Is galactose a carbohydrate to worry about ? If it does not stimulate insulin production then it would probably not weaken the aims of a low carb diet (appetite reduction, weight loss, etc. etc).

I eat/drink kefir every day and its sourness (compared with commercail natural yogurt) encourages me to believe that its quite low carb and high in lactic acid. It also gets more sour as time goes on, though it seldom lasts long enough, to make me believe that it really is "live".

Commercial yogurt by contrast is bland and unchanging.