

Based on File:BlankMap-World-162E.svg (public domain). Thanks to Sacrificiallambda for help finding these sources and making the diagram.

Literature:

• Nakao, Susuke (1972) (in Japanese) Ryōri no kigen [The origin of foods], Japan: Nihon Hōsō Shuppan Kyōkai
• Nakao, Sasuke (1986) "Minzokugaku-sha to shite deatta koto domo [An ethnologist’s recollections (on fermented soyfoods)]" in Aida, Kô, ed. (in Japanese) Proceedings of the Asian Symposium on Non-Salted Soybean Fermentation, Japan: Takeshima Shigeru
• Tamang, Jyoti Prakash (2010) Himalayan fermented foods: microbiology, nutrition, and ethnic values, Boca Raton, Fla.: CRC Press/Taylor & Francis ISBN: 978-1-4200-9324-7.
• "Fermented Legumes: Soybean and Non-Soybean Products" in (2010) Fermented Foods and Beverages of the World, CRC Press, pp. 191–224 DOI: 10.1201/EBK1420094954-c6. ISBN: 978-1-4200-9495-4 978-1-4200-9496-1.
• Shurtleff, William; Aoyagi, Akiko (2012). History of Natto and its Relatives (1405–2012) (PDF). SoyInfo Center.
• Tamang, Jyoti Prakash (2015). "Naturally fermented ethnic soybean foods of India". Journal of Ethnic Foods 2 (1): 8–17. DOI:10.1016/j.jef.2015.02.003. ISSN 23526181.