How much barley do you need to make a keg? I'm sure once you make some, you can save a little and never have to buy more yeast, unless you are affraid of pathogenic stuff taking over and just want to start fresh each time. You could save money. All these people spending money on beer just don't know what they are doing. But most of them won't even stock up on beer before 2AM, so they run out or have to make a mad dash to the local convenience store at 2AM, so of course they won't bother waiting a month.
I just read on nutritiondata.com that natto does not have nearly as much nutrition value as soy beans. Maybe the nutrition is more absorbable, but there is about 1/3 as much.