Fermentation Support Forum

I have a bit of a love/hate relationship with natto. I thoroughly enjoy eating it, but I always get sick from it afterwards. I've made natto many different ways and each time I get sick in exactly the same way. I first feel a sort of pressure in my stomach and later my intestines constrict. I grow irritable, fatigued, and constipated for days.

I am always very careful to ensure that no contamination occurs during the fermentation process. I've used natto spores as a starter for some batches and frozen professionally made natto I bought for other batches. Some batches were made with normal sized soybeans, others with small type natto soybeans, and even garbanzo beans. The fermentation seems to go well, with slimy threads and all.

No matter which method I use to make natto, sickness is always the result. I can only conclude that I am intolerant to the bacteria used to make natto. Has anyone else experienced something similar? I am at my wits' end and about to completely give up on natto.

Have you involved your primary care doctor in diagnosing this issue? Does this happen only with the Natto you make or does it happen with all Natto such as the frozen professionally made natto you mention or Natto that you may haven eaten at a restaurant or Natto made by someone else? Have you had your Natto analyzed to see what it is that you are eating?

I feel sick after eating any kind of natto, whether it's my homemade natto or store bought. The natto I buy has less of an effect on me than my homemade natto, but I still feel sick after a few days of eating it. I've sourced natto from different places with the same effects which makes me think that it is the specific bacteria that natto is made with that I am sensitive to.

I do have IBS so that may be a factor. My body rejects many kinds of foods, but natto is the only fermented food that my body has rejected. I don't have any problems with miso, tempeh, kimchi, or kombucha.

For those who are interested, I have resolved the issue. The problem was that I was not steaming the soybeans in my Instant Pot long enough. I was only steaming around 1 hour 30 minutes. When I tried steaming the beans for 3 hours, they were much softer, almost paste-like but still held their shape well. The fermentation of these softer beans turned out much better and I had no digestion issues at all!

Presumably, the reason why my earlier batches made me sick was that the beans did not ferment thoroughly. The beans were hard enough that the natto bacteria had a difficult time fermenting the inside of the beans. The softness of the well cooked beans facilitated a more thorough fermentation that diminished the starches that caused my digestion issues. I hope this helps anyone experiencing similar issues.

Thanks for reporting back!