Your gut relies on the presence of good bacteria — known as probiotics — to stay healthy and digest all the nutrients that you take in. Fortunately, seeing as natto is made from fermented soybeans, it will increase the number of good bacteria in your gut and thus provide an overall health boost when it comes to your microbiome. It’s worth noting that you shouldn’t eat soybeans that aren’t fermented as this can lead to various thyroid and hormone problems.
That being said, the fermented soybeans in natto and very safe. The boost in good bacteria can stave off various conditions. For instance, if you’re suffering from constipation then that likely means that you don’t have high enough numbers of good bacteria in your gut. Natto can remedy the situation by regulating the probiotic population in your microbiome. If you’re constipated then eat some natto rather than relying on OTC medications to artificially induce defecation.