Natto is made from only one ingredient: soybeans.
The fine threads extending from the beans are produced by the natto bacillus in the fermentation process. In general, they are made up of proteins (amino acids) and sugars, and they have been confirmed to promote the absorption of calcium.

Natto provides all of the highly nutritious components of soybeans, such as protein and lipids, as well as additional healthy components provided by the action of the natto bacillus (Bacillus subtilis var. natto).