I use stevia almost everyday in kefir, not even a 1/8 teaspoon. I personally am satisfied with the large amount of reading I have done on it... plus it has been used traditionally for a great number of years. I have seen the study re: reproductive problems, but I think they were eating their weight in stevia. I think any substance would do damage at that rate.
Now, FOS however, that is in Stevia Plus, I'm not so sure about. I've seen several warnings on it lately (more in link below)
Let me tell you, I have spent hundreds of dollars on powdered probiotics in the past couple years... and they helped for sure. But homemade kefir kicks their butt.
You get trillions
of live probiotics in just a small amount of kefir, compared to just billions in dried form in the capsules which may or not be totally active. Plus the probiotics in your own kefir are freshly born and in their natural growth medium, so they are thought to colonize the gut more effectively.
Yogurt and kefir more effective than probiotic pills (also see FOS warning):
I love the Body Ecology powder kefir starter:
It's very easy to culture, you add warm milk and let sit on counter for 18 to 24 hrs. It reproduces exactly the same taste every time. You can make a lot from just one packet if you divide it the right way. (There are 6 packets in a box.)
One packet makes 1 qt. of kefir, which then you can use a little finished kefir as a starter make up to a gallon at a time. You can divide it up to 7 times. However, I figured out if you take the first quart and make multiple batches, then those batches can go 7 times, etc. etc. I have been putting some in the frig. to culture very slowly (cold slows growth) and some on the counter to culture first.
I have some awesome live grains now though. They took a couple of days to recover from their journey and now they are reproducing like mad. The grains can last forever with proper care. They also culture in about 24 hrs at room temperature but they do take a little more work. Just a little though... I usually buzz my finished kefir with a stick blender to make it creamy and then let it mature for another few hours to a day to get nice and tart. Some people think the grains are yucky... they are like little beads of tapioca stuck together, I used to think that too but now they are my friends :LOL
I'm eating the grains too, which is another huge benefit...a neverending supply of probiotic pills! So I'll save the powder starter for vacation or in an emergency.
Let me know if you have any questions but I'm seriously worshipping kefir right now, it's amazing. I've spent a long time trying to heal our guts for good and I think this is indeed the answer.