I'm not convinced that kefir should be regarded as low carb. The thing is that the body pretty effortlessly converts its own lactate to glucose when oxygen is abundant, so why wouldn't it do so to the lactic acid in the kefir? Even so, any whole milk product isn't going to have a terribly high glycemic index because the milk-fat slows down absorption so much.

And if you want to reduce the carbs even further then do what I do. Make kefir out of a 50/50 mix of milk and cream. Don't use ultrapasturized if you can avoid it. You can mix kefir with most anything for flavor. Strawberries work great.

But I drink most of it straight. I put it in the blender to smooth it out. Sometimes I add raw eggs.