The natto bacillus itself has also been found to regulate intestinal functions.
There are more than a billion natto bacteria in each gram of natto. As one individual serving package of natto contains around 45g, this works out to an intake of 45 billion natto bacteria into the body at each meal.

Probiotics is the word that is used to describe living microorganisms that improve the balance in the intestinal environment of a host and therefore have a beneficial effect on the host, as well as the foods that contain these microorganisms. It is possible that the natto bacillus and the food that contains it, natto, also constitute an excellent probiotic.

Various microorganisms establish themselves in our intestines and form complex groups. The modality of these groups is called the intestinal flora, and among these microorganisms the bacteria are referred to as intestinal bacteria.
Several hundred varieties of intestinal bacteria are known to inhabit the human intestine. The natto bacillus acts to maintain the balance of intestinal bacteria and inhibit the putrefactive bacteria that are said to be harmful bacteria.
The natto bacillus also has the potential to inhibit disease-causing bacteria such as salmonella and Pseudomonas aeruginosa.