Nearly complete review of what we know about kefir:
Historically, kefir has been recommended for the treatment of several clinical conditions such as gastrointestinal problems, hypertension, allergies, and ischemic heart disease (Farnworth and Mainville, 2008; Rattray and O’Connel, 2011). However, the variability inherent in kefir production conditions in different assays makes it difficult to conduct comparisons between reported scientific results (Farnworth, 2005; Farnworth and Mainville, 2008; Rattray and O’Connel, 2011).The above review didn't address the nutritional content of kefir besides B-12. It's rumored to be high in calcium, magnesium and K-2, but as noted above, the variability in production methods makes it hard to guess at the actual nutritional content of a particular culture.
I've had this craving for kefir again a few times since, and a friend provided me with some grains and talked me into attempting it myself. The results are mixed. My cultured milk was drinkable, but quite tart and needed significant sugar and fruit boost. It also takes dedication to keep the culture going, you can't just not buy milk and stop feeding it this week, if you refrigerate or freeze the culture to prolong time between feedings, you have to plan around warming it and reviving it before you can start a fresh batch. So I've pretty much given up on culturing it myself.
Every now and then I get a craving, and I go ahead and buy some. I usually get Lifeway Organic Whole Milk Kefir, Wildberries and Cream flavor. I'm not normally a fan of organic, but this product is whole milk, from cows on pasture (organic cows must have some pasture, although they might not be entirely grass fed) and it tastes great.
This is not a ketogenic food, but approaches the "40/30/30 balance" that some folks on moderate carb diets aspire to: